Gravitational waves from domain wall collapses and dark matter in the SM with a complex scalar field

Abstract

We study a domain wall induced by spontaneously broken Z2 symmetry and its gravitational wave signature in the standard model with a complex scalar in connection with dark matter physics. In a minimal setup, a linear term of the singlet field is added to the scalar potential as an explicit Z2 breaking term to make the domain wall unstable. We obtain its minimal size from cosmological constraints and show that the parameter space that can be probed by current and future pulsar time array experiments requires the vacuum expectation value of the singlet field to be greater than O(10–100)  TeV, along with a singletlike Higgs mass of O(1–100)  TeV. However, such a region is severely restricted by the dark matter relic density, which places an upper bound on the singlet vacuum expectation value at approximately 200 TeV, and limits the dark matter mass to about half of the singletlike Higgs boson mass. Published by the American Physical Society 2024