Constraints on Warm Dark Matter models from high-redshift long gamma-ray bursts

TL;DR

This study uses high-redshift gamma-ray burst data to place new lower limits on the mass of warm dark matter particles, demonstrating GRBs' effectiveness in probing early universe structures.

Contribution

It provides the first constraints on warm dark matter particle mass using high-redshift GRB observations, accounting for astrophysical uncertainties.

Findings

Constraints on $m_{x}$ are $ extgreater 1.6$-1.8 keV at 95% C.L.

Future observations could improve constraints to $m_{x} extgreater 2.3$ keV.

GRBs are shown to be a powerful probe of high-redshift structure formation.

Abstract

Structures in Warm Dark Matter (WDM) models are exponentially suppressed below a certain scale, characterized by the dark matter particle mass, $m_{\rm x}$. Since structures form hierarchically, the presence of collapsed objects at high-redshifts can set strong lower limits on $m_{\rm x}$. We place robust constraints on $m_{\rm x}$ using recent results from the {\it Swift} database of high-redshift gamma-ray bursts (GRBs). We parameterize the redshift evolution of the ratio between the cosmic GRB rate and star formation rate (SFR) as $\propto (1+z)^\alpha$, thereby allowing astrophysical uncertainties to partially mimic the cosmological suppression of structures in WDM models. Using a maximum likelihood estimator on two different $z>4$ GRB subsamples (including two bursts at $z>8$), we constrain $m_{\rm x} \gtrsim 1.6$-1.8 keV at 95% C.L., when marginalized over a flat prior in $\alpha$. We further estimate that 5 years of a SVOM-like mission would tighten these constraints to $m_{\rm x} \gtrsim 2.3 $ keV. Our results show that GRBs are a powerful probe of high-redshift structures, providing robust and competitive constraints on $m_{\rm x}$.