Gravitational waves as a probe of extended scalar sectors with the first order electroweak phase transition

TL;DR

This work addresses whether gravitational waves can serve as a probe of electroweak baryogenesis in extended scalar sectors. It analyzes an $O(N)$-symmetric scalar-singlet extension without relying on high-temperature expansion and computes the finite-temperature effective potential to determine regions where the transition is strongly first-order, via $\varphi_c/T_c>1$. The authors then predict the gravitational-wave spectra from bubble collisions and plasma turbulence, showing that the signal strength grows with $N$ and can fall within the sensitivity of future detectors such as DECIGO and BBO, with the amplitude closely tied to the transition strength. The results imply that future gravitational-wave observations could disclose the presence and properties of extended scalar sectors relevant for EWBG, complementing collider probes of the Higgs sector.

Abstract

We discuss spectra of gravitational waves which are originated by the strongly first order phase transition at the electroweak symmetry breaking, which is required for a successful scenario of electroweak baryogenesis. Such spectra are numerically evaluated without high temperature expansion in a set of extended scalar sectors with additional N isospin-singlet fields as a concrete example of renormalizable theories. We find that the produced gravitational waves can be significant, so that they are detectable at future gravitational wave interferometers such as DECIGO and BBO. Furthermore, since the spectra strongly depend on N and the mass of the singlet fields, our results indicate that future detailed observation of gravitational waves can be in general a useful probe of extended scalar sectors with the first order phase transition.

Figures (2)

• Figure 1: The allowed region which satisfies both $\varphi_c/T_c> 1$ and $T_c>0$, where EWBG can be viable with the strongly 1stOPT on the plane of $\sqrt{\mu_S^2}$ and $m_S$ in the left figure and on the plane of $N$ and $m_S$ in the right figure. We set $N=12$ for the left figure, and $\mu_S^2=0$ for the right figure. Contours for the deviation in the $hhh$ coupling from the SM prediction are also shown in both figures. Bounds from vacuum stability and perturbative unitarity are also shown for $\lambda_S^{} =0$kkm_full.
• Figure 2: (Left) Spectra of GWs in the $O(N)$ singlet model with expected experimental sensitivities at the future GW interferometers, eLISA, DECIGO/BBO and Ultimate-DECIGO (U-DECIGO) are shown for $\sqrt{\mu_S^2} =0$. The bound from non-observation of the energy density of extra radiation is indicated by $\Delta N_\nu \gtrsim 1$planckAgashe:2014kda, and the estimated foreground noise from the white dwarf binaries is also shown. (Right) Predictions of the model on the $(\alpha, \tilde{\beta})$ plane with various $N$ and $m_S^{}$ assuming $\sqrt{\mu_S^2} =0$ and $T_t = 100$ GeV are shown with regions of expected experimental sensitivity at the future GW interferometers.