Twin-peaked gravitational wave signal from a dark sector phase transition

Abstract

We compute the gravitational wave spectrum from a dark sector phase transition driven by spontaneous $\ZDW$ breaking. If the transition is second-order, the only source of gravitational waves is the annihilation of domain walls (biased by quantum gravity). However, if the transition is first-order, this yields a twin-peaked signal from both the transition itself and the biased domain wall annihilation. Both scenarios originate when a scalar singlet odd under the $\ZDW$ obtains a non-zero vacuum expectation value. An additional $\ZDM$ odd scalar doublet strengthens the transition and produces fermionic dark matter via freeze-in, matching observed dark matter relic density.

Figures (6)

• Figure 1: Temperature dependence of the effective potential $V_{\rm eff}(S,T)$ for SOPT. The potential profiles are shown for $\lambda_s = 0.01$, $\lambda_{\eta S} = 0.2$, and $v_s = 10^6~\mathrm{GeV}$.
• Figure 2: Temperature evolution of the effective scalar potential showing a FOPT. The potential profiles are shown for $\lambda_s = 0.01$, $\lambda_{\eta S} = 1.0$, and $v_s = 10^6~\mathrm{GeV}$.
• Figure 3: Parameter space in the $\lambda_s$--$\lambda_{\eta S}$ plane for $v_s = 10^6~\mathrm{GeV}$ and $\mu_\eta=10^{-2}v_s$. The dashed black line corresponds to the contour $v_c/T_c = 1$, indicating the boundary for a strong FOPT.
• Figure 4: The gravitational wave spectrum produced from the annihilation of domain walls corresponds to the benchmark points listed in table \ref{['BP']}.
• Figure 5: The combined gravitational wave spectrum arising from the FOPT and the annihilation of domain walls corresponds to the benchmark points listed in table \ref{['BP']} and \ref{['BP_gw']}.