Gravitational waves in models with multicritical-point principle

Abstract

The multicritical-point principle (MPP) provides a natural explanation of the large hierarchy between the Planck and electroweak scales. We consider a scenario in which MPP is applied to the Standard Model extended by two real singlet scalar fields $\varphi$ and $S$, and a dimensional transmutation occurs by the vacuum expectation value of $\varphi$. In this paper, we focus on the critical points that possess a ${\mathbb{Z}}_2$ symmetry $S\to -S$ and all the other fields are left invariant. Then $S$ becomes a natural dark matter (DM) candidate. Further, we concentrate on the critical points where $\varphi$ does not possess further ${\mathbb{Z}}_2$ symmetry so that there is no cosmological domain-wall problem. Among such critical points, we focus on maximally critical one called CP-1234 that fix all the superrenormalizable parameters. We show that there remains a parameter region that satisfies the DM relic abundance, DM direct-detection bound and the current LHC constraints. In this region, we find a first-order phase transition in the early universe around the TeV-scale temperature. The resultant gravitational waves are predicted with a peak amplitude of $\mathcal{O}(10^{-12})$ at a frequency of $10^{-2}$-$10^{-1}$ Hz, which can be tested with future space-based instruments such as DECIGO and BBO.

Comments: 22 pages, 6 figures