Can a secluded self-interacting dark sector generate detectable gravitational waves?

TL;DR

This paper investigates whether a secluded, self-interacting dark sector can produce detectable gravitational waves, concluding that current cosmological constraints make such signals unlikely to be observed by future detectors.

Contribution

It introduces a model with a spontaneously broken U(1)' and dark radiation, analyzing its gravitational wave production in light of cosmological constraints.

Findings

Current constraints from N_eff and Lyman-alpha limit gravitational wave signals.

The model's gravitational waves are too weak for future detection.

Secluded dark sectors are unlikely sources of detectable gravitational waves.

Abstract

In this work we study the possibility to detect the gravitational waves generated by a secluded self-interacting dark sector. ``Secluded'' means that the dark sector has almost no portal to the visible sector and thus its entropy is conserved by itself, and ``self-interacting'' means that dark matter in this model has a significant interaction to itself, making it consistent with the small-scale structure observations. A spontaneously broken $U(1)'$ is introduced for the interactions in the dark sector, and nearly massless dark radiation is also introduced to avoid the over-closure problem. Through a parameter space scan, we find that this model is highly constrained by the current observed effective number of neutrinos ($N_{\text{eff}}$) and the large-scale structure observable Lyman-$\alpha$. Combined together, these two constraints make such a secluded self-interacting dark sector almost impossible to generate gravitational waves accessible at future projects like SKA or LISA.