-
Notifications
You must be signed in to change notification settings - Fork 0
/
2DTranslationInvariantSPT.tex
2423 lines (2417 loc) · 231 KB
/
2DTranslationInvariantSPT.tex
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
\documentclass[11pt,a4paper,twoside]{article}
\input{myPackage.tex}
%For ArXiv version use 0 for CIMP version use 1
\def\version{0}
\newcommand{\versionDifference}[2]{\ifthenelse{\version=0}{#1}{#2}}
\title{SPT indices emerging from translation invariance in two-dimensional quantum spin systems}
\author{Tijl Jappens\footnote{Institute for Theoretical Physics, Katholieke Universiteit Leuven.}}
\date{\today}
\numberwithin{equation}{section}
\begin{document}
\maketitle
\begin{abstract}
We consider SPT-phases with on-site $G$ (where $G$ is any finite group) symmetry for two-dimensional quantum spin systems. We then impose translation invariance in one direction and observe that on top of the $H^3(G,\TT)$-valued index constructed in \cite{ogata2021h3gmathbb}, an additional $H^2(G,\TT)$-valued index emerges. We also show that if we impose translation invariance in two directions, on top of the expected $H^3(G,\TT)\oplus H^2(G,\TT)\oplus H^2(G,\TT)$ valued index, an additional $H^1(G,\TT)$-valued index emerges.
\end{abstract}
\section{Introduction}
In 2010, Chen, Gu and Wen \cite{chen_gu_wen_2011} introduced the notion of symmetry-protected topological phases of matter (SPT). They first considered one-dimensional matrix product states and later on, Chen, Liu and Wen \cite{Chen_2011}, extended this to two-dimensional projective entangled pair models. Afterwards, in \cite{Chen_2013} this concept was extended to other dimensions. This last reference used a setup involving so-called lattice non-linear sigma models and provided an $H^{d+1}(G,U(1))$ valued index for any $d$-dimensional lattice non-linear sigma model. The standard setup for defining SPT phases is in quantum spin systems (defined in section \ref{sec:QuasiLocalC*Algebra}). To define SPT phases in this setting, one needs to fix a finite group $G$ with an on-site group action $g\mapsto U_g$ (with $g\in G$), defining a global group action $\beta_g$ (also defined in section \ref{sec:QuasiLocalC*Algebra}). A state $\omega$, is then called $G$-invariant, if $\omega\circ\beta_g=\omega$. Afterwards, one needs to restrict the space of states. We\footnote{There are other definitions possible like for instance the concept of invertible G-invariant states used in \cite{kapustin2021classification} or the unique gapped ground state of a G invariant interaction presented in the introduction of \cite{ogata2021h3gmathbb}.} ask that our states are short-range entangled (SRE), see definition \ref{def:sre}. A state $\omega$ is short-range entangled if there is a disentangler $\gamma$. This is a locally generated automorphism, produced by a one-parameter family of interactions $\Phi\in\BB_{F_\phi}([0,1])$ ($\gamma=\gamma_{0;1}^\Phi$ as defined in section \ref{sec:Interactions}) satisfying that $\omega\circ\gamma$ is a product state. Combining these two definitions, we say that $\omega$ is an SPT state if it is short-range entangled and $G$-invariant.
\\\\
One then defines an equivalence relation on these SPT states by saying that $\omega_1$ is equivalent to $\omega_2$ with respect to the on-site group action $U$ if there exists a $G$-invariant one-parameter family of interactions $\Phi\in\BB_{F_\phi}([0,1])$ such that $\omega_1\circ\gamma^\Phi_{0;1}=\omega_2$ (again, see section \ref{sec:Interactions} for the definitions). One can then extend this equivalence to the stronger notion of being stably equivalent. This goes as follows: one defines an operation called stacking that takes two SPT states $\omega_1$ and $\omega_2$ and outputs a third one $\omega_1\otimes_{\text{stack}}\omega_2$ (and similarly for the group action). This $\otimes_\text{stack}$ is defined in section \ref{sec:QuasiLocalC*Algebra}. In short, it is the tensor product at the level of the on-site Hilbert space. One then defines another equivalence relation and says that two SPT states with on-site group actions $(\omega_1,U_1)$ and $(\omega_2,U_2)$ are stably equivalent if and only if there exist trivial\footnote{A trivial state is a $G$-invariant product state that transforms trivially under the on-site group action (see remark \ref{rem:NontrivialProductState}).} SPTs with their group actions, $(\phi_1,\tilde{U}_1)$ and $(\phi_2,\tilde{U}_2)$ and a ($G$ independent) unitary $V$ mapping between the respective on-site Hilbert spaces\footnote{The reader can think of this $V$ as being a unitary transformation of the on-site group action.}, such that
\begin{enumerate}
\item $V^\dagger U_{1,g}\otimes \tilde{U}_{1,g}V=U_{2,g}\otimes \tilde{U}_{2,g}$ for all $g\in G$.
\item $\omega_1\otimes_{\text{stack}}\phi_1\circ i_V$ (where $i_V$ is defined in section \ref{sec:QuasiLocalC*Algebra}) is equivalent to $\omega_2\otimes_{\text{stack}}\phi_2$ with respect to the above on-site group action.
\end{enumerate}
In one spatial dimension so-called matrix product states (\cite{Chen_2011},\cite{pollman2012symmetry},\cite{schuch2011MatrixProduct}) can be used to construct non-trivial SPT states. Later on and more generally it was shown in \cite{ogata2019classification} that any $G$-invariant state satisfying the split property (this includes any SRE state) carries an $H^2(G,\TT)$-valued\footnote{By $H^n(G,\TT)$ we mean the n-th (Borel) group cohomology of $G$ with coefficients in the torus $\TT$ (seen as a (group) module under addition with trivial group action).} index and that this index is constant on the (stable) equivalence classes. Later on in \cite{kapustin2021classification} it was then shown that this classification problem is complete (the index, seen as a map from the set of stable equivalence classes to $H^2(G,\TT)$ is injective.). In two spatial dimensions, more recently in \cite{ogata2021h3gmathbb}, it was proven there is an $H^3(G,\TT)$-valued index that is constant on the (stable) equivalence classes\footnote{In \cite{ogata2021h3gmathbb}, there is no mention of the stacking operation but using remark \ref{rem:StackingH3ValuedIndex} and remark \ref{rem:OnSiteUnitaryTransformationH3ValuedIndex}, one can extend it to the stable equivalence class.}. In this paper, we will denote this $H^3(G,\TT)$-valued index of a state $\omega$ by $\textrm{Index}_{\text{2D}}(\omega)$.
\\\\
We've used stacking to define the stable equivalence relation. Stacking however plays a more general role. It is widely believed that it allows us to define an (abelian) group structure on the set of stable equivalence classes\footnote{The stacking with a trivial state will then be related to the identity of this group}. Although it is nowhere stated explicitly, the author thinks that the literature (like, for example, \cite{kapustin2021classification}) suggests the following conjecture:
\begin{conjecture}\label{conj:StableEquivGroupStructure}
Take some fixed group and a fixed lattice. Let $S$ be the set of stable SPT classes defined through the above equivalence class. Let $*$ be the map
\begin{equation}
*:S^2\rightarrow S:(\expval{\omega_1,U_1}_{\sim},\expval{\omega_2,U_2}_{\sim})\mapsto \expval{\omega_1\otimes_\text{stack}\omega_2,U_1\otimes U_2}_{\sim}.
\end{equation}
Then $*$ is well-defined (independent of the choice of representative) and $S$ equipped with the $*$ operation forms an abelian group.
\end{conjecture}
Before proceeding, we make three remarks on this conjecture:
\begin{enumerate}
\item The claim that $*$ is well-defined and abelian is trivial. Namely, by letting $i_V$ be the automorphism that exchanges the two algebras that are being stacked, one can exchange the order of the stacking freely. By using
\begin{equation}
\omega_1\circ\gamma^{\Phi_1}_{0;1}\otimes_\text{stack}\omega_2\circ\gamma^{\Phi_2}_{0;1}=(\omega_1\otimes_{\text{stack}}\omega_2)\circ\gamma^{\Phi_1\otimes\id+\id\otimes\Phi_2}_{0;1}\sim\omega_1\otimes_{\text{stack}}\omega_2,
\end{equation}
one can show that this is a well-defined map.
\item A representative of the inverse is sometimes called a $G$-inverse.
\item From a category point of view, if one assumes that this conjecture is true (for some subclass of groups that is a category), it is not hard to see that it gives rise to a contravariant functor from this category of groups to the category of abelian groups (say $S[G]$). More specifically, to each group morphism $f:G_1\rightarrow G_2$, one can find a group morphism $\tilde{f}:S[G_2]\rightarrow S[G_1]:\expval{\omega,U}_\sim\mapsto \expval{\omega,U\circ f}_\sim$ and this $\tilde{f}$ is indeed invariant on the choice of representative (if two states can be connected while preserving the symmetry action $\beta$, they can certainly be connected while preserving the symmetry $\beta\circ f$).
\end{enumerate}
In what follows, we will call $S$ with the above group structure the stable SPT classification. In this paper, we consider the 2D case with the (stable) equivalence relation as presented here but with one notable difference. We will only consider states, interactions, and on-site symmetries that have a translation symmetry in one direction. There is a conjecture about the SPT classification of such states, see section 3.1.5.1 of \cite{xiong2019classification} for a more general and detailed exposition (which was partially based on \cite{Chen_2013}).
\begin{conjecture}\label{conj}
The set of translation invariant SPTs under stable equivalence\footnote{In the stable equivalence relation for translation invariant states we ask that the on-site symmetry is translation invariant and that any path connecting two states and each trivial state is not only G-invariant but also translation invariant.} also satisfies conjecture \ref{conj:StableEquivGroupStructure}. Let $g$ be the inclusion map from the space of 2d translation invariant SPT states to the more general set of 2d SPT states. Let $f$ be the map that takes a 1d SPT state and outputs a translation invariant 2d SPT state by taking the tensor product in the direction of the translation symmetry. The sequence
\begin{equation}
0\rightarrow\{\text{1d SPT states}\}\stackrel{f}{\rightarrow}\{\text{2d translation invariant SPT states}\}\stackrel{g}{\rightarrow}\{\text{2d SPT states}\}\rightarrow 0
\end{equation}
induces a sequence (of group morphisms) on the stable equivalence classes. By this, we mean that the class of $f(\phi)$ only depends on the class of $\phi$ and similarly for $g$. Moreover, this induced sequence is exact and split.
\end{conjecture}
This implies that
\begin{equation}
\{\text{2d translation invariant SPT classification}\}\simeq \{\text{1d SPT classification}\}\oplus \{\text{2d SPT classification}\}.
\end{equation}
Since a 1d SPT state carries an $H^2(G,\TT)$ valued index and a 2d SPT state carries an $H^3(G,\TT)$ valued index, this means that 2d SPT states with a translation symmetry should carry an $H^2(G,\TT)\oplus H^3(G,\TT)$ valued index. This is consistent with the result of section XII of \cite{Chen_2013}.
\\\\
The first result of this paper is the construction of an $H^2(G,\TT)$ valued index (which we will denote by $\textrm{Index}$) on the space of translation invariant SPT states that is consistent with conjectures \ref{conj:StableEquivGroupStructure} and \ref{conj}. By being consistent with the conjecture it is meant (among other things) that, if $\textrm{Index}_1$ is the one-dimensional SPT index from \cite{ogata2019classification}, then $\textrm{Index}(f(\omega))=\textrm{Index}_1(\omega)$ for any 1d SPT $\omega$. This construction highly relies on the objects that are present in the construction of the 2d SPT index in \cite{ogata2021h3gmathbb}.
\\\\
We also look at the case where there is a second translation symmetry (so the system is translation invariant in both $x$ and $y$ directions). For such systems, there is the following conjecture (see again \cite{xiong2019classification} and \cite{Chen_2013}):
\begin{conjecture}\label{conj2}
The space of SPTs, translation invariant in two directions under stable equivalence also satisfies conjecture \ref{conj:StableEquivGroupStructure}. Let $g$ be the inclusion map from the space of 2d SPT states that are translation invariant in both $x$ and $y$ directions to the more general set of 2d SPT states with translation invariance in the $x$ direction only. Let $f$ be the map that takes a 1d translation invariant SPT state and outputs a 2d SPT state that is translation invariant in both $x$ and $y$ directions by taking the tensor product in the $y$ direction. The sequence
\begin{equation}
0\rightarrow\left\{\begin{matrix}\text{1d translation invariant}\\ \text{SPT states}\end{matrix}\right\}\stackrel{f}{\rightarrow}\left\{\begin{matrix}\text{2d SPT states with two}\\ \text{translation symmetries}\end{matrix}\right\}\stackrel{g}{\rightarrow}\left\{\begin{matrix}\text{2d SPT states translation}\\ \text{invariant in $x$ direction}\end{matrix}\right\}\rightarrow 0
\end{equation}
induces a sequence (of group morphisms) on the stable equivalence classes. By this, we mean that the class of $f(\phi)$ only depends on the class of $\phi$ and similarly for $g$. Moreover, this induced sequence is exact and split.
\end{conjecture}
Translation invariant SPT states in one spatial dimension are known to carry an $H^2(G,\TT)\oplus H^1(G,\TT)$ valued index (see section \ref{sec:OneDimensionalIndices} for a construction of these indices consistent with the rest of the setup). From this and the last two conjectures, we expect there to be an
\begin{equation}\label{eq:2TranslationsIntroduction}
H^3(G,\TT)\oplus H^2(G,\TT)\oplus H^2(G,\TT)\oplus H^1(G,\TT)
\end{equation}
valued index. The first part of the index is just the above mentioned $\textrm{Index}_{2d}$. The following two parts can be related to the case of a single translation symmetry as follows. Let $\mu$ be the automorphism that rotates the lattice by 90° and let $\textrm{Index}(\omega)$ be the index as constructed before (this is the second part of \ref{eq:2TranslationsIntroduction}). The third part of the index is now given by $\textrm{Index}(\omega\circ\mu)$ (the state rotated by 90°). The last part of the index requires a different construction altogether. It can be thought of as being the charge in the Brillouin zone.
\\\\
A final remark:
\begin{remark}
As noticed in \cite{Chen_2013}. The groups in which these indices take values can be concisely written out. Using that
\begin{align}
H^0(\ZZ,\TT)&\cong \TT& H^1(\ZZ,\TT)&\cong \TT& H^2(\ZZ,\TT)&\cong 0&H^3(\ZZ,\TT)&\cong 0
\end{align}
and inserting this into the K\"unneth formula for $\ZZ\times G$ gives
\begin{align}
H^2(\ZZ \times G,\TT)&\cong \bigoplus_{i=0}^2 H^i(\ZZ,\TT)\otimes H^{2-i}(G,\TT)\cong H^2(G,\TT)\oplus H^1(G,\TT)\\
H^3(\ZZ \times G,\TT)&\cong \bigoplus_{i=0}^3 H^i(\ZZ,\TT)\otimes H^{3-i}(G,\TT)\cong H^3(G,\TT)\oplus H^2(G,\TT).
\end{align}
This result can in turn be used to work out the K\"unneth formula for $\ZZ^2\times G$
\begin{equation}
H^3(\ZZ^2\times G,\TT)\cong \bigoplus_{i=0}^3 H^i(\ZZ,\TT)\otimes H^{3-i}(\ZZ\times G,\TT)\cong H^3(G,\TT)\oplus H^2(G,\TT)\oplus H^2(G,\TT)\oplus H^1(G,\TT).
\end{equation}
\end{remark}
The layout of this paper is as follows: First in section \ref{sec:Setup} we explain the setup, define the concept of locally generated automorphisms, and give the algebraic definition of group cohomology. In section \ref{sec:Results_1} we state the two results for SRE states. In section \ref{sec:Results_2}, we state the first result using the weaker assumption \ref{assumption} and the second result using the weaker assumption \ref{assumption:2Translations}. It is using these weaker assumptions that we then prove the statements. The rest of the paper provides a proof of these statements. The results in this paper rely heavily on the methods that were developed in \cite{ogata2021h3gmathbb}.
\subsection*{Acknowledgements}
T.J. was supported in part by the FWO under grant G098919N.\\\\
We are grateful to the referees of Communications in Mathematical Physics for their constructive input during the review process. For example, we are very grateful for the proposed changes of lemma \ref{lem:SplittingOfUnitary}, the mistake they found in section \ref{sec:examples} (the previous assumption was too weak), and the mistakes they found in section \ref{sec:AllIndicesInvariantUnderLGA}.
\subsection*{Data availability statement}
No new data were created or analyzed in this study. Data sharing is not applicable to this article.
\versionDifference{\subsection*{ArXiv version}This manuscript is a (more extensive) ArXiv version of a paper that will be published in communications in mathematical physics. To access the journal version of the paper, see \url{https://rdcu.be/dwtjE}.}{\subsection*{ArXiv version}This paper is a more compact version of the ArXiv version \cite{jappens2023spt}. We will sometimes refer to this version.}
\section{Setup and definitions}\label{sec:Setup}
In this paper, we work in the two-dimensional lattice $\ZZ^2$. We will first need some specific subsets of $\ZZ^2$, so let
\begin{align}
L&\defeq \left\{(x,y)\in\ZZ^2\left|x<0\right.\right\},&R&\defeq \left\{(x,y)\in\ZZ^2\left|x\geq 0\right.\right\}\\
U&\defeq \left\{(x,y)\in\ZZ^2\left|y\geq 0\right.\right\},&D&\defeq \left\{(x,y)\in\ZZ^2\left|y<0\right.\right\}
\end{align}
be the left, right, upper, and lower half-planes respectively, and let
\begin{equation}
C_\theta\defeq \left\{(x,y)\in\ZZ^2\left|\tan(\theta)\leq\abs{\frac{y}{x}}\right.\right\}
\end{equation}
be the horizontal cone (the green area in figure \ref{fig:SetupWithQAutomorphism}). We will use $\tau$ to denote the bijection that moves every element of $\ZZ^2$ one site upward. Similarly, we let $\nu$ denote the bijection that translates every element of $\ZZ^2$ by one site to the right. In what follows we will sometimes need to widen our cone or other subsets of $\ZZ^2$ vertically by one site. For this purpose we define $W$ such that for any $\Gamma\subset\ZZ^2$,
\begin{equation}
W(\Gamma)\defeq \Gamma\cup\tau(\Gamma)\cup\tau^{-1}(\Gamma).
\end{equation}
For example, the red area in figure \ref{fig:SetupWithQAutomorphism} is $W(C_\theta)^c$. In the later part, we will also need to rotate our lattice by $90^\circ$ (clockwise) so call $\mu$ the bijection on $\ZZ^2$ that does precisely this.\footnote{We will not discuss rotation invariant states in this paper. The $\mu$ is only defined to make certain constructions work.} Finally, we will need to define the horizontal lines and the finite horizontal line
\begin{align}
L_j&\defeq \{(i,j)|i\in\ZZ\}&L_j^n&\defeq \{(i,j)|i\in\ZZ\cap[-n,n]\}.
\end{align}
\subsection{Quasi local \texorpdfstring{$C^*$}{}-algebra}\label{sec:QuasiLocalC*Algebra}
The setup in this paper will be very similar to the setup in \cite{ogata2021h3gmathbb} and is just the standard setup for defining quantum spin systems. For the rest of this paper, take $d\in\NN_+$ arbitrary. This number will be called the on-site dimension\footnote{In principle in the case where there is only one translation we can let $d$ be $x$-dependent but for simplicity let us take $d$ constant over the lattice.}. For each $z\in\ZZ^2$, let $\AA_{\{z\}}$ be an isomorphic copy of $\BB(\CC^d)$ (the bounded operators on $\CC^d$). In what follows, let $\mathfrak{G}_{\ZZ^2}$ be the set of finite subsets of $\ZZ^2$. For any $\Lambda\in\mathfrak{G}_{\ZZ^2}$, we set $\AA_\Lambda=\bigotimes_{z\in\Lambda}\AA_{\{z\}}$. We define the local algebra as $\AA_{\text{loc}}=\bigcup_{\Lambda\in \mathfrak{G}_{\ZZ^2}}\AA_{\Lambda}$ and define the quasi local $C^*$ algebra as the norm closure of the local algebra ($\AA=\overline{\AA_{\text{loc}}}$). Similarly, for any (possibly infinite) subset $\Gamma\subset\ZZ^2$ we set $\AA_{\text{loc},\Gamma}=\bigcup_{\Lambda\in \mathfrak{G}_{\Gamma}}\AA_{\Lambda}$ and $\AA_\Gamma=\overline{\AA_{\text{loc},\Gamma}}$.\\\\
Throughout this paper, we will sometimes require a stronger form of locality than merely being in the norm completion of the local algebra. Specifically when $\Gamma=L_j$ is a horizontal line. We will say that an operator $A\in\AA_{L_j}$ is summable if and only if there exists a sequence $A_n\in\AA_{L_{j}^n}$ on the finite horizontal lines such that
\begin{equation}
\sum_{i=0}^{\infty}\norm{A-A_n}<\infty.
\end{equation}
We will need to define some automorphisms on this algebra using the bijections defined previously. To this end, define the isomorphisms
\begin{align}
\tau&:\AA_\Gamma\rightarrow\AA_{\tau(\Gamma)}&\nu&:\AA_\Gamma\rightarrow\AA_{\nu(\Gamma)}&\mu&:\AA_\Gamma\rightarrow\AA_{\mu(\Gamma)}
\end{align}
as the translation upwards, the translation to the right, and the right-handed rotation respectively. By construction, these isomorphisms are automorphisms if $\Gamma$ is taken to be $\ZZ^2$ (because $d$ is a constant throughout the lattice). Clearly if $\Gamma=\ZZ$ (by which we mean again the $x$-axis $(\ZZ,0)$) only one of these translation automorphisms descends to an automorphism on $\AA_{\ZZ}$. This automorphism is then also simply denoted as $\nu$.\\\\
We will need to define one additional class of automorphisms. For any set of unitaries $V_i\in\UU(\CC^d)$ (labelled by $i\in\ZZ^2$), we define the (unique) automorphism $i_V^\Gamma\in\Aut{\AA_\Gamma}$ (for all $\Gamma\subset \ZZ^2$) such that $i_V^\Gamma (A)=\Ad{\otimes_{i\in I} V_i}(A)$ for all $I\subset\Gamma$ finite and $A\in\AA_I$. This class of automorphisms will be used to define a group action on the algebra. More specifically, let $G$ be a finite group and let $U_i\in\hom(G,\UU(\AA_i))$ (for $i\in\ZZ^2$) be the on-site group action. Let $\beta^\Gamma\in\hom(G,\Aut{\AA_\Gamma})$ (for any $\Gamma\subset\ZZ^2$) be such that
\begin{equation}
\beta^\Gamma_g(A)=i_{U(g)}^\Gamma=\Ad{\otimes_{i\in I} U_i(g)}(A)
\end{equation}
for any $g\in G$, $I\subset\Gamma$ finite and $A\in\AA_I$. Clearly, any unitary transformation of our representation $U(\cdot)\rightarrow V^\dagger U(\cdot) V$ induces a transformation of the group action $\beta_g\rightarrow i_{V}^{-1}\circ\beta_g\circ i_V$.\\\\
Throughout our paper when we are discussing translation invariance in the vertical direction we will ask that the group action is translation invariant in the vertical direction ($\tau\circ\beta_g^\Gamma=\beta_g^{\tau(\Gamma)}\circ\tau$). If we also have translation invariance in the horizontal direction, we will also ask that the group action be translation invariant in that direction as well ($\nu\circ\beta_g^\Gamma=\beta_g^{\nu(\Gamma)}\circ\nu$). As it turns out, in showing that the $H^1$-valued index is consistent with all the conjectures of the introduction, we will even require that the on-site group action $U_i(g)$ is the same at each site. In what follows we will always assume this. This means that when we denote an on-site symmetry action we merely have to give one representation $U\in\hom(G,\UU(\CC^d))$, and when we denote a unitary transformation of the on-site Hilbert space we only have to give a single unitary $V\in \UU(\CC^d)$, we will use this notation frequently.\\\\
By construction, there is a tensor product operation on this $C^*$ algebra in the sense that for any $\Gamma_1,\Gamma_2\subset\ZZ^2$ satisfying that $\Gamma_1\cap\Gamma_2=\emptyset$ we can define a bilinear, surjective map
\begin{equation}
\otimes:\AA_{\Gamma_1}\times\AA_{\Gamma_2}\rightarrow \AA_{\Gamma_1\cup\Gamma_2}.
\end{equation}
There is however a second tensor product operation on this $C^*$ algebra that we will use. We will call it the stacking operation. It is such that for any $\Gamma\subset\ZZ^2$ we define the bilinear, surjective map
\begin{equation}
\otimes_{\text{stack}}:\AA_{\Gamma}\times\AA_{\Gamma}\rightarrow \AA^2_{\Gamma}
\end{equation}
where $\AA^2$ is the quasi-local $C^*$ algebra on $\ZZ^2$ constructed from an on-site algebra $\BB(\CC^d)\otimes\BB(\CC^d)\simeq \BB(\CC^{d\times d})$\footnote{This can also be used to stack two $C^*$-algebras with different on-site Hilbert spaces, this was used in the introduction. In the rest of the paper we will for simplicity of notation (but without loss of generality) only stack two identical $C^*$-algebras on top of each other.}. We will also need to define the stacking of the group action by which we mean
\begin{equation}
(\beta_g\otimes_{\text{stack}}\beta_g)^\Lambda=\bigotimes_{z\in\Lambda}\Ad{U(g)\otimes U(g)_z}
\end{equation}
for any $\Lambda\in\mathfrak{G}_{\ZZ^2}$ (in fact stacking can be defined for any automorphism, not just the group action).
\subsection{States on \texorpdfstring{$\AA$}{}}\label{sec:States}
We will use $\PP(\AA)$ to denote the set of pure states on $\AA$ (see \cite{bratteli1979operator}). In this paper, we will often refer to the GNS triple. For its definition, construction, and properties we refer to \cite{bratteli1979operator}. We will sometimes write the tensor product of states $\omega\otimes\phi$ to be such that $(\omega\otimes\phi)(a\otimes b)=\omega(a)\phi(b)$ and similarly for the stacking tensor product. We will call a pure state $\phi$ on $\AA_\Gamma$ a product state if for any $\Lambda\subset\Gamma$, the restriction $\phi|_{\AA_\Lambda}$ is still pure. We will call a state $\omega$, $G$-invariant if $\omega\circ\beta_g=\omega$ (where $\beta_g=i_{U(g)}$ with $U$ an on site group action). Moreover, we say that a $G$-invariant product state $\phi$ is trivial with respect to $U$ (we will sometimes denote this as $(\phi,U)$ is trivial) if $\phi(U_i(g))=1$ for all $i\in\ZZ^2$.\\\\
There is a natural way to construct a pure $G$-invariant state on the quasi local $C^*$-algebra over $\ZZ^2$, $\AA_{\ZZ^2}$ using a pure $G$-invariant state on the quasi local $C^*$-algebra over $\ZZ$, $\AA_{L_0}$\footnote{When applied to a trivial state on $\AA_{L_0}$ this will also give a trivial state on $\AA_{\ZZ^2}$.}.
\begin{definition}\label{def:InfiniteTensorProduct}
Let $\phi\in\PP(\AA_{L_0})$ be a state that is $G$-invariant under a group action $\beta_g^{L_0}$. Define $\phi_i\in\PP(\AA_{L_i})$ as $\phi_i:=\phi_0\circ\tau^{-i}$. We define the infinite tensor product state $\omega_\phi$ as $\omega_\phi:=\bigotimes_{j\in\ZZ}\phi_j$. This is a $G$-invariant pure state over $\ZZ^2$ that is invariant under the automorphism $\tau$.
\end{definition}
The proof that this is a well-defined state is done in definition \ref{def:InfiniteTensorProductState}.
\subsection{Interactions and locally generated automorphisms}\label{sec:Interactions}
An interaction $\Phi$ is a map
\begin{equation}
\Phi: \mathfrak{G}_{\ZZ^2}\rightarrow \AA_{\text{loc}}: I \mapsto \Phi(I)
\end{equation}
where $\Phi(I)\in\AA_I$ is hermitian ($\Phi(I)=\Phi(I)^*$). We will sometimes use the restriction of an interaction, $\Phi_\Gamma$ for $\Gamma\subset\ZZ^2$. This means setting all $\Phi(I)=0$ when $I$ is not in $\Gamma$. Following the work done in \cite{doi:10.1063/1.5095769}, will use $\norm{\Phi}_F$ to indicate the $F$-norm of $\Phi$ where $F$ is an $F$-function. We will use $\BB_{F}([0,1])$ to denote the one-parameter families of interactions with norm continuous therms and uniformly bounded $F$-norms. Just as was done in \cite{doi:10.1063/1.5095769}, for any $\Phi\in \BB_{F}([0,1])$, we use $\gamma^{\Phi}_{s;t}$ to denote the locally generated automorphism (LGA) generated by $\Phi$ from $s$ to $t$. Following \cite{ogata2021h3gmathbb}, we will fix a specific family of monotonically decreasing positive functions by saying that for any $0<\phi<1$ we define
\begin{equation}\label{eq:OurFFunction}
F_\phi:\RR^+\rightarrow\RR^+:r\mapsto \frac{\exp(-r^\phi)}{(1+r)^4}.
\end{equation}
This $F$-function is particularly useful to us because, as was shown in \cite{ogata2021h3gmathbb}, if $\Phi\in\BB_{F_\phi}([0,1])$, we can decompose the automorphism into different parts. More precisely, we can show that $\gamma^{\Phi}_{s;t}\in\QAut{\AA}$ where $\QAut{\AA}$ is defined in \ref{def:QAut}\footnote{In appendix \versionDifference{\ref{sec:properties-of-locally-generated-automorphisms-1d}}{B of \cite{jappens2023spt}} we show a stronger version of this statement.}.
\\\\
Sometimes we will say that an interaction is $G$-invariant. By this we simply mean that $\beta_g(\Phi(I))=\Phi(I)$ (for all $I\in\mathfrak{G}_{\ZZ^2}$). Similarly, if we say an interaction is translation invariant we mean that $\tau(\Phi(I))=\Phi(\tau(I))$ (for all $I\in\mathfrak{G}_{\ZZ^2}$). It should be clear that if an interaction is $G$-invariant (translation invariant), then the LGA it generates commutes with the group action (the translation automorphism) as well.
\subsection{The stable equivalence class}\label{sec:StableEquivalenceClasses}
We will now define a subset of these states that we will call short-range entangled (SRE):
\begin{definition}\label{def:sre}
Let $\omega\in\PP(\AA)$. We say that $\omega$ is an SRE state if and only if there exists a $\phi\in]0,1[$ such that there exists an interaction $\Phi\in\BB_{F_\phi}([0,1])$ such that $\omega\circ\gamma^\Phi_{0;1}$ is a product state. We then call $\gamma^\Phi_{0;1}$ a disentangler for $\omega$.
\end{definition}
On the set of $G$-invariant SRE states we will now define three stable equivalence classes depending on the additional imposed symmetry:
\begin{definition}
Take $(\omega_1,U_1)$ and $(\omega_2,U_2)$ elements of
\begin{equation}
S_0=\{(\omega,U)\in\PP(\AA)\times\hom(G,U(\CC^d))|\omega\text{ is SRE},\:\omega\circ i_{U(g)}=\omega\:\forall g\in G\}
\end{equation}
for two algebras $\AA_1$ and $\AA_2$\footnote{With two different algebras we simply mean two different on-site dimensions because we already fixed each on-site dimension to be identical.}. We say that $\expval{\omega_1,U_1}_\sim=\expval{\omega_2,U_2}_\sim$ if and only if there exists a $\phi\in]0,1[$ such that there exists a $G$-invariant interaction $\Phi\in\BB_{F_\phi}([0,1])$, trivial elements of $S_0$ (see subsection \ref{sec:States}), $(\phi_1,\tilde U_1)$ and $(\phi_2,\tilde U_2)$ for algebras $\tilde\AA_1$ and $\tilde\AA_2$ respectively and an on-site unitary such that
\begin{align}
\omega_1\otimes_{\text{stack}}\phi_1\circ i_V&=\omega_2\otimes_{\text{stack}}\phi_2\circ\gamma^\Phi_{0;1}&V^\dagger U_{1}(g)\otimes \tilde{U}_{1}(g)V&=U_{2}(g)\otimes \tilde{U}_{2}(g).
\end{align}
\end{definition}
We also define similar equivalence classes $\expval{\cdot}_\sim^1,\expval{\cdot}_\sim^2$ and $\expval{\cdot}_\sim^3$ on
\begin{align}
\nonumber
S_1&=\{(\omega,U)\in\PP(\AA)\times\hom(G,U(\CC^d))|\omega\text{ is SRE},\:\omega\circ i_{U(g)}=\omega\:\forall g\in G,\:\omega\circ\tau=\omega\}\\
S_2&=\{(\omega,U)\in\PP(\AA)\times\hom(G,U(\CC^d))|\omega\text{ is SRE},\:\omega\circ i_{U(g)}=\omega\:\forall g\in G,\:\omega\circ\nu=\omega\}\\
\nonumber
S_3&=\{(\omega,U)\in\PP(\AA)\times\hom(G,U(\CC^d))|\omega\text{ is SRE},\:\omega\circ i_{U(g)}=\omega\:\forall g\in G,\:\omega\circ\tau=\omega,\:\omega\circ\nu=\omega\}
\end{align}
respectively. Here we now also demand that the interactions and the trivial states are invariant under the additional translation symmetries.
\section{Results}
To formulate the results, we will often use $H^n(G,\TT)$ to denote the n-th (Borel) group cohomology of $G$ with coefficients in the torus $\TT$ (seen as a (group) module under addition with trivial group action). For the definition of these group cohomology modules, we refer to \cite{benson1991representations}.
\\\\
This section will contain three different parts. First, we discuss the main result starting from some rather abstract assumptions. In the second part, we present the claim that these assumptions are implied by some more natural assumptions relating to short-range entanglement. In the last part of the section we compare our assumptions to those made in \cite{ogata2021h3gmathbb}.
\subsection{Statement of the result in terms of Q-automorphisms}\label{sec:Results_2}
\begin{figure}
\centering
\def\s{0.5}
\resizebox{0.27\textwidth}{!}{%
\input{Figures/AlphaLeftRight.tex}}
$\qquad$
\def\s{0.4}
\resizebox{0.32\textwidth}{!}{%
\input{Figures/Cone_W_Nu_Eta.tex}}
\caption{These figures indicate the support area of the different automorphisms in a particular decomposition of the $\textrm{QAut}$. The angle $\theta$ needs to be smaller than or equal to what was indicated here so that the $\Theta$ and the $\eta_g$ (possibly after widening by one site vertically and one site horizontally) commute.}
\label{fig:SetupWithQAutomorphism}
\end{figure}
Similarly what was done in \cite{ogata2021h3gmathbb}, we will define an index on the space of states that can be disentangled by a Q-automorphism. This class of automorphisms is defined as:
\begin{definition}\label{def:QAut}
Take $\alpha\in\Aut{\AA}$. We say that $\alpha\in\QAut{\AA}$ if and only if $\forall\theta\in]0,\pi/2[$ there exists an $\alpha_L\in\Aut{\AA_L},\alpha_R\in\Aut{\AA_R},V_1\in\UU(\AA)$ and a $\Theta\in\Aut{\AA_{W(C_\theta)^c}}$\footnote{Note that our definition of $\QAut{\AA}$ is slightly different from the definition of $\textrm{QAut}(\AA)$ from \cite{ogata2021h3gmathbb} because of this vertical widening $W$.} such that
\begin{equation}
\alpha=\Ad{V_1}\circ\alpha_L\otimes\alpha_R\circ\Theta.
\end{equation}
\end{definition}
We will often write $\alpha_0$ to mean $\alpha_L\otimes\alpha_R$. In this paper, we will consider states that satisfy the following property (see figure \ref{fig:SetupWithQAutomorphism} for the support of the automorphisms):
\begin{restatable}{assumption}{assumptionOne}\label{assumption}
Let $\omega\in\PP(\AA)$ be
\begin{enumerate}
\item such that there exists an automorphism $\alpha\in\QAut{\AA}$ and a product state $\omega_0\in\PP(\AA)$ satisfying
\begin{align}
\omega=\omega_0\circ\alpha.
\end{align}
\item such that there exists a $\theta\in]0,\pi/2[$ for which there exists a map, $\tilde\beta:G\rightarrow\Aut{\AA}:g\mapsto\tilde\beta_g$, satisfying
\begin{align}\label{eq:DecompositionOfBetaTilde}
\omega\circ\tilde\beta_g&=\omega&\tilde\beta_g=\Ad{V_{g,2}}\circ\eta^L_g\otimes\eta^R_g\circ\beta^U_g
\end{align}
for some $V_{g,2}\in\UU(\AA),\eta^L_g\in\Aut{\AA_{\nu^{-1}(C_\theta\cap L)}}$ and $\eta^R_g\in\Aut{\AA_{\nu(C_\theta\cap R)}}$.
\item translation invariant ($\omega\circ\tau=\omega$).
\end{enumerate}
\end{restatable}
We will also require a similar subclass of automorphisms and states on the quasi-local $C^*$-algebra over $\ZZ$, $\AA_{L_0}$. We now define the assumption
\begin{restatable}{assumption}{assumptionOneDimensionalOne}\label{assumption1d}
Take $\phi\in\PP(\AA_{L_0})$ such that
\begin{enumerate}
\item $\phi\circ\beta_g=\phi$.
\item there exist automorphisms $\tilde\alpha_L\in\Aut{\AA_{L_0\cap L}}$, $\tilde\alpha_R\in\Aut{\AA_{L_0\cap R}}$ and a summable operator $b\in\UU(\AA_{L_0})$ such that
\begin{equation}
\phi_0=\phi\circ\Ad{b}\circ\tilde\alpha_{L}\otimes\tilde\alpha_{R}
\end{equation}
is a product state.
\end{enumerate}
\end{restatable}
We now state the result that using assumption \ref{assumption} we can define an $H^2(G,\TT)$-valued index.
\begin{theorem}\label{thrm:ExistenceFirstIndex}
For any $\AA$ satisfying the construction from section \ref{sec:QuasiLocalC*Algebra} and any choice of on-site group action $U\in\hom(G,U(\CC^d))$, there exists a map
\begin{equation}
\textrm{Index}^{\AA,U}:\{\omega\in\PP(\AA)|\omega\text{ satisfies assumption \ref{assumption}}\}\rightarrow H^2(G,\TT)
\end{equation}
that is well-defined (doesn't depend on any of the choices in assumption \ref{assumption}). This map will be consistent with conjecture \ref{conj} by which we mean that:
\begin{enumerate}
\item For any $G$ invariant and translation invariant family of interactions $\Phi\in\BB_{F_{\phi}}([0,1])$ (for some $0<\phi<1$) we have that $\textrm{Index}^{\AA,U}(\omega)=\textrm{Index}^{\AA,U}(\omega\circ\gamma^{\Phi}_{0;1})$.
\item For $\phi\in\PP(\AA_{L_0})$, any one dimensional $G$-invariant state satisfying assumption \ref{assumption1d}, the state $\omega_\phi$ as defined in definition \ref{def:InfiniteTensorProduct} satisfies $\textrm{Index}^{\AA_{L_0},U}_{1d}(\phi)=\textrm{Index}^{\AA,U}(\omega)$.
\item This index is a group homomorphism under the stacking operator. By this, we mean that
\begin{equation}
\textrm{Index}^{\AA^2,U\otimes U}(\omega_1\otimes_{\text{stack}}\omega_2)=\textrm{Index}^{\AA,U}(\omega_1)+\textrm{Index}^{\AA,U}(\omega_2).
\end{equation}
\item The index is independent on the choice of basis for the on-site Hilbert space by which we mean that for any on-site unitary $V$ we get that $\textrm{Index}^{\AA,\Ad{V^\dagger}(U)}(\omega\circ i_V)=\textrm{Index}^{\AA,U}(\omega)$.
\end{enumerate}
\end{theorem}
\begin{proof}
This statement is proven in section \ref{sec:ProofOfMainTheorems}.
\end{proof}
The assumption from which we can define the $H^1(G,\TT)$-valued index is the same one with an additional translation invariance:
\begin{restatable}{assumption}{assumptionTwo}\label{assumption:2Translations}
Let $\omega\in\PP(\AA)$ satisfy assumption \ref{assumption} with the additional property that it is also translation invariant in the other direction ($\omega\circ\nu=\omega$).
\end{restatable}
Similar to before, we also require an assumption for states on the quasi-local $C^*$-algebra over $\ZZ$.
\begin{restatable}{assumption}{assumptionOneDimensionalTwo}\label{assumption1dWithTranslation}
Let $\phi\in\PP(\AA_{L_0})$ satisfy assumption \ref{assumption1d} with the additional property that $\phi$ is translation invariant ($\phi\circ\nu=\phi$).
\end{restatable}
We are now ready to state the second main result:
\begin{theorem}\label{thrm:ExistenceSecondIndex}
For any $\AA$ satisfying the construction from section \ref{sec:QuasiLocalC*Algebra} and any choice of on-site group action $U\in\hom(G,U(\CC^d))$, there exists a map
\begin{equation}
\textrm{Index}^{\AA,U}_{2\text{ trans}}:\{\omega\in\PP(\AA)| \omega\text{ satisfies assumption \ref{assumption:2Translations}}\}\rightarrow H^1(G,\TT)
\end{equation}
that is well-defined (doesn't depend on any of the choices made in assumption \ref{assumption:2Translations}). This map will be consistent with conjecture \ref{conj2} by which we mean the following:
\begin{enumerate}
\item For any $G$ invariant family of interactions that is translation invariant in both directions $\Phi\in\BB_{F_\phi}([0,1])$ we have that $\textrm{Index}^{\AA,U}_{2\text{ trans}}(\omega)=\textrm{Index}^{\AA,U}_{2\text{ trans}}(\omega\circ\gamma^\Phi_{0;1})$.
\item For $\phi\in\PP(\AA_{L_0})$, any one dimensional $G$-invariant and translation invariant state satisfying assumption \ref{assumption1d}, the state $\omega_\phi$ as defined in \ref{def:InfiniteTensorProduct}, satisfies $\textrm{Index}^{\AA_{L_0},U}_{1d\text{ trans}}(\phi)=\text{Index}^{\AA,U}_{2\text{ trans}}(\omega_\phi)$.
\item This index is a group homomorphism under the stacking operator by which we mean that
\begin{equation}
\textrm{Index}_{\text{2 trans}}^{\AA^2,U\otimes U}(\omega_1\otimes_{\text{stack}}\omega_2)=\textrm{Index}_{\text{2 trans}}^{\AA,U}(\omega_1)+\textrm{Index}_{\text{2 trans}}^{\AA,U}(\omega_2).
\end{equation}
\item The index is independent of the choice of basis for the on-site Hilbert space. By this we mean that, for any on-site unitary $V$, we get that $\textrm{Index}^{\AA,\Ad{V^\dagger}(U)}_{\text{2 trans}}(\omega\circ i_V) =\textrm{Index}^{\AA,U}_{\text{2 trans}}(\omega)$.
\end{enumerate}
\end{theorem}
\begin{proof}
This statement is also proven in subsection \ref{sec:ProofOfMainTheorems}.
\end{proof}
\subsection{SRE implies previous assumptions}\label{sec:Results_1}
The assumptions in the previous subsection are rather technical. However, it turns out that any SRE state, with some additional symmetries, naturally satisfies these assumptions. The precise statements and proofs are formulated in section \ref{sec:ProofOfMainResult1} but we will describe them in words here.
\\\\
As is shown in appendix \versionDifference{\ref{sec:properties-of-locally-generated-automorphisms-2d}}{C of \cite{jappens2023spt}}, which is based on the work in \cite{ogata2021h3gmathbb}, for any one parameter family of interactions $\Phi\in\BB_{F_\phi}([0,1])$, we have that $\gamma^\Phi_{0;1}\in\QAut{\AA}$. This implies the following. Take any SRE state $\omega$ (see definition \ref{def:sre}), with entangler $\gamma^\Phi_{0;1}$, and product state $\omega_0$ such that $\omega=\omega_0\circ \gamma^\Phi_{0;1}$. We can simply define the $\alpha$ from assumption \ref{assumption} to be equal to this $\gamma^\Phi_{0;1}$. Similarly, in \cite{ogata2021h3gmathbb} it has been shown that if this state has an additional on-site symmetry, we can use the $\Phi$ and $\omega_0$ to construct some $\tilde\beta_g$ that can be decomposed like in equation \eqref{eq:DecompositionOfBetaTilde} for any angle.
\\\\
It should also be said that we use the same definition of SRE (with the same $F$-function) for states over the quasi-local $C^*$-algebra over $\ZZ$, $\AA_{L_0}$. This is because we will use the 1D SRE states to create translation-invariant 2D SRE states. Since the $F$-norm of a sum of disjoint interactions has an $F$-norm given by the highest of the $F$-norms of its sub-interactions, this means that to ensure that the resulting state has a well-defined index, we will need a similar $F$-norm and not something weaker.
\\\\
Additionally, it turns out that the indices that are defined in the last subsection are independent of the choice of representative of the equivalence classes introduced in \ref{sec:StableEquivalenceClasses}.
\\\\
All in all, we will show the following theorem:
\begin{theorem}\label{lem:IndicesConstantOnStableEquivalenceClasses}
Take $(\omega,U)\in S_0$ (see subsection \ref{sec:StableEquivalenceClasses}) for the algebra $\AA$. The following statements now hold:
\begin{enumerate}
\item $\textrm{Index}^{\AA,U}_{\text{no trans}}(\omega)$ is well defined and independent on the choice of representative of $\expval{\omega}_\sim$.
\item If additionally, $(\omega,U)\in S_1$, $\textrm{Index}^{\AA,U}(\omega)$ is also well defined and independent on the choice of representative of $\expval{\omega}_\sim^1$.
\item If instead, $(\omega,U)\in S_2$, $\textrm{Index}^{\AA,U}(\omega\circ\mu)$ is well defined and independent on the choice of representative of $\expval{\omega}_\sim^2$.
\item If additionally, $(\omega,U)\in S_3$, $\textrm{Index}^{\AA,U}_{\textrm{2 trans}}(\omega)=\textrm{Index}^{\AA,U}_{\textrm{2 trans}}(\omega\circ\mu)$ is well defined and independent on the choice of representative of $\expval{\omega}_\sim^3$.
\end{enumerate}
\end{theorem}
\begin{proof}
This is shown in section \ref{sec:ProofOf:lem:IndicesConstantOnStableEquivalenceClasses}.
\end{proof}
\subsection{Comparison with \texorpdfstring{\cite{ogata2021h3gmathbb}}{}}\label{sec:SomeRemarks}
The first thing we would like to remark on is that in \cite{ogata2021h3gmathbb}, a different equivalence class on states is used. First of all the set of states considered is a priori different. Namely, for any state $\psi\in \PP(\AA)$, we define two different conditions
\begin{enumerate}
\item There exists a $\Phi\in\PP_{\text{SL}}$\footnote{This is defined in \cite{ogata2021h3gmathbb} but it essentially means bounded interaction that is connected to a trivial (without overlapping terms) interaction.} such that $\psi$ is the unique gapped groundstate of $\Phi$.
\item $\psi$ is an SRE state.
\end{enumerate}
However, in theorem 5.1 of \cite{ogata2021h3gmathbb} it is proven that the first item implies the second item. If one then looks at the definition of the index there, one could as well have started from the second condition. This is precisely what we did in this paper. As a side note, one should also be able to prove that the second item implies the first item by using theorem D.5 of \cite{ogata2021h3gmathbb} with $\mathcal{K}_t$ the disentangler and $\Phi$ a gapped interaction that has the product state as its ground state. However, we won't work this out explicitly in this paper.\\\\
When we add the group, the story changes considerably. Let us define the two different equivalence classes. To this end, let $\psi_1$ and $\psi_2$ be two (pure) $G$-invariant states that are unique gapped groundstates of $\Phi_0$ and $\Phi_1\in\PP_{\text{SL},\beta}$ respectively. The following two conditions define different equivalence classes:
\begin{enumerate}
\item There exists a $G$-invariant, bounded path of gapped interactions $\lambda\mapsto\tilde\Phi(\lambda)$ (see \cite{ogata2021h3gmathbb} for precise definitions) such that $\psi_1$ and $\psi_2$ are unique gapped groundstates of $\tilde{\Phi}(0)$ and $\tilde{\Phi}(1)$ respectively.
\item There exists a $G$-invariant LGA, $\gamma^\Psi_{0;1}$ such that $\psi_1\circ\gamma^H_{0;1}=\psi_2$.
\end{enumerate}
A priori those two conditions are not equivalent. However, in \cite{ogata2021h3gmathbb} it is proven that the first equivalence implies the second one. The proof that equivalent states have the same index only uses the second condition. This means that one could also have taken the second equivalence condition as the starting point. This is exactly what we do in this paper. One should also be able to show that the second condition implies the first one using a similar construction as in the above remark without the group and averaging the resulting interaction over the group (where one then has to use that a finite group has a normalized Haar measure).\\\\
There were two things that are in theorems \ref{thrm:ExistenceFirstIndex} and \ref{thrm:ExistenceSecondIndex} but were not discussed in \cite{ogata2021h3gmathbb}. This is the part that proves that the index is a group homomorphism under stacking and the part that the index is independent of the choice of basis for the on-site Hilbert space. However, on inspection of the arguments used in this paper one can conclude that these also hold for the $H^3$-valued index.\\\\
All in all, we have provided a proof that the work done in \cite{ogata2021h3gmathbb} also implies the following theorem:
\begin{theorem}\label{thrm:ExistenceOriginalIndex}
For any $\AA$ satisfying the construction from section \ref{sec:QuasiLocalC*Algebra} and any choice of on-site group action $U\in\hom(G,U(\CC^d))$, there exists a map
\begin{equation}
\textrm{Index}^{\AA,U}_{\text{no trans}}:\{\omega\in\PP(\AA)| \omega\text{ is SRE and }G\text{-invariant}\}\rightarrow H^3(G,\TT)
\end{equation}
that is well-defined (doesn't depend on the choice of disentangler). This map will satisfy:
\begin{enumerate}
\item For any $G$ invariant family of interactions $\Phi\in\BB_{F_\phi}([0,1])$ we have that
\begin{equation}
\textrm{Index}^{\AA,U}_{\text{no trans}}(\omega)=\textrm{Index}^{\AA,U}_{\text{no trans}}(\omega\circ\gamma^\Phi_{0;1}).
\end{equation}
\item This index is a group homomorphism under the stacking operator by which we mean that
\begin{equation}
\textrm{Index}_{\text{no trans}}^{\AA^2,U\otimes U}(\omega_1\otimes_{\text{stack}}\omega_2)=\textrm{Index}_{\text{no trans}}^{\AA,U}(\omega_1)+\textrm{Index}_{\text{no trans}}^{\AA,U}(\omega_2).
\end{equation}
\item The index is independent of the choice of basis for the on-site Hilbert space by which we mean that for any on-site unitary $V$ we get that
\begin{equation}
\textrm{Index}^{\AA,\Ad{V^\dagger}(U)}_{\text{no trans}}(\omega\circ i_V) =\textrm{Index}^{\AA,U}_{\text{no trans}}(\omega).
\end{equation}
\end{enumerate}
\end{theorem}
\section{Translation invariance in one dimension}\label{sec:OneDimensionalIndices}
Let $\AA_{L_0}$ be the quasi-local $C^*$ algebra defined on the one-dimensional lattice. Let $U_i\in\hom(G,\UU(\AA_i))$ (for $i\in\ZZ$) be the on-site group action. Let $\beta_g$ be again so that for each finite $I\subset \ZZ$, $\beta_g^I=\Ad{\bigotimes_{i\in I}U_i(g)}$. In this section, we will look at states satisfying the split property. We say that $\omega\in\PP(\AA_{L_0})$ satisfies the split property iff. it is quasi equivalent to $\omega|_{L}\otimes\omega|_{R}$. This implies that there exists a GNS triple of $\omega$, $(\HH,\pi,\Omega)$ that is of the form $\HH=\HH_L\otimes\HH_R$, $\pi=\pi_L\otimes\pi_R$. We will denote the space of pure states satisfying the split property by $\mathcal{S}\PP(\AA)$. Now let us additionally ask that $\omega$ is invariant under the group action ($\omega\circ\beta_g=\omega$). The following now holds:
\begin{lemma}
There exist maps $u_\sigma:G\rightarrow \UU(\HH_\sigma)$ (for all $\sigma\in\{L,R\}$) satisfying
\begin{align}
\Ad{u_\sigma(g)}\circ\pi_\sigma&=\pi_\sigma\circ\beta_g^\sigma&u_L(g)\otimes u_R(g)\Omega&=\Omega.
\end{align}
They are unique up to a $G$-dependent phase. Furthermore, there exists a 2-cochain $C:G^2\rightarrow U(1)$ that satisfies
\begin{align}
u_R(g)u_R(h)u_R(gh)^{\dagger}&=C(g,h)\id_{H_R}&u_L(g)u_L(h)u_L(gh)^{\dagger}&=C(g,h)^{-1}\id_{H_L}.
\end{align}
Its second group cohomology class is independent of the choice of GNS triple or the choice of (a $G$-dependent) phase in $u_R(g)$. This index is invariant under locally generated automorphisms generated by $G$-invariant interactions.
\end{lemma}
\begin{proof}
See \cite{ogata2019classification}.
\end{proof}
The cohomology class of this 2-cochain is called the one-dimensional SPT index. Now let us assume additionally (on top of the split property and the $G$-invariance) that $\omega$ be translation invariant. To this end, let $\nu$ be the automorphism that translates $\BB$ by one site to the right. We assume that $\omega\circ\nu=\omega$. The following now holds:
\begin{lemma}
There exists a unique $w\in\UU(\HH)$ such that
\begin{align}
\Ad{w}\circ\pi&=\pi\circ\nu&w\Omega&=\Omega.
\end{align}
\end{lemma}
\begin{proof}
Since $\omega\circ\nu=\omega$, we get that $(\HH,\pi\circ\nu,\Omega)\ue (\HH,\pi,\Omega)$. The uniqueness of the GNS triple now implies the existence of this $w$. Its uniqueness follows from the irreducibility of $\pi$.
\end{proof}
We can use this to define an additional 1d index for translation invariant states. To do this, we will need to use the finiteness of the group explicitly. We will use one particular property of this, namely that finite groups have discrete U(1) representations. By this we mean the following:
\begin{lemma}\label{lem:FiniteGroupsHaveDiscreteU(1)Representations}
Let $G$ be a finite group. Let $\alpha:[0,1]\rightarrow\hom(G,U(1)):\lambda\mapsto \alpha_\lambda$ be a map such that $\lambda\mapsto\alpha_\lambda(g)$ is continuous for all $g\in G$. If $\alpha_0(g)=1$ for all $g\in G$ then $\alpha_\lambda(g)=1$ for all $g\in G$ and all $\lambda\in[0,1]$.
\end{lemma}
\begin{proof}
Take $\alpha$ as above with $\alpha_0(g)=1$ for all $g\in G$, we will prove that $\alpha_\lambda(g)=1$ for all $g\in G$ and all $\lambda\in[0,1]$. To do this, let $n$ be the order of $G$. It follows from Lagrange's theorem that $g^n=\id_G$ for all $g\in G$. This implies that there exists a unique ($\lambda$ and $g$ dependent) $k\in\NN\cap [0,n-1]$ such that $\alpha_\lambda(g)=\exp(2\pi ik/n)$. Since for any fixed $g\in G$, $\alpha_\lambda(g)$ has to be continuously connected to $1$, we deduce that $k=0$ and hence the result follows.
\end{proof}
\begin{lemma}
There exists a (unique) $\alpha\in\hom(G,U(1))$ satisfying that
\begin{equation}
\pi(U_{-1}(g)) (\id_{\HH_L}\otimes u_R(g))=\alpha(g)w^\dagger(\id_{\HH_L}\otimes u_R(g)) w.
\end{equation}
This index is invariant under locally generated automorphisms generated by one-parameter families of interactions in $\BB_{F_\phi}([0,1])$ (with $F_\phi$ as presented in \eqref{eq:OurFFunction}) that are both $G$ and translation invariant.
\end{lemma}
\begin{proof}
The fact that $\alpha$ exists follows from the fact that $\pi$ is irreducible and combined with the fact that
\begin{equation}
\Ad{\pi(U_{-1}(g)) (\id_{\HH_L}\otimes u_R(g))}\circ\pi=\Ad{w^\dagger(\id_{\HH_L}\otimes u_R(g)) w}\circ\pi=\pi\circ\beta_g^{[-1,\infty[}.
\end{equation}
The fact that $\alpha$ is a $U(1)-$representation follows from the fact that $u_R$ is the lift of a projective representation. Suppose that $u_R(g)u_R(h)=C(g,h)u_R(gh)$ then
\begin{equation}
\pi(U_{-1}(g)) (\id_{\HH_L}\otimes u_R(g))\pi(U_{-1}(h)) (\id_{\HH_L}\otimes u_R(h))=C(g,h)\pi(U_{-1}(gh)) (\id_{\HH_L}\otimes u_R(gh))
\end{equation}
on the one hand whereas
\begin{equation}
w^\dagger(\id_{\HH_L}\otimes u_R(g)) ww^\dagger(\id_{\HH_L}\otimes u_R(h)) w=C(g,h)w^\dagger(\id_{\HH_L}\otimes u_R(gh)) w.
\end{equation}
These two equations can only be consistent if $\alpha(g)\alpha(h)=\alpha(gh)$. The proof that this is independent of the choice of GNS triple is straightforward. Now we need to show that this index is invariant under LGA's generated by $G$-invariant interactions. To this end let $F_\phi$ be our F-function from equation \eqref{eq:OurFFunction}. Let $\Phi\in\BB_{F_\phi}([0,1])$ be a $G$-invariant, translation invariant interaction. For simplicity of notation let $\Phi_{\text{split}}=\Phi_{\nu^{-1}(L)}+\Phi_{\nu(R)}$. Let $\lambda\in[0,1]\mapsto A_\lambda\in\UU(\AA)$ be a norm continuous one-parameter family such that
\begin{align}\label{eq:DefinitionSplitting1DAppendix}
\gamma^\Phi_{0;\lambda}&=\Ad{A_\lambda}\circ\gamma^{\Phi_{\text{split}}}_{0;\lambda}&A_0&=\id_\AA.
\end{align}
and define $A\defeq A_1$. This exists because of lemma \versionDifference{\ref{lem:PropertiesLocallyGeneratedAutomorphisms1d}}{B.1. of \cite{jappens2023spt}}. By construction $(\HH,\pi\circ\gamma^{\Phi_{\text{split}}}_{0;1},\pi(A^\dagger)\Omega)$ is a GNS triple of $\omega\circ\gamma^\Phi_{0;1}$. Let $\tilde{w}\defeq \pi(A^\dagger)w\pi(A)$ then $\tilde{\alpha}(g)\defeq \pi(U_{-1}(g))u_R(g)\tilde{w}^\dagger u_R(g)^\dagger \tilde{w}$ is the index of $\omega\circ\gamma^\Phi_{0;1}$. Putting the $A$'s to the front and inserting the old index gives
\begin{equation}
\tilde{\alpha}(g)=\alpha(g)w^\dagger \pi\circ\beta_g^R(\nu(A^\dagger)A)\pi(A^\dagger\nu(A))w.
\end{equation}
This shows that we conclude the proof if we can show that $\beta_g^R(\nu(A^\dagger)A)=\nu(A^\dagger)A$. We will do this proof in two steps. The first step is that we prove that $\Ad{\beta_g^R(\nu(A^\dagger)A)}=\Ad{\nu(A^\dagger)A}$. We use the first equation of \eqref{eq:DefinitionSplitting1DAppendix} and obtain
\begin{align}
\Ad{\beta_g^R(\nu(A^\dagger)A)}=\stkout{\beta_g^R}\circ\gamma^{\nu(\Phi_{\text{split}})}_{0;1}\circ\stkout{\nu\circ\nu^{-1}}\circ\gamma^{\Phi_{\text{split}}}_{1;0}\circ\stkout{(\beta_g^R)^{-1}}=\Ad{\nu(A^\dagger)A}.
\end{align}
This shows that there exists some $\alpha'\in\hom(G,U(1))$ such that $\alpha'(g)=\beta_g^R(\nu(A^\dagger)A)(A^\dagger \nu(A))$. However since this has to hold for each $\lambda\in[0,1]$, we can define for each $\lambda$ some $\alpha_\lambda\in\hom(G,U(1))$ through $\alpha_\lambda(g)=\beta_g^R(\nu(A^\dagger_\lambda)A_\lambda)(A^\dagger_\lambda \nu(A_\lambda))$. This implies that $\alpha'(g)=\alpha_1(g)$ has to be connected to $\alpha_0(g)=1$. Now we will use that the $U(1)$ representations of a finite group are discrete. More specifically we will use lemma \ref{lem:FiniteGroupsHaveDiscreteU(1)Representations}. This implies that $\alpha'(g)=1$ for all $g\in G$.
\end{proof}
All together we constructed a proof of the following theorem:
\begin{theorem}
There exist maps
\begin{align}
\textrm{Index}_{1d}&:\{\omega\in\mathcal{S}\PP(\AA)|\omega\circ\beta_g=\omega\}\rightarrow H^2(G,\TT)\\
\nonumber
\textrm{Index}_{1d\text{ trans}}&:\{\omega\in\mathcal{S}\PP(\AA)|\omega\circ\beta_g=\omega\text{ and }\omega\circ\nu=\omega\}\rightarrow H^1(G,\TT)\cong \hom(G,\TT).
\end{align}
For any $G-$invariant family of interactions $\Phi\in\BB_{F}([0,1])$, we have that $\textrm{Index}_{1d}(\omega)=\textrm{Index}_{1d}(\omega\circ\gamma^\Phi_{0;1})$. For any $G-$invariant family of interactions $\Phi'\in\BB_{F}([0,1])$ that is also translation invariant, we have that $\textrm{Index}_{1d\text{ trans}}(\omega)=\textrm{Index}_{1d\text{ trans}}(\omega\circ\gamma^{\Phi'}_{0;1})$.
\end{theorem}
\section{Cone and translation operators}\label{sec:ConeAndTranslationOperators}
\begin{figure}
\centering
\def\s{0.4}
\resizebox{0.21\textwidth}{!}{%
\input{Figures/Cone.tex}}
$\quad$
\def\s{0.4}
\resizebox{0.21\textwidth}{!}{%
\input{Figures/Cone_W.tex}}
$\quad$
\def\s{0.4}
\resizebox{0.21\textwidth}{!}{%
\input{Figures/Cone_Nu.tex}}
$\quad$
\def\s{0.4}
\resizebox{0.24\textwidth}{!}{%
\input{Figures/Cone_W_Nu.tex}}
\caption{This is a graphical depiction of the support of the automorphisms $\xi_L$ and $\xi_R$ with respect to $\Theta$ in the definitions of $\textrm{Cone}_{\sigma}(\alpha_0,\theta)$, $\textrm{Cone}_{\sigma}^W(\alpha_0,\theta)$, $\textrm{Cone}_{\nu^\sigma(\sigma)}(\alpha_0,\theta)$ and $\textrm{Cone}_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta)$ respectively.}
\label{fig:ConeOperators}
\end{figure}
In this section, we will fix certain objects that we will later on use to define an $H^2(G,\TT)-$valued index for states satisfying assumption \ref{assumption} and an $H^1(G,\TT)-$valued index for states satisfying assumption \ref{assumption:2Translations}. To this end, let $\omega\in\PP(\AA)$ satisfy assumption \ref{assumption}. Fix a product state $\omega_0$ and an $\alpha\in\QAut{\AA}$ such that $\omega=\omega_0\circ\alpha$. Fix $(\HH_0=\HH_L\otimes\HH_R,\pi_0=\pi_L\otimes\pi_R,\Omega_0)$, a GNS triple (see theorem 2.3.16 in \cite{bratteli1979operator}) of $\omega_0$ where ($\forall\sigma\in\{L,R\}$) $\pi_\sigma:\AA_\sigma\rightarrow\BB(\HH_\sigma)$ is a GNS representation of the restriction of $\omega_0$ to $\AA_\sigma$. We also fix, $V_1$, $\alpha_0=\alpha_L\otimes\alpha_R$ and $\Theta$ as a choice of decomposition for $\alpha$ such that $\Theta$ and $\eta_g$ commute (see figure \ref{fig:SetupWithQAutomorphism}). Because we will be working with states that are translation invariant, it makes sense to define the translation action on the GNS space of $\omega_0$:
\begin{lemma}\label{lem:Definition_v_And_w}
There exists a unique $v\in\UU(\HH_0)$ such that
\begin{align}
\Ad{v}\circ\pi_0&=\pi_0\circ\alpha_0\circ\Theta\circ\tau\circ\Theta^{-1}\circ\alpha_0^{-1}&&\text{and}&\pi_0(V_1)v\pi_0(V_1^\dagger)\Omega_0&=\Omega_0.
\end{align}
If additionally, $\omega$ satisfies assumption \ref{assumption:2Translations}, there exists a unique $w\in\UU(\HH_0)$ such that
\begin{align}
\Ad{w}\circ\pi_0&=\pi_0\circ\alpha_0\circ\Theta\circ\nu\circ\Theta^{-1}\circ\alpha_0^{-1}&&\text{and}&\pi_0(V_1)w\pi_0(V_1^\dagger)\Omega_0&=\Omega_0.
\end{align}
\end{lemma}
\begin{proof}
We only do the first part as the second part is analogous. Since $\omega\circ\tau=\omega$ we get by the uniqueness of the GNS triple (see Corollary 2.3.17 and Theorem 2.3.19 from \cite{bratteli1979operator}) that there exists a unique $\tilde{v}\in\UU(\HH_0)$ satisfying
\begin{align}
\Ad{\tilde{v}}\circ\pi_0\circ\alpha&=\pi_0\circ\alpha\circ\tau&\tilde{v}\Omega_0&=\Omega_0.
\end{align}
Since $\alpha=\Ad{V_1}\circ\alpha_0\circ\Theta$ we get that
\begin{align}
\Ad{\pi_0(V_1^\dagger)\tilde{v}\pi_0(V_1)}\circ\pi_0\circ\alpha_0\circ\Theta&=\pi_0\circ\alpha_0\circ\Theta\circ\tau&\tilde{v}\Omega_0&=\Omega_0.
\end{align}
Choosing $v=\pi_0(V_1^\dagger)\tilde{v}\pi_0(V_1)$ concludes the proof.
\end{proof}
We now define a subgroup of $\UU(\HH_0)$ that includes the representations of cone automorphisms (see figure \ref{fig:ConeOperators} for a graphical depiction of the supports of $\xi$):
\begin{definition}\label{def:ConeOperators}
Take $0<\theta<\pi/2$, $\alpha_L\in\Aut{\AA_{L}}$, $\alpha_R\in\Aut{\AA_{R}}$ and $\alpha_0\defeq \alpha_L\otimes\alpha_R$. Take $\sigma\in\{L,R\}$ and $x\in\UU(\HH_{\sigma})\otimes\id_{\HH_{\ZZ^2/\sigma}}$ then we say that $x$ is a cone operator on $\sigma$ (or in short $x\in\textrm{Cone}_{\sigma}(\alpha_0,\theta)$) if and only if there exists a $\xi\in\Aut{\AA_{W(C_\theta)\cap\sigma}}$ such that
\begin{equation}
\Ad{x}\circ\pi_0\circ\alpha_0=\pi_0\circ\alpha_0\circ\xi.
\end{equation}
$\textrm{Cone}_\sigma(\alpha_0,\theta)$ is a subgroup of $\UU(\HH_\sigma)\otimes\id_{\ZZ^2/\sigma}$. We have that
\begin{align}\label{eq:CommutantPropertyCones}
\textrm{Cone}_R(\alpha_0,\theta)&\subseteq\textrm{Cone}_L(\alpha_0,\theta)'&\textrm{Cone}_L(\alpha_0,\theta)&\subseteq\textrm{Cone}_R(\alpha_0,\theta)'.
\end{align}
If additionally $\xi\in\Aut{\AA_{C_\theta\cap\sigma}}$, $\xi\in\Aut{\AA_{\nu^\sigma(W(C_\theta)\cap\sigma)}}$ or $\xi\in\Aut{\AA_{\nu^\sigma(C_\theta\cap\sigma)}}$ respectively, we will say that $x\in\textrm{Cone}_\sigma^W(\alpha_0,\theta)$, $x\in\textrm{Cone}_{\nu^\sigma(\sigma)}(\alpha_0,\theta)$ or $x\in\textrm{Cone}_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta)$ respectively.
\end{definition}
\begin{proof}
The proof of equation \eqref{eq:CommutantPropertyCones} just follows from the fact that we defined $\textrm{Cone}_\sigma(\alpha_0,\theta)$ such that
\begin{align}
\textrm{Cone}_L(\alpha_0,\theta)&\subseteq \UU(\HH_L)\otimes\id_{\HH_R}&\textrm{Cone}_R(\alpha_0,\theta)&\subseteq \id_{\HH_L} \otimes \UU(\HH_R).
\end{align}
\end{proof}
We will also define a generalization of this. We will define a subgroup of $\UU(\HH_0)$ that includes both the group $\pi_0\circ\alpha_0\circ\Theta(\UU(\AA_R))$ and the representations of cone automorphisms:
\begin{definition}
Take $0<\theta<\pi/2$, $\alpha_L\in\Aut{\AA_{L}}$, $\alpha_R\in\Aut{\AA_{R}}$ and $\Theta\in\Aut{\AA_{W(C_\theta)^c}}$. Take $\sigma\in\{L,R\}$ and take $x\in\UU(\HH_0)$ then we say that $x$ is an inner after cone operator on $\sigma$ (or in short $x\in \IAC_\sigma(\alpha_0,\theta,\Theta)$) if there exists an $A\in\UU(\AA_\sigma)$ and a $y\in\textrm{Cone}_\sigma(\alpha_0,\theta)$ such that
\begin{equation}
x=\pi_0\circ\alpha_0\circ\Theta(A)y.
\end{equation}
$\IAC_\sigma$ is a subgroup of $\UU(\HH_0)$. We get that
\begin{align}\label{eq:CommutantProperty}
\IAC_R(\alpha_0,\theta,\Theta)&\subseteq\IAC_L(\alpha_0,\theta,\Theta)'&\IAC_L(\alpha_0,\theta,\Theta)&\subseteq\IAC_R(\alpha_0,\theta,\Theta)'.
\end{align}
If, additionally, $y\in \textrm{Cone}_\sigma^W(\alpha_0,\theta)$ we will say that $x\in \IAC_\sigma^W(\alpha_0,\theta,\Theta)$. If $A\in\UU(\AA_{\nu^\sigma(\sigma)})$ and $y\in \textrm{Cone}_{\nu^\sigma(\sigma)}(\alpha_0,\theta)$, we say that $x\in\IAC_{\nu^\sigma(\sigma)}(\alpha_0,\theta,\Theta)$. If $A\in\UU(\AA_{\nu^\sigma(\sigma)})$ and $y\in \textrm{Cone}_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta)$, we say that $x\in\IAC_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta,\Theta)$.
\end{definition}
\begin{proof}
Take $u_L\in\IAC_L(\alpha_0,\theta,\Theta)$ and $u_R\in\IAC_R(\alpha_0,\theta,\Theta)$ arbitrary. Take $A_\sigma\in\UU(\AA_\sigma)$ and $v_\sigma\in\textrm{Cone}_\sigma(\alpha_0,\theta)$ (for $\sigma\in\{L,R\}$) such that $u_\sigma=\pi_0\circ\alpha_0\circ\Theta(A_\sigma)v_\sigma$. We have to prove that $[u_L,u_R]=0$. To do this, we need three things. First of all, by construction, we get that $[A_L,A_R]=0$. Secondly, we showed in \ref{eq:CommutantPropertyCones} that $[v_L,v_R]=0$. We now only have to show that $[\pi_0\circ\alpha_0\circ\Theta(A_L),v_R]$ (and vice versa) as using these three properties repeatedly on the expression $[u_L,u_R]$ shows that it vanishes. This property is clearly equivalent to showing that $\Ad{v_R}\circ \pi_0\circ\alpha_0\circ\Theta(A_L)=\pi_0\circ\alpha_0\circ\Theta(A_L)$. Using definition \ref{def:ConeOperators} and the fact that $\xi_R$ and $\Theta$ commute, this reduces to showing that $\xi_R(A_L)=A_L$. This is true by construction.
\end{proof}
\begin{remark}
The main reason for the introduction of the $\textrm{Cone}_\sigma^W(\alpha_0,\theta)$ and $\IAC^W_\sigma(\alpha_0,\theta,\Theta)$ subgroups is that they are still (inner after) cone operators when translated. More specifically, let $y\in\textrm{Cone}_\sigma^W(\alpha_0,\theta)$ then both $vyv^\dagger$ and $v^\dagger y v$ are elements of $\textrm{Cone}_\sigma(\alpha_0,\theta)$. The analogous statement is also true for the $\IAC$ operators. Similarly, in the case where there are two translation symmetries, we get that for $x\in\IAC_{\nu^\sigma(\sigma)}(\alpha_0,\theta)$ or $x\in\IAC_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta,\Theta)$, both $wx w^\dagger$ and $w^\dagger x w$ are in $\IAC_{\sigma}(\alpha_0,\theta,\Theta)$ or $\IAC_{\sigma}^W(\alpha_0,\theta,\Theta)$ respectively.
\end{remark}
There is a standard lemma we will often refer to:
\begin{lemma}\label{lem:SplittingOfUnitary}
Let $\AA$ and $\BB$ be arbitrary unital $C^*$-algebras. Let $(\HH_\AA,\pi_\AA)$ and $(\HH_\BB,\pi_\BB)$ be arbitrary irreducible $*$-representations on $\AA$ and $\BB$ respectively. Let $U\in\UU(\HH_\AA\otimes\HH_\BB)$ be such that there exists an $\alpha_\AA\in\Aut{\AA}$ and an $\alpha_\BB\in\Aut{\BB}$ satisfying
\begin{equation}
\Ad{U}\circ(\pi_\AA\otimes\pi_\BB)=\pi_\AA\circ\alpha_\AA\otimes\pi_\BB\circ\alpha_\BB
\end{equation}
then there exists a $U_\AA\in\UU(\HH_\AA)$ and a $U_\BB\in\UU(\HH_\BB)$ such that $U=U_\AA\otimes U_\BB$.
\end{lemma}
\begin{proof}
From the assumptions we see that $\forall A\in\AA$
\begin{equation}
\Ad{U}\circ\pi_\AA\otimes\pi_\BB(A\otimes\id)=\pi_\AA\circ\alpha_\AA(A)\otimes\id\subset \BB(\HH_\AA)\otimes\id.
\end{equation}
Since $\Ad{U}$ is continuous in weak operator topology (on $\BB(\HH_{\AA}\otimes\HH_{\BB})$), it follows that we can extend the map
\begin{equation}
\Ad{U}|_{\textrm{Im}(\pi_\AA)}:\textrm{Im}(\pi_\AA)\otimes\id\rightarrow \BB(\HH_\AA)\otimes\id
\end{equation}
to the closure in weak operator topology. By irreducibility (and the Von Neumann bicommutant theorem), we get that $\pi_\AA(\AA)''=\BB(\HH_\AA)$ and therefore we get a map
\begin{equation}
\Ad{U}|_{\BB(\HH_\AA)\otimes\id}:\BB(\HH_\AA)\otimes\id\rightarrow \BB(\HH_\AA)\otimes\id.
\end{equation}
By restriction, this gives rise to an automorphism $\tau_\AA:\UU(\HH_\AA)\rightarrow\UU(\HH_\AA)$. By Wigners theorem any automorphism of $\BB(\HH_\AA)$ is inner and therefore there exists a $U_\AA$ such that $\tau_\AA=\Ad{U_\AA}$. Doing the same on $\BB$ gives us similarly a $\tau_\BB$ and a $U_\BB$. We now get
\begin{equation}
\Ad{U}\circ(\pi_\AA\otimes\pi_\BB)=\tau_\AA\circ\pi_\AA\otimes\tau_\BB\circ\pi_\BB=\Ad{U_\AA\otimes U_\BB}\circ(\pi_\AA\otimes\pi_\BB).
\end{equation}
By the irreducibility of $\pi_\AA\otimes\pi_\BB$ we get that (up to some irrelevant phase) we need that $U=U_\AA\otimes U_\BB$ concluding the proof.
\end{proof}
Among other things, it shows that if a unitary on the GNS space of $\omega_0$ has an adjoint action that is the product of cones then it is a product of cone operators:
\begin{lemma}\label{lem:UsingIrreducibilityAndWignerTheorem}
Take $x\in\UU(\HH_0)$ such that there exist $\xi_\sigma\in\Aut{\AA_{C_\theta\cap\sigma}}$ (for $\sigma\in\{L,R\}$) satisfying
\begin{equation}
\Ad{x}\circ\pi_0\circ\alpha_0=\pi_0\circ\alpha_0\circ\xi_L\otimes\xi_R
\end{equation}
then there exist $x_\sigma\in\textrm{Cone}_\sigma(\alpha_0,\theta)$ such that $x=x_L\otimes x_R$. These are unique up to a phase.
\end{lemma}
\begin{proof}
Using lemma \ref{lem:SplittingOfUnitary}, the result follows.
\end{proof}
Following Ogata \cite{ogata2021h3gmathbb}, we now define objects using the following lemma:
\begin{lemma}\label{lem:Definition_W_And_u}
There unitaries $W_g\in\UU(\HH_0)$ and $u_{\sigma}(g,h)\in\UU(\HH_{\sigma})$ for all $g,h\in G$ and for all $\sigma\in\{L,R\}$ satisfying
\begin{align}
\nonumber
\Ad{W_g}\circ\pi_0&=\pi_0\circ\alpha_0\circ\Theta\circ\eta_g\circ\beta_g^U\circ\Theta^{-1}\circ\alpha_0^{-1}\\
\Ad{u_\sigma(g,h)}\circ\pi_\sigma&=\pi_\sigma\circ\alpha_\sigma\circ\eta_g^\sigma\circ\beta_g^{\sigma U}\circ\eta_h^{\sigma}\circ(\beta_g^{\sigma U})^{-1}\circ(\eta^\sigma_{gh})^{-1}\circ\alpha_\sigma^{-1}\\
\nonumber
u_L(g,h)\otimes u_R(g,h)&=W_gW_hW_{gh}^{-1}.
\end{align}
\end{lemma}
\begin{proof}
The result follows from the fact that assumption \ref{assumption} is sufficient to define the objects used in lemma 2.1 and definition 2.2 of \cite{ogata2021h3gmathbb}.
\end{proof}
These objects will be the starting point for our definition. Clearly the $u_\sigma(g,h)$ are elements of $\textrm{Cone}_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta)$. The $W_g$ have the following property:
\begin{lemma}\label{lem:AdjointOverConeIsInCone}
Take $\Xi^{\sigma}\in\textrm{Cone}_\sigma(\alpha_0,\theta)$ (for all $\sigma\in\{L,R\}$), then $\Ad{W_g}(\Xi^\sigma)\in\textrm{Cone}_\sigma(\alpha_0,\theta)$ (for all $g\in G$). If, more generally, we take $\Xi^\sigma\in\IAC_\sigma(\alpha_0,\Theta)$, then $\Ad{W_g}(\Xi^\sigma)\in\IAC_\sigma(\alpha_0,\Theta)$. Similarly if $\Xi^{\sigma}\in\textrm{Cone}_\sigma^W(\alpha_0,\theta)$, then $\Ad{W_g}(\Xi^\sigma)\in\textrm{Cone}_\sigma^W(\alpha_0,\theta)$. If additionally, $\Xi^{\sigma}\in\textrm{Cone}_{\nu^\sigma(\sigma)}(\alpha_0,\theta)$ or $\Xi^{\sigma}\in\textrm{Cone}_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta)$, $\Ad{W_g}(\Xi^\sigma)\in\textrm{Cone}_{\nu^\sigma(\sigma)}(\alpha_0,\theta)$ and $\textrm{Cone}_{\nu^\sigma(\sigma)}^W(\alpha_0,\theta)$ respectively.
\end{lemma}
\begin{proof}
Take $\tilde{\Xi}^\sigma$ such that $\Xi^\sigma=\tilde{\Xi}^\sigma\otimes\id_{\HH_{\sigma^c}}$. Take $\xi_\sigma\in\Aut{\AA_{W(C_\theta)\cap\sigma}}$ such that
\begin{equation}
\Ad{\tilde\Xi^\sigma}\circ\pi_\sigma\circ\alpha_\sigma=\pi_\sigma\circ\alpha_\sigma\circ \xi_\sigma.
\end{equation}
We have that
\begin{equation}
\Ad{\Ad{W_g}(\Xi^R)}\circ\pi_0\circ\alpha_0\circ\Theta=\pi_0\circ\alpha_0\circ\Theta\circ\zeta_{g,R}
\end{equation}
where
\begin{equation}
\zeta_{g,\sigma}\defeq \eta_g\circ\beta_g^{U}\circ\xi_\sigma\circ(\beta_g^{U})^{-1}\circ\eta_g^{-1}.
\end{equation}
Since $\zeta_{g,\sigma}\in\Aut{\AA_{C_\theta}\cap\AA_{\sigma}}$ we get that
\begin{equation}
\Ad{\Ad{W_g}(\Xi^R)}\circ\pi_0\circ\alpha_0=\pi_L\circ\alpha_L\otimes\pi_R\circ\alpha_R\circ\zeta_{g,R}.
\end{equation}
Using lemma \ref{lem:UsingIrreducibilityAndWignerTheorem} there exists a $Z_{g,R}\in\UU(\HH_R)$ satisfying that $\Ad{W_g}(\Xi^R)=\id_{\HH_L}\otimes Z_{g,R}$. To show the second result we only need to observe that for any $A\in\UU(\AA_R)$ we get that
\begin{align}
\Ad{W_g}\left(\pi_0\circ\alpha_0\circ\Theta(A)\Xi_R\right)&=\Ad{W_g}\circ\pi_0\circ\alpha_0\circ\Theta(A)\Ad{W_g}(\Xi_R)\\
\nonumber
&=\pi_0\circ\alpha_0\circ\Theta\circ\xi_R(A)\Ad{W_g}(\Xi_R).
\end{align}
By the previous result, this is clearly in $\IAC_R(\alpha_0,\theta,\Theta)$ concluding the proof.
\end{proof}
We now have to define two more objects (remember that $v$ was defined in lemma \ref{lem:Definition_v_And_w}):
\begin{lemma}\label{lem:Definition_K}
There exist $K_g^{L}\in\textrm{Cone}_{\nu^L(L)}(\alpha_0,\theta)$ and $K_g^{R}\in\textrm{Cone}_{\nu^R(R)}(\alpha_0,\theta)$ such that
\begin{equation}
v^\dagger W_g v W_g^\dagger=K_g^L\otimes K_g^R=K_g
\end{equation}
and they are unique (up to a phase). They satisfy the identity
\begin{equation}
\Ad{K^R_g}\circ\pi_0=\pi_0\circ \alpha_0\circ \tau^{-1}\circ \eta_g^R\circ\beta_g^{RU}\circ\tau\circ(\beta_g^{RU})^{-1}\circ(\eta_g^{R})^{-1}\circ\alpha_0^{-1}.\quad\footnote{Observe in particular that $\Theta$ has cancelled out}
\end{equation}
\end{lemma}
\begin{proof}
By some straightforward calculation, we have that
\begin{align}
\Ad{K_g}\circ\pi_0&=\Ad{v^\dagger W_g v W_g^\dagger}\circ\pi_0\\
\nonumber
&=\bigotimes_{\sigma=L,R}\pi_\sigma\circ\alpha_\sigma\circ\tau^{-1}\circ \eta_g^\sigma\circ\beta_g^{\sigma U}\circ\tau\circ(\beta_g^{\sigma U})^{-1}\circ(\eta_g^{\sigma})^{-1}\circ\alpha_\sigma^{-1}.
\end{align}
Using lemma \ref{lem:UsingIrreducibilityAndWignerTheorem} concludes the proof that these unitaries exist and are unique up to a $G-$dependent phase.
\end{proof}
If, additionally, $\omega$ satisfies assumption \ref{assumption1dWithTranslation}, we can use these objects to define $b^\sigma_g$:
\begin{lemma}
There exist a $b_g^L\in\textrm{Cone}_{\nu^{-1}(L)}^W(\alpha_0,\theta)$ and a $b_g^R\in\textrm{Cone}_{R}^W(\alpha_0,\theta)$ (both unique up to an exchange of a $G-$dependent phase) satisfying that
\begin{equation}
w^\dagger W_g w W_g^\dagger=b_g:=b_g^L\otimes b_g^R.
\end{equation}
It will satisfy
\begin{equation}\label{eq:automorphismBelongingTo_b}
\Ad{b_g^\sigma\otimes\id_{\HH_{\ZZ^2/\sigma}}}\circ\pi_0\circ\alpha_0=\pi_0\circ\alpha_0\circ\nu^{-1}\circ\eta_g^\sigma\circ\nu\circ(\eta_g^\sigma)^{-1}.
\end{equation}
\end{lemma}
\begin{proof}
It is easy enough to show that
\begin{equation}
\Ad{w^\dagger W_g w W_g^\dagger}\circ\pi_0=\pi_0\circ (\alpha_L\circ\nu^{-1}\circ\eta_g^L\circ\nu\circ(\eta_g^L)^{-1}\circ\alpha_L^{-1})\otimes(\alpha_R\circ\nu^{-1}\circ\eta_g^R\circ\nu\circ(\eta_g^R)^{-1}\circ\alpha_R^{-1}).
\end{equation}
To do this one only has to use that $\beta_g^U$ commutes with $\nu$. By lemma \ref{lem:UsingIrreducibilityAndWignerTheorem} the result now follows.
\end{proof}
\section{Defining the indices}
In this section, we will use the objects defined in section \ref{sec:ConeAndTranslationOperators} to define the $H^2(G,\TT)$-valued index introduced in theorem \ref{thrm:ExistenceFirstIndex} and the $H^1(G,\TT)$-valued index introduced in theorem \ref{thrm:ExistenceSecondIndex}.
\subsection{The \texorpdfstring{$H^2(G,\TT)$}{H2}-valued index}\label{sec:DefinitionH2Index}
\begin{lemma}\label{lem:Definition2Cochain}
There exists a $C:G^2\rightarrow U(1)$ such that
\begin{equation}\label{eq:Definition2Cochain}
K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)u_
R(g,h)=C(g,h)v^\dagger u_R(g,h)v
\end{equation}
for all $g,h\in G.$
\end{lemma}
\begin{proof}
Since the GNS representation is irreducible this is equivalent to showing that the left and righthand side of equation \eqref{eq:Definition2Cochain} have the same adjoint action on the GNS representation. We first prove the result for the full tensor product. By using the definition of $u(g,h)$ we get
\begin{align}\label{eq:ProofOf:lem:Definition2CochainFirstEquation}
v^\dagger u_L(g,h)v v^\dagger u_R(g,h) v&=v^\dagger (u_L(g,h)\otimes u_R(g,h)) v =v^\dagger W_g W_h W_{gh}^{-1}v.
\end{align}
Now using the definition of $K_g$ gives:
\begin{align}
\eqref{eq:ProofOf:lem:Definition2CochainFirstEquation}&=K_gW_g v^\dagger W_h W_{gh}^{-1}v=K_gW_g K_h W_h v^\dagger W_{gh}^{-1}v\\
\nonumber
&=K_gW_g K_h W_h W_{gh}^\dagger K_{gh}^\dagger=K_gW_g K_h W_h W_{gh}^\dagger K_{gh}^\dagger W_{gh}W_h^\dagger W_g^\dagger W_gW_hW_{gh}^\dagger\\
\nonumber
&=K_g\Ad{W_g}\left(K_h\Ad{W_hW_{gh}^\dagger}\left(K_{gh}^\dagger\right)\right)u_L(g,h)\otimes u_
R(g,h).
\end{align}
Using lemma \ref{lem:AdjointOverConeIsInCone} we get that
\begin{align}
&(K_g^L\otimes K_g^R)\Ad{W_g}\left((K_h^L\otimes K_h^R)\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^L\otimes K_{gh}^R)^{-1}\right)\right)\\
\nonumber
&=K_g^L\Ad{W_g}\left(K_h^L\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^L)^\dagger\right)\right)\otimes K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)
\end{align}
concluding the proof.
\end{proof}
We the next goal is to prove that this function $C$ is a $2$-cochain. We will do this by proving that the $3$-cochain constructed in \cite{ogata2021h3gmathbb} is invariant under some substitution. More precisely, we will use:
\begin{lemma}\label{lem:3cochainIsInvariant}
The three-cochain $C'(g,h,k)$ defined through
\begin{equation}\label{eq:defintion3CochainProof2Cochain}
u_R(g,h)u_R(gh,k)u_R(g,hk)^\dagger\Ad{W_g}(u_R(h,k)^\dagger)=C'(g,h,k)\id.
\end{equation}
is invariant under the substitution
\begin{align}\label{eq:SubstitutionForProofCochain}
W_g&\rightarrow K_g W_g&u_R(g,h)&\rightarrow K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)u_
R(g,h)
\end{align}
\end{lemma}
\begin{proof}
Inserting substitution \eqref{eq:SubstitutionForProofCochain} into \eqref{eq:defintion3CochainProof2Cochain} gives
\begin{align}
&u_R(g,h)u_R(gh,k)u_R(g,hk)^\dagger\Ad{W_g}\left(u_R(h,k)^\dagger\right)\\
\rightarrow&K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)u_
R(g,h)\\
\nonumber
&K_{gh}^R\Ad{W_{gh}}\left(K_k^R\Ad{W_kW_{ghk}^\dagger}\left((K_{ghk}^R)^\dagger\right)\right)u_
R(gh,k)\\
\nonumber
&u_R(g,hk)^\dagger \Ad{W_g}\left( \Ad{W_{hk}W_{ghk}^\dagger}(K^R_{ghk})(K^R_{hk})^{\dagger} \right)(K^R_g)^\dagger\\
\nonumber
&\Ad{K_gW_g}\left(u_R(h,k)^\dagger \Ad{W_h}\left(\Ad{W_kW_{hk}^\dagger}\left(K_{hk}^R\right)(K^R_k)^\dagger\right)(K^R_h)^\dagger\right).
\end{align}
Using the fact that $W_gW_hW_{gh}^\dagger=u_L\otimes u_R(g,h)$ and lemma \ref{lem:AdjointOverConeIsInCone} (for the substitution $K_g\rightarrow K_g^R$ in the last line) one now gets
\begin{align}
=&K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)\underline{W_gW_hW_{gh}^\dagger u_L(g,h)^\dagger}\\
\nonumber
&K_{gh}^R\Ad{W_{gh}}\left(K_k^R\Ad{W_kW_{ghk}^\dagger}\left((K_{ghk}^R)^\dagger\right)\right) \underline{W_{gh}W_kW_{ghk}^\dagger u_L(gh,k)^\dagger}\\
\nonumber
&\underline{W_{ghk}W_{hk}^\dagger W_{g}^\dagger u_L(g,hk)} \Ad{W_g}\left( \Ad{W_{hk}W_{ghk}^\dagger}(K^R_{ghk})(K^R_{hk})^{\dagger} \right)\stkout{(K^R_g)^\dagger}\\
\nonumber
&\:\stkout{K^R_g}\Ad{W_g}\left(u_R(h,k)^\dagger \Ad{W_h}\left(\Ad{W_kW_{hk}^\dagger}\left(K_{hk}^R\right)(K^R_k)^\dagger\right)(K^R_h)^\dagger\right)(K^R_g)^\dagger.
\end{align}
We will now use the fact that the $u_L(g,hk)$ commutes with everything that has support only on the right. Combining this with lemma \ref{lem:AdjointOverConeIsInCone} gives
\begin{align}
=&K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)W_gW_hW_{gh}^\dagger u_L(g,h)^\dagger\\
\nonumber
&K_{gh}^R\Ad{W_{gh}}\left(K_k^R\Ad{W_kW_{ghk}^\dagger}\left((K_{ghk}^R)^\dagger\right)\right) W_{gh}W_kW_{ghk}^\dagger u_L(gh,k)^\dagger\\
\nonumber
&W_{ghk}W_{hk}^\dagger W_{g}^\dagger \Ad{W_g}\left( \Ad{W_{hk}W_{ghk}^\dagger}(K^R_{ghk})(K^R_{hk})^{\dagger} \right)\underline{u_L(g,hk)}\\
\nonumber
&\:\Ad{W_g}\left(u_R(h,k)^\dagger \Ad{W_h}\left(\Ad{W_kW_{hk}^\dagger}\left(K_{hk}^R\right)(K^R_k)^\dagger\right)(K^R_h)^\dagger\right)(K^R_g)^\dagger\\
=&K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)W_gW_hW_{gh}^\dagger u_L(g,h)^\dagger\\
\nonumber
&K_{gh}^R\Ad{W_{gh}}\left(K_k^R\Ad{W_kW_{ghk}^\dagger}\left((K_{ghk}^R)^\dagger\right)\right) W_{gh}W_kW_{ghk}^\dagger u_L(gh,k)^\dagger\\
\nonumber
&\Ad{W_{ghk}W_{hk}^\dagger W_{g}^\dagger} \left(\Ad{W_g}\left( \Ad{W_{hk}W_{ghk}^\dagger}(K^R_{ghk})(K^R_{hk})^{\dagger} \right)\right)\\
\nonumber
&\underline{u_R(g,hk)^\dagger}\Ad{W_g}\left(u_R(h,k)^\dagger \Ad{W_h}\left(\Ad{W_kW_{hk}^\dagger}\left(K_{hk}^R\right)(K^R_k)^\dagger\right)(K^R_h)^\dagger\right)(K^R_g)^\dagger.
\end{align}
Doing the same with $u_L(gh,k)^\dagger$ now gives
\begin{align}
=&K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)W_gW_hW_{gh}^\dagger u_L(g,h)^\dagger\\
\nonumber
&K_{gh}^R\Ad{W_{gh}}\left(K_k^R\Ad{W_kW_{ghk}^\dagger}\left((K_{ghk}^R)^\dagger\right)\right) \\
\nonumber
&\Ad{W_{gh}W_k\stkout{W_{ghk}^\dagger W_{ghk}}W_{hk}^\dagger W_{g}^\dagger} \left(\Ad{W_g}\left( \Ad{W_{hk}W_{ghk}^\dagger}(K^R_{ghk})(K^R_{hk})^{\dagger} \right)\right)\\
\nonumber
&\underline{u_R(gh,k)}u_R(g,hk)^\dagger\Ad{W_g}\left(u_R(h,k)^\dagger \Ad{W_h}\left(\Ad{W_kW_{hk}^\dagger}\left(K_{hk}^R\right)(K^R_k)^\dagger\right)(K^R_h)^\dagger\right)(K^R_g)^\dagger.
\end{align}
When also applying this to $u_L(g,h)^\dagger$ one gets
\begin{align}
=&K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)W_gW_hW_{gh}^\dagger (K^R_g)^\dagger\\
\nonumber
&K_{gh}^R\Ad{W_{gh}}\left(K_k^R\Ad{W_kW_{ghk}^\dagger}\left((K_{ghk}^R)^\dagger\right)\right)\\
\nonumber
&\Ad{W_{gh}W_kW_{hk}^\dagger W_{g}^\dagger} \left(\Ad{W_g}\left( \Ad{W_{hk}W_{ghk}^\dagger}(K^R_{ghk})(K^R_{hk})^{\dagger} \right)\right)\\
\nonumber
&W_{gh}W_h^\dagger W_g^\dagger \underline{u_R(g,h)} u_R(gh,k)u_R(g,hk)^\dagger\Ad{W_g}\left(u_R(h,k)^\dagger\right)\\
\nonumber
&\Ad{W_g}\left(\Ad{W_h}\left(\Ad{W_kW_{hk}^\dagger}\left(K_{hk}^R\right)(K^R_k)^\dagger\right)(K^R_h)^\dagger\right)(K^R_g)^\dagger
\end{align}
Filling in the equation for the 3-cochain (equation \eqref{eq:defintion3CochainProof2Cochain}) now gives
\begin{align}
=&\underline{C'(g,h,k)}K_g^R\Ad{W_g}\left(K_h^R\Ad{W_hW_{gh}^\dagger}\left((K_{gh}^R)^\dagger\right)\right)W_gW_hW_{gh}^\dagger \\
\nonumber
&K_{gh}^R\Ad{W_{gh}}\left(K_k^R\Ad{W_kW_{ghk}^\dagger}\left((K_{ghk}^R)^\dagger\right)\right)\\
\nonumber
&\Ad{W_{gh}W_kW_{hk}^\dagger \stkout{W_{g}^\dagger}} \left(\underline{\id}\stkout{\Ad{W_g}}\left( \Ad{W_{hk}W_{ghk}^\dagger}(K^R_{ghk})(K^R_{hk})^{\dagger} \right)\right)\\
\nonumber
&W_{gh}W_h^\dagger W_g^\dagger\Ad{W_g}\left(\Ad{W_h}\left(\Ad{W_kW_{hk}^\dagger}\left(K_{hk}^R\right)(K^R_k)^\dagger\right)(K^R_h)^\dagger\right)(K^R_g)^\dagger.
\end{align}
Fully writing out the adjoints now gives:
\begin{align}
=&C'(g,h,k)K_g^RW_gK_h^RW_hW_{gh}^\dagger (K_{gh}^R)^\dagger W_{gh}W_h^\dagger W_g^\dagger W_gW_hW_{gh}^\dagger \\
\nonumber
&K_{gh}^RW_{gh}K_k^RW_kW_{ghk}^\dagger(K_{ghk}^R)^\dagger W_{ghk}W_k^\dagger W_{gh}^\dagger \\
\nonumber
&W_{gh}W_kW_{hk}^\dagger W_{hk}W_{ghk}^\dagger K^R_{ghk} W_{ghk}W_{hk}^\dagger(K^R_{hk})^{\dagger} W_{hk}W_k^\dagger W_{gh}^\dagger\\
\nonumber
&W_{gh}W_h^\dagger W_g^\dagger W_gW_h W_kW_{hk}^\dagger K_{hk}^RW_{hk}W_k^\dagger(K^R_k)^\dagger W_h^\dagger (K^R_h)^\dagger W_g^\dagger (K^R_g)^\dagger\\
=&\id C'(g,h,k)
\end{align}
concluding the proof.
\end{proof}
\begin{lemma}
The function $C$ as defined in lemma \ref{lem:Definition2Cochain} is a 2-cochain.
\end{lemma}
\begin{proof}
Take the 3-cochain $C'$ introduced in the last lemma. It is clear that this 3-cochain is invariant under the substitution
\begin{align}
W_g&\rightarrow v^\dagger W_g v&u_R(g,h)&\rightarrow v^\dagger u_R(g,h)v.
\end{align}
If we now prove that it is also invariant under the substitution in equation \ref{eq:SubstitutionForProofCochain}, we have proved our result because using equation \eqref{eq:Definition2Cochain} we then get that
\begin{equation}
\stkout{C'(g,h,k)}=C(h,k)C(gh,k)^{-1}C(g,hk)C(g,h)^{-1}\stkout{C'(g,h,k)}
\end{equation}
proving the result. The invariance of the three cochain under this substitution is proven in lemma \ref{lem:3cochainIsInvariant}.
\end{proof}
Our translation index is now defined as
\begin{definition}\label{def:DefinitionOfTheH2ValuedIndex}
Let $C:G^2\rightarrow U(1)$ be the 2-cochain defined in \ref{lem:Definition2Cochain}. Take $\phi:G^2\rightarrow\TT$ such that $C(g,h)=\exp(i\phi(g,h))$ then we define the index as
\begin{equation}
\textrm{Index}^{\AA,U}(\theta,\tilde{\beta}_g,\eta_g,\alpha_0,\Theta,\omega,\omega_0)\defeq\expval{\phi}\in H^2(G,\TT)
\end{equation}
and (as advertised) it is only a function of the automorphisms (and the product state) not on the choice of the GNS triple of $\omega_0$ or on the choice of phases in $W_g,u_L(g,h),u_R(g,h),v,K_g^L$ and $K_g^R$.\footnote{Even though we explicitly wrote down the on-site group action $U$, this index is only dependent on $\Ad{U}$.}
\end{definition}
\begin{proof}
The construction is invariant under the choice of GNS triple since this simply amounts to an adjoint action by some unitary on every operator. Now we will show that it is invariant under the choice of phases of our operators. Clearly the 2-cochain $C$ is invariant under
\begin{align}
u_L(g,h)&\rightarrow \alpha(g)\alpha(g)\alpha(gh)^{-1}\beta(g,h)^{-1} u_L(g,h)&u_R(g,h)&\rightarrow \beta(g,h)u_R(g,h)\\
\nonumber
W_g&\rightarrow\alpha(g)W_g&v&\rightarrow \gamma v.
\end{align}
Under the transformation
\begin{align}
K_g^L&\rightarrow \delta(g)^{-1}K_g^L&K_g^R&\rightarrow \delta(g)K_g^R
\end{align}
we get $C(g,h)\rightarrow \delta(g)\delta(h)\delta(gh)^{-1}C(g,h)$ which is still in the same equivalence class concluding the proof.
\end{proof}
\subsection{The \texorpdfstring{$H^1(G,\TT)$}{H1}-valued index}\label{sec:DefinitionH1Index}
\input{Figures/Figure5}
\begin{lemma}\label{lem:DefinitionAlpha}
There exists an $\alpha:G\rightarrow U(1)$ satisfying
\begin{align}\label{eq:DefinitionOfTheH_1Index}
v^\dagger b_g^R vh_g K_g^R (b_g^R)^\dagger&=\alpha(g)w^\dagger K_g^R w&&\text{where}&h_g&\defeq\pi_0\circ\alpha_0\circ\Theta(U_{(-1,-1)}(g)).
\end{align}
\end{lemma}
\begin{proof}
We have that
\begin{align}
&\Ad{w^\dagger K_g^R w}\circ\pi_0\circ\alpha_0\circ\Theta=\pi_0\circ\alpha_0\circ\Theta\circ\nu^{-1}\circ\tau^{-1}\circ\eta_g^R\circ\beta_g^{RU}\circ\tau\circ(\beta_g^{RU})^{-1}\circ(\eta_g^R)^{-1}\circ\nu.
\end{align}
Now we will use the fact that because of translation invariance of the group action, we have that $\tau^{-1}\circ\beta_g^{RU}\circ\tau\circ(\beta_g^{RU})^{-1}=\beta_g^{RL_{-1}}$ with $L_j=\{(x,y)\in\ZZ^2|y=j\}$. This leads to
\begin{align}
&=\pi_0\circ\alpha_0\circ\Theta\circ\nu^{-1}\circ\underline{\tau^{-1}}\circ\eta_g^R\circ\tau\circ\beta_g^{R,L_{-1}}\circ(\eta_g^R)^{-1}\circ\nu\\
\nonumber
&=\Ad{\underline{v^\dagger}}\circ \pi_0\circ\alpha_0\circ\Theta\circ\nu^{-1}\circ\eta_g^R\circ\tau\circ\beta_g^{R,L_{-1}}\circ(\eta_g^R)^{-1}\circ\nu.
\end{align}
Inserting $b^R_g v v^\dagger (b^R_g)^\dagger$ now gives
\begin{equation}
=\Ad{v^\dagger\underline{b^R_g v v^\dagger (b^R_g)^\dagger}}\circ \pi_0\circ\alpha_0\circ\Theta\circ\nu^{-1}\circ\eta_g^R\circ\tau\circ\beta_g^{R,L_{-1}}\circ(\eta_g^R)^{-1}\circ\nu.
\end{equation}
Using the inverse of equation \eqref{eq:automorphismBelongingTo_b} we now get
\begin{align}
&=\Ad{v^\dagger b^R_g v }\circ \pi_0\circ\alpha_0\circ\Theta\circ\underline{\tau^{-1}\circ\eta_g^R\circ\nu^{-1}\circ\stkout{(\eta_g^R)^{-1}\circ\nu}}\circ\stkout{\nu^{-1}\circ\eta_g^R}\circ\tau\circ\beta_g^{R,L_{-1}}\circ(\eta_g^R)^{-1}\circ\nu\\
\nonumber
&=\Ad{v^\dagger b_g^R v}\circ\pi_0\circ\alpha_0\circ\Theta\circ\tau^{-1}\circ\eta_g^R\circ\tau\circ\nu^{-1}\circ\beta_g^{R,L_{-1}}\circ(\eta_g^R)^{-1}\circ\nu.
\end{align}
Now we will use the fact that $\nu^{-1}\circ\beta_g^{R,L_{-1}}\circ\nu=\Ad{U_{(-1,-1)}(g)}\circ\beta_g^{R,L_{-1}}$ to obtain
\begin{equation}
=\Ad{v^\dagger b_g^R v}\circ\pi_0\circ\alpha_0\circ\Theta\circ\tau^{-1}\circ\eta_g^R\circ\tau\circ\Ad{U_{(-1,-1)}(g)}\circ\beta_g^{R,L_{-1}}\circ\nu^{-1}\circ(\eta_g^R)^{-1}\circ\nu.
\end{equation}
Since (as you can check in figure \ref{fig:SetupForTwoTranslationsNearProof}) $\tau^{-1}(\eta_g^R(\tau(U_{(-1,-1)}(g))))=U_{(-1,-1)}(g)$ this gives
\begin{align}
&=\Ad{v^\dagger b_g^R v}\circ\pi_0\circ\alpha_0\circ\Theta\circ\Ad{U_{(-1,-1)}(g)}\circ\tau^{-1}\circ\eta_g^R\circ\tau\circ\beta_g^{R,L_{-1}}\circ\nu^{-1}\circ(\eta_g^R)^{-1}\circ\nu\\
\nonumber
&=\Ad{v^\dagger b_g^R vh_g}\circ\pi_0\circ\alpha_0\circ\Theta\circ\tau^{-1}\circ\eta_g^R\circ\tau\circ\beta_g^{R,L_{-1}}\circ\nu^{-1}\circ(\eta_g^R)^{-1}\circ\nu.
\end{align}
Now using again that $\tau\circ\beta_g^{R,L_{-1}}=\beta_{g}^{RU}\circ\tau\circ(\beta_g^{RU})^{-1}$ we get:
\begin{align}
&=\Ad{v^\dagger b_g^R vh_g}\circ\pi_0\circ\alpha_0\circ\Theta\circ\tau^{-1}\circ\eta_g^R\circ\beta_{g}^{RU}\circ\tau\circ(\beta_g^{RU})^{-1}\circ\nu^{-1}\circ(\eta_g^R)^{-1}\circ\nu\\
\nonumber
&=\Ad{v^\dagger b_g^R vh_gK_g^R}\circ\pi_0\circ\alpha_0\circ\Theta\circ\eta_g^R\circ\nu^{-1}\circ(\eta_g^R)^{-1}\circ\nu.
\end{align}
After again using \eqref{eq:automorphismBelongingTo_b} we obtain:
\begin{align}
=\Ad{v^\dagger b_g^R vh_gK_g^R(b_g^R)^\dagger}\circ\pi_0\circ\alpha_0\circ\Theta.
\end{align}
By the irreducibility of $\pi_0$, this implies that there indeed exists such an $\alpha$.
\end{proof}
We have that $h_g\in\IAC_L(\theta,\alpha_0,\Theta)$. On top of that, we also have that
\begin{lemma}\label{lem:W_g_And_h_g_Commute}
For all $g,h\in G$ we have that
\begin{align}
[h_g,W_h]&=0&[h_g,b_h^L]&=0.
\end{align}
\end{lemma}
\begin{proof}
We have that (see figure \ref{fig:SetupForTwoTranslationsNearProof})
\begin{align}
\Ad{W_h}(h_g)&=\pi_0\circ\alpha_0\circ\Theta\circ\eta_h\circ\beta_h^U(U_{(-1,-1)}(g))=\pi_0\circ\alpha_0\circ\Theta(U_{(-1,-1)}(g))=h_g
\end{align}
concluding the proof of the first item. The second proof is analogous.
\end{proof}
Finally, before we can show that the $\alpha$ is a $U(1)$ representation we need to prove an analog of the equation in the 2-cochain lemma \ref{lem:Definition2Cochain}:
\begin{lemma}\label{lem:translating_u_R_To_The_Right_identity}
The equality
\begin{equation}
\Ad{b_g^R W_g b_h^R W_h W_{gh}^\dagger (b_{gh}^R)^\dagger W_{gh}W_h^\dagger W_g^\dagger u_R(g,h)}\circ\pi_0=\Ad{w^\dagger u_R(g,h) w}\circ\pi_0
\end{equation}
holds.
\end{lemma}
\begin{proof}
The proof is analogous to the proof of \ref{lem:Definition2Cochain}. We now show that
\begin{equation}
\Ad{b_g W_g b_h W_h W_{gh}^\dagger (b_{gh})^\dagger W_{gh}W_h^\dagger W_g^\dagger u_L(g,h)\otimes u_R(g,h)}\circ\pi_0=\Ad{w^\dagger u_R(g,h)\otimes u_R(g,h) w}\circ\pi_0
\end{equation}
holds. This part is completely the same. Afterwards we have to prove that: $b_g W_g b_h W_h W_{gh}^\dagger (b_{gh})^\dagger W_{gh}W_h^\dagger W_g^\dagger$, is split. This is a straightforward calculation.
\end{proof}
We now need to prove the analogue of \ref{lem:3cochainIsInvariant}.
\begin{lemma}\label{lem:2cochainIsInvariant}
The two-cochain as defined through
\begin{equation}\label{eq:Definition2Cochain2TranslationSectionAppendix}
K_g^RW_gK_h^RW_hW_{gh}^\dagger(K_{gh}^R)^\dagger W_{gh}W_{h}^\dagger W_g^\dagger u_R(g,h)=C(g,h)v^\dagger u_R(g,h)v.
\end{equation}
is invariant under the substitution
\begin{align}
K_g^R&\mapsto v^\dagger b_g^R v h_g K_g^R (b_g^R)^\dagger&W_g&\mapsto w^\dagger W_g w&u_R(g,h)&\mapsto w^\dagger u_R(g,h)w.
\end{align}
\end{lemma}
\begin{proof}
To show this, notice that we have by construction and by lemma \ref{lem:translating_u_R_To_The_Right_identity} that
\begin{align}
\Ad{b_g W_g}\circ\pi_0&=\Ad{w^\dagger W_g w}\circ\pi_0\\
\Ad{b_g^R W_g b_h^R W_h W_{gh}^\dagger (b_{gh}^R)^\dagger W_{gh}W_h^\dagger W_g^\dagger u_R(g,h)}\circ\pi_0&=\Ad{w^\dagger u_R(g,h) w}\circ\pi_0.
\end{align}
This shows that there exists a $\beta:G\rightarrow U(1)$ and a $\gamma:G\times G\rightarrow U(1)$ such that
\begin{align}
w^\dagger W_g w&=\beta(g)b_g^Lb_g^RW_g&w^\dagger u_R(g,h) w&=\gamma(g,h)b_g^R W_g b_h^R W_h W_{gh}^\dagger (b_{gh}^R)^\dagger W_{gh}W_h^\dagger W_g^\dagger u_R(g,h).
\end{align}
Since the equation is invariant under the substitution with these two phases all that is left to do is to show that equation \eqref{eq:Definition2Cochain2TranslationSectionAppendix} is invariant under the substitution:
\begin{align}
K_g^R&\mapsto v^\dagger b_g^R v h_g K_g^R (b_g^R)^\dagger=v^\dagger b_g^R v K_g^R (b_g^R)^\dagger h_g&W_g&\mapsto b_g^Lb_g^RW_g
\end{align}
\begin{equation}
u_R(g,h)\mapsto b_g^R W_g b_h^R W_h W_{gh}^\dagger (b_{gh}^R)^\dagger W_{gh}W_h^\dagger W_g^\dagger u_R(g,h).
\end{equation}
To show this first notice that by using the fact that $h_g\in\IAC_R(\theta,\alpha_0,\Theta)'$ and lemma \ref{lem:W_g_And_h_g_Commute} we get that
\begin{align}
&K_g^R W_g K_h^R W_ hW_{gh}^\dagger(K_{gh}^R)^\dagger\\
\nonumber
&\mapsto v^\dagger b_g^R v \underline{h_g} K_g^R (b_g^R)^\dagger b_g^Lb_g^RW_g v^\dagger b_h^R v \underline{h_h} K_h^R (b_h^R)^\dagger b_h^Lb_h^RW_h W_{gh}^\dagger (b_{gh}^Lb_{gh}^R)^\dagger (v^\dagger b_{gh}^R v \underline{h_{gh}} K_{gh}^R (b_{gh}^R)^\dagger)^\dagger\\
\nonumber
&=\underline{h_gh_hh_{gh}^\dagger} v^\dagger b_g^R v K_g^R (b_g^R)^\dagger b_g^Lb_g^RW_g v^\dagger b_h^R v K_h^R (b_h^R)^\dagger b_h^Lb_h^RW_h W_{gh}^\dagger (b_{gh}^Lb_{gh}^R)^\dagger (v^\dagger b_{gh}^R v K_{gh}^R (b_{gh}^R)^\dagger)^\dagger
\end{align}
(all the $h-$operators can be put in front). Since $h_g$ is an honest representation we get that the $h-$operators cancel out. This leaves us with checking that equation \eqref{eq:Definition2Cochain2TranslationSectionAppendix} is invariant under
\begin{align}
K_g^R&\mapsto v^\dagger b_g^R v K_g^R (b_g^R)^\dagger&W_g&\mapsto b_g^Lb_g^RW_g
\end{align}
\begin{equation*}
u_R(g,h)\mapsto b_g^R W_g b_h^R W_h W_{gh}^\dagger (b_{gh}^R)^\dagger W_{gh}W_h^\dagger W_g^\dagger u_R(g,h).
\end{equation*}
Using the fact that
\begin{align}
(b_{gh}^R)^\dagger W_{gh}W_h^\dagger W_g^\dagger u_R(g,h)&=(b_{gh}^R)^\dagger u_L(g,h)^\dagger=u_L(g,h)^\dagger(b_{gh}^R)^\dagger=W_{gh}W_h^\dagger W_g^\dagger u_R(g,h) (b_{gh}^R)^\dagger
\end{align}
we see that we can prove that our equation is invariant under the substitution using lemma \ref{lem:TransformationUnderDelta}. This concludes the proof.
\end{proof}
Using this we can show that:
\begin{lemma}
The $\alpha$ defined previously is a $U(1)$-representation.
\end{lemma}
\begin{proof}
Take the definition of the 2-cochain (lemma \ref{lem:Definition2Cochain}). This equation is invariant under the substitution
\begin{align}
K_g^R&\mapsto w^\dagger K_g^R w&W_g&\mapsto w^\dagger W_g w&u_R(g,h)&\mapsto w^\dagger u_R(g,h)w.
\end{align}
If we now also show that it is invariant under the substitution
\begin{align}
K_g^R&\mapsto v^\dagger b_g^R v h_g K_g^R (b_g^R)^\dagger&W_g&\mapsto w^\dagger W_g w&u_R(g,h)&\mapsto w^\dagger u_R(g,h)w
\end{align}
then we get using the definition of $\alpha$ that
\begin{equation}
\stkout{C(g,h)}=\stkout{C(g,h)}\frac{\alpha(g)\alpha(h)}{\alpha(gh)}
\end{equation}
which would conclude the proof. This invariance is proven in lemma \ref{lem:2cochainIsInvariant}.
\end{proof}
\begin{definition}\label{def:DefinitionOfTheH1ValuedIndex}
Let $\alpha$ be the $U(1)$-representation defined in lemma \ref{lem:DefinitionAlpha}. Take $\phi\in\hom(G,\TT)$ such that $\alpha(g)=\exp(i\phi(g))$. We define the 2 translation index as
\begin{equation}
\textrm{Index}_{2\:\text{trans}}^{\AA,U}(\theta,\tilde{\beta}_g,\eta_g,\alpha_0,\Theta,\omega,\omega_0)\defeq \phi\in H^1(G,\TT)
\end{equation}
and (as advertised) it is only a function of the automorphisms (and the product state) not of the choice of the GNS triple of $\omega_0$ or the choice of phases in $W_g,u_L(g,h),u_R(g,h),v,w,K^L_g,K^R_g,b^L_g$ and $b^R_g$.\footnote{It is however explicitly dependent on the on-site group action $U$, and not only $\Ad{U}$.}
\end{definition}
\begin{proof}
The construction is invariant under the choice of GNS triple since this simply amounts to an adjoint action by some unitary on every operator. The proof that it is independent of the choice of phases is just as trivial.
\end{proof}
One can also define this index starting from operators acting on the left. As the following lemma shows this gives us the opposite index (the complex conjugate of the $U(1)$-representation):
\begin{lemma}
Define $\tilde{\alpha}(g)$ such that
\begin{equation}\label{eq:DefinitionOfTheH_1IndexAlternative}
v^\dagger b_g^L v h_g^\dagger K_g^L (b_g^L)^\dagger=\tilde{\alpha}(g)w^\dagger K_g^L w
\end{equation}
then $\alpha(g)\tilde{\alpha}(g)=1$.
\end{lemma}
\begin{proof}
By multiplying the left hand side of equation \eqref{eq:DefinitionOfTheH_1IndexAlternative} with the left hand side of equation \eqref{eq:DefinitionOfTheH_1Index} we obtain
\begin{equation}
v^\dagger b_g v K_g b_g^\dagger=v^\dagger b_g v v^\dagger W_g v W_g^\dagger b_g^\dagger=w^\dagger v^\dagger W_g v W_g^\dagger w=w^\dagger K_g w
\end{equation}
whereas by multiplying the right-hand sides of equations \eqref{eq:DefinitionOfTheH_1IndexAlternative} and \eqref{eq:DefinitionOfTheH_1Index} we would obtain $\alpha(g)\tilde{\alpha}(g)w^\dagger K_g w$. These two results can only be consistent if the lemma holds.
\end{proof}
\section{The indices are well-defined}\label{sec:IndexIsInvariantUnderChoices}
In this section, we will show that the index from definition \ref{def:DefinitionOfTheH2ValuedIndex} and the index from definition \ref{def:DefinitionOfTheH1ValuedIndex} are only dependent on $\omega$ and not on the choices of our automorphisms nor on $\omega_0$. On this last item, we remark:
\begin{remark}\label{rem:NontrivialProductState}
A product state can have a non-trivial $H^1(G,\TT)$ index and the index is not defined relative to $\omega_0$ so in particular
\begin{equation}
\textrm{Index}_{2\:\text{trans}}^{\AA,U}(\theta,\beta_g^U,\textrm{Id},\textrm{Id},\textrm{Id},\omega_0,\omega_0)
\end{equation}
can still be non-trivial. In fact in this case we get $\alpha(g)=\omega_0(U_{(-1,-1)}(g))$. To show this, notice that we can take $b_g=\id_{\HH}$ and we can choose $K_g^R$ so that it leaves the cyclic vector of $\omega_0$, $\Omega_0$ invariant. Applying the definition of the index on this cyclic vector then gives us $h_g\Omega_0=\alpha(g)\Omega_0$. This obviously implies that $\bra{\Omega_0}\ket{h_g\Omega_0}=\alpha(g)\bra{\Omega_0}\ket{\Omega_0}$ giving us indeed the advertised equation.
\end{remark}
We now show independence on $\alpha$ and the choice of its decomposition.
\begin{lemma}
Take $\omega_{01},\omega_{02}\in\PP(\AA)$ product states and let $\alpha_1,\alpha_2\in\Aut{\AA}$ be such that $\omega_{01}\circ\alpha_1=\omega_{02}\circ\alpha_2=\omega$. Let $V_{11},V_{12}\in\UU(\AA)$, $\alpha_{L/R,1},\alpha_{L/R,2}\in\Aut{\AA_{L/R}}$ and $\Theta_1,\Theta_2\in \Aut{\AA_{W(C_\theta)^c}}$ be such that $\alpha_1=\Ad{V_{11}}\circ\alpha_{01}\circ\Theta_1$ and $\alpha_2=\Ad{V_{12}}\circ\alpha_{02}\circ \Theta_2$ with $\alpha_{0,i}=\alpha_{L,i}\otimes\alpha_{R,i}$, then
\begin{equation}
\textrm{Index}^{\AA,U}(\theta,\tilde{\beta}_g,\eta_g,\alpha_{0,1},\Theta_1,\omega,\omega_{01})=\textrm{Index}^{\AA,U}(\theta,\tilde{\beta}_g,\eta_g,\alpha_{0,2},\Theta_2,\omega,\omega_{02}).
\end{equation}
Additionally, when $\omega$ satisfies assumption \ref{assumption:2Translations},
\begin{equation}
\textrm{Index}^{\AA,U}_{\text{2 trans}}(\theta,\tilde{\beta}_g,\eta_g,\alpha_{0,1},\Theta_1,\omega,\omega_{01})=\textrm{Index}^{\AA,U}_{\text{2 trans}}(\theta,\tilde{\beta}_g,\eta_g,\alpha_{0,2},\Theta_2,\omega,\omega_{02}).
\end{equation}
\end{lemma}
\begin{proof}
We will first prove the result in the case that $\omega_0=\omega_{01}=\omega_{02}$ and then generalize this result. Since $\omega_0\circ\alpha_2\circ\alpha_1^{-1}=\omega_0$ there exists a $\tilde{x}\in\UU(\HH_0)$ such that $\pi_0\circ\alpha_2\circ\alpha_1^{-1}=\Ad{\tilde{x}}\circ\pi_0$. Now define $x\in\UU(\HH_0)$ to be $x\defeq \pi_0(V_{12}^\dagger)\tilde{x} \pi_0(V_{11})$ then
\begin{equation}
\pi_0\circ\alpha_{02}\circ\Theta_2=\Ad{x}\circ\pi_0\circ\alpha_{01}\circ\Theta_1.
\end{equation}
Now take $W_{g,1},u_{R,1}(g,h), v$ and $K^R_{g,1}$ to be the operators belonging to the first choice (with arbitrary phases). When, $\omega$ satisfies assumption \ref{assumption:2Translations}, also take $b^R_{g,1}$ and $w$, the additional operators belonging to the first choice.
We have (see \cite{ogata2021h3gmathbb} lemma 2.11)
\begin{align}
\Ad{xW_{g,1}x^\dagger}\circ\pi_0&=\pi_0\circ \alpha_{02}\circ\Theta_2\circ\eta_g\circ\beta_g^U\circ\Theta_2^{-1}\circ\alpha_{02}^{-1},\\
\nonumber
\Ad{xu_{R,1}(g,h)x^\dagger}\circ\pi_0&=\pi_0\circ \alpha_{02}\circ\eta_g^R\circ\beta_g^{RU}\circ\eta_h^R\circ\beta_{h}^{RU}\circ(\beta_{gh}^{RU})^{-1}\circ(\eta_{gh}^R)^{-1}\circ\alpha_{02}^{-1}.
\end{align}
Through similar arguments we get
\begin{align}
\Ad{xvx^\dagger}\circ\pi_0&=\pi_0\circ\alpha_{02}\circ\Theta_2\circ\tau\circ\Theta_2^{-1}\circ\alpha_{02}^{-1}\\
\nonumber
\Ad{xK^R_{g,1}x^\dagger}\circ\pi_0&=\pi_0\circ \alpha_{02}\circ\tau^{-1}\circ\eta_g^R\circ\beta_g^{RU}\circ\tau\circ(\beta_g^{RU})^{-1}\circ(\eta^R_g)^{-1}\circ\alpha_{02}^{-1}