Discrete symmetries in dimer diagrams
We apply dimer diagram techniques to uncover discrete global symmetries in the fields theories on D3-branes at singularities given by general orbifolds of general toric Calabi-Yau threefold singularities. The discrete symmetries are discrete Heisenberg groups, with two Z generators A, B with commutation AB = CBA, with C a central element. This fully generalizes earlier observations in particular orbifolds of C, the conifold and Y. The solution for any orbifold of a given parent theory follows from a universal structure in the infinite dimer in R giving the covering space of the unit cell of the parent theory before orbifolding. The generator A is realized as a shift in the dimer diagram, associated to the orbifold quantum symmetry; the action of B is determined by equations describing a 1-form in the dimer graph in the unit cell of the parent theory with twisted boundary conditions; finally, C is an element of the (mesonic and baryonic) non-anomalous U(1) symmetries, determined by geometric identities involving the elements of the dimer graph of the parent theory. These discrete global symmetries of the quiver gauge theories are holographically dual to discrete gauge symmetries from torsion cycles in the horizon, as we also briefly discuss. Our findings allow to easily construct the discrete symmetries for infinite classes of orbifolds. We provide explicit examples by constructing the discrete symmetries for the infinite classes of general orbifolds of C, conifold, and complex cones over the toric del Pezzo surfaces, dP, dP and dP. ; This work is supported through the grants SEV-2016-0597, FPA2015-65480-P and PGC2018- 095976-B-C21 from MCIU/AEI/FEDER, UE. AM received funding from "la Caixa" Foundation (ID 100010434) with fellowship code LCF/BQ/IN18/11660045 and from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 713673.
