Asymmetric Dark Matter and Dark Radiation

TL;DR

This paper explores a model of asymmetric dark matter where the mediator decays into dark radiation, affecting early universe signals and offering new ways to probe dark sector interactions through cosmological observations.

Contribution

It introduces a scenario where dark matter annihilates into dark radiation, impacting cosmological measurements and providing novel insights into dark sector structure.

Findings

Dark radiation influences BBN and CMB signals.

Planck measurements can constrain dark sector interactions.

Matter power spectrum analysis limits DM-Dark Radiation interactions.

Abstract

Asymmetric Dark Matter (ADM) models invoke a particle-antiparticle asymmetry, similar to the one observed in the Baryon sector, to account for the Dark Matter (DM) abundance. Both asymmetries are usually generated by the same mechanism and generally related, thus predicting DM masses around 5 GeV in order to obtain the correct density. The main challenge for successful models is to ensure efficient annihilation of the thermally produced symmetric component of such a light DM candidate without violating constraints from collider or direct searches. A common way to overcome this involves a light mediator, into which DM can efficiently annihilate and which subsequently decays into Standard Model particles. Here we explore the scenario where the light mediator decays instead into lighter degrees of freedom in the dark sector that act as radiation in the early Universe. While this assumption makes indirect DM searches challenging, it leads to signals of extra radiation at BBN and CMB. Under certain conditions, precise measurements of the number of relativistic species, such as those expected from the Planck satellite, can provide information on the structure of the dark sector. We also discuss the constraints of the interactions between DM and Dark Radiation from their imprint in the matter power spectrum.