Lyman-alpha constraints on warm and on warm-plus-cold dark matter models

TL;DR

This paper revisits Lyman-alpha constraints on warm dark matter models, deriving new bounds for pure and mixed cold-plus-warm models by combining observational data with rigorous systematic analysis.

Contribution

It provides updated bounds on warm dark matter particle masses and fractions, including for mixed models, using comprehensive statistical approaches and multiple data sets.

Findings

Pure Lambda-WDM mass bound: >8 keV (99.7% CL)

Mixed models allow any mass if warm fraction <0.6 (99.7% CL)

Any mass is allowed if warm fraction <0.35 (Bayesian 95% CI)

Abstract

We revisit Lyman-alpha bounds on the dark matter mass in Lambda Warm Dark Matter (Lambda-WDM) models, and derive new bounds in the case of mixed Cold plus Warm models (Lambda-CWDM), using a set up which is a good approximation for several theoretically well-motivated dark matter models. We combine WMAP5 results with two different Lyman-alpha data sets, including observations from the Sloan Digital Sky Survey. We pay a special attention to systematics, test various possible sources of error, and compare the results of different statistical approaches. Expressed in terms of the mass of a non-resonantly produced sterile neutrino, our bounds read m_NRP > 8 keV (frequentist 99.7% confidence limit) or m_NRP > 12.1 keV (Bayesian 95% credible interval) in the pure Lambda-WDM limit. For the mixed model, we obtain limits on the mass as a function of the warm dark matter fraction F_WDM. Within the mass range studied here (5 keV < m_NRP < infinity), we find that any mass value is allowed when F_WDM < 0.6 (frequentist 99.7% confidence limit); similarly, the Bayesian joint probability on (F_WDM, 1/m_NRP) allows any value of the mass at the 95% confidence level, provided that F_WDM < 0.35.