Constraining hot dark matter sub-species with weak lensing and the cosmic microwave background radiation

¹ Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
² Université Paris-Saclay, Université Paris Cité, CEA, CNRS, Astrophysique, Instrumentation et Modélisation Paris-Saclay, 91191 Gif-sur-Yvette, France
e-mail: fabian.hervaspeters@cea.fr
³ Nordita, KTH Royal Institute of Technology and Stockholm University, Hannes Alfvens väg 12, 106 91 Stockholm, Sweden
⁴ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
⁵ Dipartimento di Fisica, Università degli studi di Genova, and INFN-Sezione di Genova, Via Dodecaneso 33, 16146 Genova, Italy
⁶ SISSA, International School for Advanced Studies, Via Bonomea 265, 34136 Trieste, Italy

Received: 9 January 2024
Accepted: 16 April 2024

Abstract

Although it is well known that the bulk of dark matter (DM) has to be cold, the existence of an additional sub-dominant, hot species remains a valid possibility. In this paper we investigate the potential of the cosmic shear power spectrum to constrain such a mixed (hot plus cold) DM scenario with two additional free parameters, the hot-to-total DM fraction (f_hdm) and the thermal mass of the hot component (m_hdm). Running a Bayesian inference analysis for both the Kilo-Degree Survey cosmic shear data (KiDS-1000) as well as the cosmic microwave background (CMB) temperature and polarisation data from Planck, we derive new constraints for the mixed DM scenario. We find a 95% confidence limit of f_hdm < 0.08 for a very hot species of m_hdm ≤ 20 eV. This constraint is weakened to f_hdm < 0.25 for m_hdm ≤ 80 eV. Scenarios with masses above m_hdm ∼ 200 eV remain unconstrained by the data. Next to providing limits, we investigate the potential of mixed DM to address the clustering (or S₈) tension between lensing and the CMB. We find a reduction of the 2D (Ω_m − S₈) tension from 2.9σ to 1.6σ when going from a pure cold DM to a mixed DM scenario. When computing the 1D Gaussian tension on S₈ the improvement is milder, from 2.4σ to 2.0σ.