Cosmological bounds on dark matter-photon coupling

Abstract

We investigate an extension of the $\Lambda$CDM model where the dark matter (DM) is coupled to photons, inducing a nonconservation of the numbers of particles for both species, where the DM particles are allowed to dilute throughout the cosmic history with a small deviation from the standard evolution decaying into photons, while the associated scattering processes are assumed to be negligible. In addition, we consider the presence of massive neutrinos with the effective number of species $N_{\rm eff}$ as a free parameter. The effects of the DM-photon coupling on the cosmic microwave background (CMB) and matter power spectra are analyzed. We derive the observational constraints on the model parameters by using the data from CMB, baryonic acoustic oscillation (BAO) measurements, the recently measured new local value of the Hubble constant from the Hubble Space Telescope, and large scale structure (LSS) information from the abundance of galaxy clusters. The DM-photon coupling parameter $\Gamma_{\gamma }$ is constrained to $\Gamma_{\gamma } \leq 1.3 \times10^{-5}$ (at 95\% C.L.) from the joint analysis carried out by using all the mentioned data sets. The neutrino mass scale $\sum m_{\nu}$ upper bounds at 95\% C.L. are obtained as $\sum m_{\nu} \sim 0.9$ eV and $\sum m_{\nu} \sim 0.4$ eV with and without the LSS data, respectively. We observe that the DM-photon coupling cause significant changes in the best fit value of $N_{\rm eff}$ but yields statistical ranges of $N_{\rm eff}$ compatible with the standard predictions, and we do not find any evidence of dark radiation. Due to nonconservation of photons in our model, we also evaluate and analyze the effects on the BAO acoustic scale at the drag epoch. The DM-photon coupling model yields high values of Hubble constant consistent with the local measurement, and thus alleviates the tension on this parameter.