Light Dark Matter in a Blazar-heated Universe

TL;DR

This paper explores how plasma effects from blazar emissions can influence the intergalactic medium, dark matter properties, and cosmic structure formation, suggesting new avenues for understanding dark matter and cosmological small-scale issues.

Contribution

It proposes that plasma instabilities from blazar emissions significantly impact the IGM, dark matter constraints, and the thermal history of the universe, offering novel insights into cosmological small-scale problems.

Findings

Plasma effects can suppress structure formation in underdense regions.

Constraints on light axion-like particles as dark matter candidates.

Blazar heating influences the thermal history and small-scale structure.

Abstract

Prompt emissions from TeV blazars pair produce off the extragalactic background light and the highly energetic resulting pair beams then cascade through inverse Compton scattering to give rise to secondary gamma-rays. Such reprocessed cascade emission that can be associated with individual blazar sources has not been detected thus far. The absence of pair halos around these sources, along with the non-observation of isotropic gamma-ray background excess, seems to suggest that collective plasma effects, such as beam-plasma instabilities, can play a crucial role in alleviating this GeV-TeV tension by transferring the energy from the pair beams into the background plasma of the intergalactic medium (IGM). This has profound implications not only for TeV astrophysics, but also the strength of the intergalactic magnetic field and properties of dark matter (DM). A direct consequence of the instability losses and IGM heating is the modification of thermal history at late times, which suppresses structure formation particularly in baryonically underdense regions, potentially holding a clue towards resolving the small-scale crisis in cosmology. In a blazar-heated universe, the observation of dwarf galaxies and Lyman-$\alpha$ measurements present a favoured mass range for DM candidates such as light axion-like particles.