Is it Mixed dark matter or neutrino masses?

TL;DR

This paper investigates how a mixed dark matter scenario with photon interactions can mimic effects of neutrino masses on the matter power spectrum, and discusses how future measurements could distinguish between these possibilities.

Contribution

It introduces a model of mixed dark matter with photon interactions and analyzes its degeneracy with neutrino mass effects using current and future cosmological data.

Findings

Dark matter-photon interactions can mimic neutrino mass effects on the matter power spectrum.

Current Planck data cannot constrain the interaction strength when the interacting dark matter fraction is small.

Future DESI measurements could help disentangle dark matter properties from neutrino masses, especially if the interaction rate is near current limits.

Abstract

In this paper, we explore a scenario where the dark matter is a mixture of interacting and non interacting species. Assuming dark matter-photon interactions for the interacting species, we find that the suppression of the matter power spectrum in this scenario can mimic that expected in the case of massive neutrinos. Our numerical studies include present limits from Planck Cosmic Microwave Background data, which render the strength of the dark matter photon interaction unconstrained when the fraction of interacting dark matter is small. Despite the large entangling between mixed dark matter and neutrino masses, we show that future measurements from the Dark Energy Instrument (DESI) could help in establishing the dark matter and the neutrino properties simultaneously, provided that the interaction rate is very close to its current limits and the fraction of interacting dark matter is at least of $\mathcal{O}\left(10\%\right)$. However, for that region of parameter space where a small fraction of interacting DM coincides with a comparatively large interaction rate, our analysis highlights a considerable degeneracy between the mixed dark matter parameters and the neutrino mass scale.