1pm - 2pm: Chiral Symmetry Breaking, Gravitational Waves and the Origin of the Dark Eta Prime Mass in Confining Dark Sectors

Dark confining sectors are phenomenologically rich. For instance a confining phase transition can be used to trigger baryogenesis, and some heavy axion models identify the dark \eta′ particle as an axion candidate. By modelling the dark confining phase transition with spontaneous symmetry breaking of chiral symmetry, previous studies have found that a Gravitational Wave (GW) signal could be visible at future experiments. The mesonic potential is often modeled with a Linear Sigma Model, including an explicit U(1)_A breaking term to generate the \eta’ mass.

The \eta′ meson gains its mass directly from the U(1)_A anomaly; commonly this is argued to be generated by instanton effects. However, following instead the recent argument that results in QCD-like theories can be obtained from exact results in Anomaly Mediated Supersymmetry Breaking, the \eta′ mass cannot be generated by instanton effects. Interestingly, the modified explicit U(1)_A breaking term proposed following this argument also explicitly breaks chiral symmetry. With the EFT we can only describe a secondary phase transition between non-symmetric vacua. We will discuss such a phase transition in this talk, including possible GW spectra were this phase transition first-order.