Type-I two-Higgs-doublet model and gravitational waves from domain walls bounded by strings

TL;DR

This paper explores how a specific particle physics model predicts a unique gravitational wave signature from topological defects, which could be detected by future interferometers, linking cosmology and particle physics.

Contribution

It introduces a novel gravitational wave production mechanism from domain walls bounded by strings within a type-I two-Higgs-doublet model with a $U(1)_R$ symmetry, connecting it to observable signals.

Findings

Detectable gravitational wave spectrum for $U(1)_R$ breaking scale between $10^{12}$ and $10^{15}$ GeV.

Distinctive $f^{3}$ slope and inflexion in the frequency spectrum.

Potential detection with LISA and Einstein Telescope.

Abstract

The spontaneous breaking of a $U(1)$ symmetry via an intermediate discrete symmetry may yield a hybrid topological defect of \emph{domain walls bounded by cosmic strings}. The decay of this defect network leads to a unique gravitational wave signal spanning many orders in observable frequencies, that can be distinguished from signals generated by other sources. We investigate the production of gravitational waves from this mechanism in the context of the type-I two-Higgs-doublet model extended by a $U(1)_R$ symmetry, that simultaneously accommodates the seesaw mechanism, anomaly cancellation, and eliminates flavour-changing neutral currents. The gravitational wave spectrum produced by the string-bounded-wall network can be detected for $U(1)_R$ breaking scale from $10^{12}$ to $10^{15}$ GeV in forthcoming interferometers including LISA and Einstein Telescope, with a distinctive $f^{3}$ slope and inflexion in the frequency range between microhertz and hertz.