Dynamics of the pseudo-FIMP in presence of a thermal Dark Matter

TL;DR

This paper introduces the concept of pseudo-FIMP (pFIMP) dark matter, where a feebly interacting component reaches equilibrium through interaction with a thermal dark matter partner, affecting its freeze-out behavior.

Contribution

It defines the pFIMP category, analyzes its properties using coupled Boltzmann equations, and provides a model-independent framework and a concrete example.

Findings

pFIMP can equilibrate via its interaction with thermal DM

pFIMP exhibits unique freeze-out characteristics influenced by its partner

The framework is applicable to various models of multi-component dark matter

Abstract

We demonstrate that in a two component dark matter (DM) set up, when DM$_1$ is equilibrated with the thermal bath, the other DM$_2$, in spite of having feeble or negligible interaction with the SM particles, can be brought to equilibrium just by having sizeable interaction with DM$_1$. We propose that such DM candidates (DM$_2$) should be classified into a category called pseudo-FIMP (pFIMP) having unique freeze-out characteristics which depend on the thermal DM partner. The draft elaborates upon the pFIMP properties from a generic coupled Boltzmann Equations (cBEQ) in a model independent way, followed by a concrete model illustration.