New Constraints on the Mass of Fermionic Dark Matter from Dwarf Spheroidal Galaxies

TL;DR

This paper refines phase-space constraints on fermionic dark matter mass using dwarf spheroidal galaxies, improving analysis methods and deriving new bounds for various dark matter production scenarios.

Contribution

It introduces an improved Jeans analysis and compares phase-space bounds with other observational limits for sterile neutrinos.

Findings

Lower bound of 0.18 keV for fermionic dark matter from Pauli principle

Stronger bounds for thermal relics at 0.59 keV (68% CL)

Constraints on sterile neutrinos at 2.80 keV (68% CL)

Abstract

Dwarf spheroidal galaxies are excellent systems to probe the nature of fermionic dark matter due to their high observed dark matter phase-space density. In this work, we review, revise and improve upon previous phase-space considerations to obtain lower bounds on the mass of fermionic dark matter particles. The refinement in the results compared to previous works is realised particularly due to a significantly improved Jeans analysis of the galaxies. We discuss two methods to obtain phase-space bounds on the dark matter mass, one model-independent bound based on Pauli's principle, and the other derived from an application of Liouville's theorem. As benchmark examples for the latter case, we derive constraints for thermally decoupled particles and (non-)resonantly produced sterile neutrinos. Using the Pauli principle, we report a model-independent lower bound of $m \geq 0.18\,\mathrm{keV}$ at 68% CL and $m \geq 0.13\,\mathrm{keV}$ at 95% CL. For relativistically decoupled thermal relics, this bound is strengthened to $m \geq 0.59\,\mathrm{keV}$ at 68% CL and $m \geq 0.41\,\mathrm{keV}$ at 95% CL, whilst for non-resonantly produced sterile neutrinos the constraint is $m \geq 2.80\,\mathrm{keV}$ at 68% CL and $m \geq 1.74\,\mathrm{keV}$ at 95% CL. Finally, the phase-space bounds on resonantly produced sterile neutrinos are compared with complementary limits from X-ray, Lyman-$\alpha$ and Big Bang Nucleosynthesis observations.