Detecting the relic gravitational wave from the electroweak phase transition at SKA

TL;DR

The paper addresses the prospect of directly detecting stochastic gravitational waves from a first-order electroweak phase transition using SKA, focusing on the $f\in[10^{-9},10^{-4}]$ Hz band. It develops a model-independent framework based on the envelope approximation, reducing the problem to two fundamental parameters, $\alpha$ and $\tilde{\beta}$, and provides analytic expressions for peak frequencies and GW amplitudes from bubble collisions and turbulence, including possible vacuum-energy effects. By comparing these predictions to sensitivities of SKA, eLISA, and DECIGO, the authors show that SKA can probe MSSM-motivated regions with small $\tilde{\beta}$ and discriminate between particle-physics models through GW observations. The work highlights the potential of pulsar timing arrays to probe electroweak-scale Higgs-sector physics and test beyond-Standard-Model scenarios at cosmological frequencies.

Abstract

We discuss possibilities to observe stochastic gravitational wave backgrounds produced by the electroweak phase transition in the early universe. Once the first-order phase transition occurs, which is still predicted in a lot of theories beyond the standard model, collisions of nucleated vacuum bubbles and induced turbulent motions can become significant sources of the gravitational waves. Detections of such gravitational wave backgrounds are expected to reveal the Higgs sector physics. In particular, through pulsar timing experiments planned in Square Kilometre Array (SKA) under construction, we will be able to detect the gravitational wave in near future and distinguish particle physics models by comparing the theoretical predictions to the observations.

Figures (7)

• Figure 1: Plot of the condition for completion of the percolation $\Gamma/ H^4 = 1$. The horizontal axis is the cosmic temperature in GeV. Here we took vacuum energy $\Lambda_{\rm{vac}} \equiv \Delta V_{\rm eff}(T=0)=0$.
• Figure 2: Same as Fig. \ref{['fig:percolation_novacuum']}, but changing the vacuum energy. From right to left, we took $\Lambda_{\rm{vac}} \equiv \Delta V_{\rm eff}(T=0)=$$(0)^4, (250)^4, (500)^4$, and $(1000)^4 \text{GeV}^4$.
• Figure 3: Experimental sensitivities of eLISA, DECIGO, SKA, Advanced LIGO/VIRGO, KAGRA, and ET. The horizontal line means the upper bound from the CMB observations by PLANCK given in Eq. (\ref{['eq:OmegaDeltaNnu']}). "Pulsar" denotes the upper bound obtained from the existing pulsar timing experiments. The WD-WD line stands for the foreground noise from white dwarf binaries Schneider:2010ks. The detail of each experimental line is given in the text and Refs. Alabidi:2013lyaRegimbau:2012ir
• Figure 4: Signals of the relic gravitational wave background in case of the bubble collision. The band regions mean the peak signals $\tilde{\Omega}h^2$ for $T = 70 \text{GeV}$, and $T = 100 \text{GeV}$ from the left to the right, respectively. The broken power means the corresponding full spectrum whose peak is located at $\Omega h^2=\tilde{\Omega}h^2$. The model parameters are changed to be $\{\alpha,\tilde{\beta}\}=\{0.1,0.1\},\{0.1,10^4\},\{10,0.1\},\{10,10^4\}$. We assumed $g_* = 106.75$.
• Figure 5: Same as Fig. \ref{['fig:bubble_collision']}, but for the case of the turbulence.