95 GeV Higgs boson and nano-Hertz gravitational waves from domain walls in the N2HDM

TL;DR

This paper investigates the 95 GeV Higgs-like excesses and nano-Hertz gravitational waves from domain walls in the N2HDM, proposing scenarios that explain experimental signals and predict detectable gravitational wave signatures.

Contribution

It introduces two scenarios within the N2HDM framework that simultaneously explain Higgs excesses and predict gravitational wave signals from domain walls.

Findings

Scenario A explains Higgs excesses within 1σ.

Gravitational wave amplitude can reach 2×10⁻¹² at 10⁻⁹ Hz for v_s=100 TeV.

Scenario B marginally explains Higgs excesses but predicts higher gravitational wave amplitude.

Abstract

We explore the diphoton and $b\bar{b}$ excesses at 95.4 GeV, as well as nano-Hertz gravitational waves originating from domain walls, within the framework of the next-to-two-Higgs-doublet model (N2HDM), which extends the two-Higgs-doublet model by introducing a real singlet scalar subject to a discrete $Z_2$ symmetry. The $Z_2$ symmetry is spontaneously broken by the non-zero vacuum expectation value of the singlet scalar, $v_s$, which leads to the formation of domain walls. We discuss two different scenarios: in scenario A, the 95.4 GeV Higgs boson predominantly originates from the singlet field, while in scenario B, it arises mainly from the CP-even components of the Higgs doublets. Taking into account relevant theoretical and experimental constraints, we find that scenario A can fully account for both the diphoton and $b\bar{b}$ excesses at 95.4 GeV within the $1\sigma$ range. Moreover, the peak amplitude of the gravitational wave spectrum at a peak frequency of $10^{-9}$ Hz can reach $2 \times 10^{-12}$ for $v_s = 100$ TeV. Scenario B only marginally accounts for the diphoton and $b\bar{b}$ excesses at the $1\sigma$ level, but the peak amplitude of the gravitational wave spectrum at the peak frequency of $10^{-9}$ Hz can reach $6\times 10^{-8}$ for $v_s=100$ TeV. The nano-Hertz gravitational wave signals predicted in both scenarios can be tested by the current and future pulsar timing array projects.