Self-Interacting Dark Sectors in Supernovae Can Behave as a Relativistic Fluid

TL;DR

This paper investigates how self-interacting dark sectors, specifically millicharged particles and dark photons, influence supernova bounds, revealing that such particles can behave as a relativistic fluid and affect energy deposition constraints.

Contribution

It introduces a novel analysis of supernova bounds considering self-interacting dark particles forming a relativistic fluid, extending the understanding of dark sector constraints beyond free-streaming assumptions.

Findings

Dark particles form a relativistic fluid in supernovae if self-coupling is strong.

New bounds on dark sector parameters from energy deposition in supernova mantles.

Cooling bounds from SN 1987A remain unaffected in the free-streaming regime.

Abstract

We revisit supernova (SN) bounds on a hidden sector consisting of millicharged particles $\chi$ and a massless dark photon. Unless the self-coupling is fine-tuned to be small, rather than exiting the SN core as a gas, the particles form a relativistic fluid and subsequent dark QED fireball, streaming out against the drag due to the interaction with matter. Novel bounds due to excessive energy deposition in the mantle of low-energy SNe can be obtained. The cooling bounds from SN 1987A are unexpectedly not affected in the free-streaming regime. The inclusion of $\chi\bar{\chi}\rightarrow \rm SM$ substantially modifies the constraints in the trapping regime, which can only be treated hydrodynamically. Our results can be adapted to generic sub-GeV self-interacting dark sectors.