Gravitational waves in models with multicritical-point principle

TL;DR

This paper explores a model extending the Standard Model with two scalar fields, applying the multicritical-point principle to explain hierarchy, dark matter, and predict gravitational waves detectable by future space-based observatories.

Contribution

It introduces a specific critical point scenario within the MPP framework that addresses dark matter, phase transitions, and gravitational wave predictions.

Findings

Identifies parameter regions satisfying dark matter relic abundance and experimental bounds.

Predicts a first-order phase transition at TeV scale in the early universe.

Forecasts gravitational waves with specific amplitude and frequency detectable by future missions.

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 $\phi$ and $S$, and a dimensional transmutation occurs by the vacuum expectation value of $\phi$. In this paper, we focus on the critical points that possess a $\mathbb Z_2$ symmetry $S\rightarrow -S$ 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 $\phi$ 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 ${\cal O}(10^{-12})$ at a frequency of $10^{-2}$-$10^{-1}$ Hz, which can be tested with future space-based instruments such as DECIGO and BBO.