Temperature Power Law of Equilibrium Heavy Particle Density

TL;DR

This paper derives a power law temperature dependence for the energy density of heavy particles in thermal equilibrium, challenging the traditional exponential suppression estimate and impacting dark matter relic abundance calculations.

Contribution

It provides a second-order thermal field theory calculation showing a power law behavior, contrasting with the ideal gas approximation.

Findings

Power law temperature dependence of heavy particle energy density at low temperatures.

Supports previous Hartree approximation results.

Implications for dark matter relic abundance calculations.

Abstract

A standard calculation of the energy density of heavy stable particles that may pair-annihilate into light particles making up thermal medium is performed to second order of coupling, using the technique of thermal field theory. At very low temperatures a power law of temperature is derived for the energy density of the heavy particle. This is in sharp contrast to the exponentially suppressed contribution estimated from the ideal gas distribution function. The result supports a previous dynamical calculation based on the Hartree approximation, and implies that the relic abundance of dark matter particles is enhanced compared to that based on the Boltzmann equation.