Speaker
Description
Discrete flavour symmetries are widely used to address flavour puzzles in quark and lepton sectors. A key cosmological consequence for spontaneous breaking of these symmetries are the formation of domain walls (DWs), 2D topological defects at the cosmic scale. DWs, if they are generated in the radiation era, should collapse before BBN in order to avoid overclosing the Universe. The collapsing DWs radiate gravitational waves (GWs), which has been considered as one of the main sources of GWs with particle origins. This framework has gained renewed traction as the resulting GW spectrum can gain excellent agreement with the 2023 Pulsar Timing Array (PTA) data. While literature predominantly focuses on $Z_2$ symmetry breaking, this presentation explores DWs from larger Abelian and non-Abelian discrete symmetries, both highly motivated by flavour models. After reviewing the standard $Z_2$ DW case, we characterize DWs from general $Z_N$ breaking. We then analyze non-Abelian DWs using octahedral ($S_4$) and tetrahedral ($A_4$) symmetries as benchmarks. CP-violating DWs arise when complex structures are included. We further discuss unique properties of SUSY and modular DWs with conventional non-SUSY scenarios.