[Paper Review] Joint constraints on thermal relic dark matter from a selection of astrophysical probes

Wolfgang Enzi, Riccardo Murgia+11 more|arXiv (Cornell University)|Nov 24, 2020

Dark Matter and Cosmic Phenomena4 citations

TL;DR

This study combines strong gravitational lensing, the Lyman-alpha forest, and Milky Way satellite counts to derive joint constraints on warm dark matter (WDM) using thermal relic particle assumptions. It sets a 95% confidence upper limit of λ_hm ≤ 0.079 Mpc h⁻¹ (M_hm ≤ 6.733 keV), ruling out the 7.1 keV sterile neutrino and ETHOS-4 self-interacting dark matter models, and highlights the need for tighter constraints at lower half-mode scales.

ABSTRACT

We derive joint constraints on the warm dark matter (WDM) half-mode scale by combining the analyses of a selection of astrophysical probes: strong gravitational lensing with extended sources, the Lyman-$\alpha$ forest, and the number of luminous satellites in the Milky Way. We derive an upper limit of $\lambda_{ m hm}=0.079{ m~Mpc~h^{-1} }$ at the 95 per cent confidence level, which we show to be stable for a broad range of prior choices. Assuming a Planck cosmology and that WDM particles are thermal relics, this corresponds to an upper limit on the half-mode mass of $M_{ m hm } 6.733 { m~keV}$, both at the 95 per cent level. We find that models with $\lambda_{ m hm}> 0.220 { m~Mpc~h^{-1} }$ (corresponding to $m_{ m th }> 2.682 { m~keV}$ and $M_{ m hm} 10$, we rule out the $7.1 { m~keV}$ sterile neutrino dark matter model, which presents a possible explanation to the unidentified $3.55 { m~keV}$ line. The inferred 95 percentiles suggest that we further rule out the ETHOS-4 model of self-interacting DM. Our results highlight the importance of extending the current constraints to lower half-mode scales. We address important sources of systematic errors and provide prospects for how constraints of these probes can be improved upon in the future.

Motivation & Objective

• To derive joint constraints on warm dark matter (WDM) using multiple astrophysical probes to improve robustness against systematic uncertainties.
• To test the viability of thermal relic WDM models, particularly sterile neutrinos and self-interacting dark matter, against observational data.
• To assess the stability of constraints under broad prior choices and identify key sources of systematic error.
• To provide a pathway for improving future constraints through enhanced data and modeling from current and upcoming probes.

Proposed method

• Combines strong gravitational lensing with extended sources to probe small-scale power suppression in the matter power spectrum.
• Incorporates constraints from the Lyman-alpha forest to probe the thermal history and small-scale structure formation.
• Uses the observed number of luminous satellites in the Milky Way to constrain the subhalo mass function and WDM suppression scale.
• Applies a Bayesian framework to combine these probes under a Planck cosmology, assuming WDM particles are thermal relics.
• Employs the half-mode scale λ_hm as a key parameter to characterize WDM suppression, with M_hm derived from λ_hm via standard WDM scaling relations.
• Performs sensitivity tests across a broad range of prior distributions to assess stability of the final constraints.

Experimental results

Research questions

• RQ1 What is the tightest joint constraint on the warm dark matter half-mode scale λ_hm when combining lensing, Lyman-alpha forest, and satellite counts?
• RQ2 How stable are these constraints under variations in prior assumptions for the WDM model parameters?
• RQ3 Which thermal relic WDM models—specifically the 7.1 keV sterile neutrino and ETHOS-4 self-interacting dark matter—are ruled out by the combined data?
• RQ4 What are the dominant systematic uncertainties affecting current WDM constraints from these probes?
• RQ5 How can future improvements in data and modeling tighten constraints on the half-mode scale at lower values?

Key findings

• The joint analysis yields a 95% confidence upper limit of λ_hm ≤ 0.079 Mpc h⁻¹, which is stable across a broad range of prior choices.
• This corresponds to an upper limit on the half-mode mass of M_hm ≤ 6.733 keV at the 95% confidence level under Planck cosmology.
• The 7.1 keV sterile neutrino dark matter model is ruled out at the 95% confidence level due to its predicted half-mode scale exceeding the derived upper limit.
• The ETHOS-4 self-interacting dark matter model is also ruled out at the 95% confidence level based on the inferred constraints.
• The results emphasize the importance of extending constraints to lower half-mode scales to further test WDM and alternative dark matter models.
• Systematic errors from probe-specific uncertainties are identified and addressed, with prospects for future improvements through higher-resolution data and refined modeling.