Lepton parity dark matter and naturally unstable domain walls

Abstract

We propose a simple and predictive setup that connects neutrino masses, dark matter (DM), and gravitational waves. A minimal lepton parity DM scenario is considered where the residual symmetry $(-1{)}^L$ from the type I seesaw acts as the dark parity $D=(-1{)}^{L+2j}$, ensuring DM stability without imposing any new symmetry. A singlet Majorana fermion $S$ with even lepton parity serves as the DM candidate, interacting via a real scalar $\sigma$ which is also even lepton parity. The scalar potential possesses an accidental ${\mathcal{Z}}_2$ symmetry, whose spontaneous breaking gives rise to unstable domain walls (DW) in the presence of explicit ${\mathcal{Z}}_2$ breaking terms allowed by the lepton parity. The subsequent DW annihilation generates a stochastic gravitational wave (GW) background potentially observable at different GW experiments.

v2: 5+5 pages, 2+4 captioned figures, 1+2 tables, version accepted for publication in Phys. Rev. D

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• The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
• Exploring the Sensitivity of Next Generation Gravitational Wave Detectors
• Derivation of Dark Matter Parity from Lepton Parity
• Thermal leptogenesis, dark matter, and gravitational waves from an extended canonical seesaw scenario

Cited by in corpus (1)

• Cosmological Probes of Lepton Parity Freeze-in Dark Matter: $\Delta N_{\mathrm{eff}}$ & Gravitational Waves