Non-relativistic susceptibility and a dark matter application

TL;DR

This paper investigates non-relativistic susceptibilities relevant for dark matter freeze-out, using lattice simulations and models to confirm the viability of multi-TeV dark matter masses with specific mass degeneracies.

Contribution

It introduces a formalism for non-relativistic susceptibilities in dark matter scenarios and applies it to a Majorana singlet model, supported by lattice simulations.

Findings

Susceptibility dominated by bound states of stop-like mediators.

Masses up to multi-TeV are viable with sufficient dark sector degeneracy.

Formalism validated through lattice simulation and model application.

Abstract

When thermal rate equations are derived for the evolution of slow variables, it is often practical to parametrize the right-hand side with chemical potentials. To close the system, the chemical potentials are subsequently re-expressed in terms of the slow variables, which involves the consideration of a "susceptibility". Here we study a non-relativistic situation in which chemical potentials are large compared with the temperature, as is relevant for late-time pair annihilations in dark matter freeze-out. An order-of-magnitude estimate and a lattice simulation are presented for a susceptibility dominated by bound states of stop-like mediators. After this "calibration", the formalism is applied to a model with Majorana singlet dark matter, confirming that masses up to the multi-TeV domain are viable in the presence of sufficient (though not beyond a limit) mass degeneracy in the dark sector.