Maximally self-interacting dark matter: models and predictions

TL;DR

This paper explores self-interacting dark matter models with near-maximal scattering cross sections, analyzing their velocity dependence, model parameters, and implications for cosmology and particle physics.

Contribution

It identifies model parameters that saturate the Unitarity bound in SIDM models and discusses their implications for cosmology and experiments.

Findings

Self-interaction cross sections can nearly saturate the Unitarity bound.

Models predict strong velocity dependence across astrophysical scales.

Implications for H0 tension and direct detection are discussed.

Abstract

We study self-interacting dark matter (SIDM) scenarios, where the $s$-wave self-scattering cross section almost saturates the Unitarity bound. Such self-scattering cross sections are singly parameterized by the dark matter mass, and are featured by strong velocity dependence in a wide range of velocities. They may be indicated by observations of dark matter halos in a wide range of masses, from Milky Way's dwarf spheroidal galaxies to galaxy clusters. We pin down the model parameters that saturates the Unitarity bound in well-motivated SIDM models: the gauged $L_{\mu} - L_{\tau}$ model and composite asymmetric dark matter model. We discuss implications and predictions of such model parameters for cosmology like the $H_{0}$ tension and dark-matter direct-detection experiments, and particle phenomenology like the beam-dump experiments.