We show how weak symmetry protected topological (SPT) phases on systems with a boundary are not in 1-to-1 correspondence with weak SPT phases on fully periodic systems, breaking the standard anomaly inflow interpretation of SPT phases. We further discuss the implications for the crystalline equivalence principle (CEP).
@article{arxiv.2507.17179,
title = {Weak in the boundary: How weak SPT phases spoil anomaly matching},
author = {Daniel Sheinbaum and Omar Antolín Camarena},
journal= {arXiv preprint arXiv:2507.17179},
year = {2025}
}