Hearing the signals of dark sectors with gravitational wave detectors

TL;DR

The paper investigates how gravitational-wave detectors can probe dark sectors via two distinct signatures: stochastic gravitational waves from first-order phase transitions in a high-scale dark sector, and transient signals from domain walls passing through detectors. It models a classically scale-invariant Coleman–Weinberg dark sector with a Higgs portal, computes the finite-temperature effective potential, and analyzes bubble nucleation using thin-wall and triangle approximations to extract key transition parameters such as $\beta/H_*$ and $\alpha$, which shape the predicted GW spectrum from bubble collisions, sound waves, and turbulence. It also details domain-wall interactions with photons, showing that domain-wall crossings can produce observable, non-GW transients with distinctive temporal profiles and multi-detector timing signatures. Together, the results map out regimes where current and future GW experiments—ranging from aLIGO to BBO/DECIGO—can test high-scale dark physics, and they emphasize the complementary potential of domain-wall searches and phase-transition signals in revealing weakly coupled hidden sectors.

Abstract

Motivated by aLIGO's recent discovery of gravitational waves we discuss signatures of new physics that could be seen at ground and space-based interferometers. We show that a first order phase transition in a dark sector would lead to a detectable gravitational wave signal at future experiments, if the phase transition has occurred at temperatures few orders of magnitude higher than the electroweak scale. The source of gravitational waves in this case is associated with the dynamics of expanding and colliding bubbles in the early universe. At the same time we point out that topological defects, such as dark sector domain walls, may generate a detectable signal already at aLIGO. Both -- bubble and domain wall -- scenarios are sourced by semi-classical configurations of a dark new physics sector. In the first case the gravitational wave signal originates from bubble wall collisions and subsequent turbulence in hot plasma in the early universe, while the second case corresponds to domain walls passing through the interferometer at present and is not related to gravitational waves. We find that aLIGO at its current sensitivity can detect smoking-gun signatures from domain wall interactions, while future proposed experiments including the fifth phase of aLIGO at design sensitivity can probe dark sector phase transitions.

Figures (10)

• Figure 1: The zero-temperature effective potential $V$ of the CW theory Eq. \ref{['V1RR']} in the units of $\frac{3}{64 \pi ^2} \, g_{ \mathrm{D}}^4$.
• Figure 2: Thermal effective potential $\hat{V}(\gamma,\Theta)$ of the dark sector in Eq. \ref{['eq:VT1']} as a function of $\gamma=\phi/w$ plotted for different temperatures $\Theta=$ 0.40, 0.35, 0.31, 0.25, 0.20 and 0 (from top to bottom). We have shifted $\hat{V}(\gamma,\Theta)$ by a constant so that the effective potential at the origin is zero for all values of $\Theta$.
• Figure 3: Thermal effective potential $\hat{V}(\gamma,\Theta)$ as in Fig \ref{['fig:VT1']} now zooming at the values around the critical temperature, $\Theta=$ 0.315, 0.312, 0.309 (from top to bottom).
• Figure 4: $\epsilon$ as a function of the nucleation temperature $T_*$ for $T_* \le T_c$.
• Figure 5: Numerical values for $\beta/H_{*}$ (left) and $\alpha$ (right) for values $g_{ \mathrm{D}}\geq 0.1$ in the triangle approximation (blue lines). In the right panel the green line indicates the value of $\alpha_{\infty}$ according to Eq. \ref{['alphastar']} and the golden line indicates $\alpha=1$.