# Constraints on Dark Matter-Photon Coupling in the Presence of Time-Varying Dark Energy

## TL;DR

This study extends previous dark matter-photon coupling models by incorporating a time-varying dark energy equation of state, deriving observational constraints, and analyzing implications for cosmological tensions like H0 and sigma8.

## Contribution

It introduces a model with a time-varying dark energy EoS in the DM-photon coupling framework and constrains it using multiple cosmological data sets.

## Key findings

- Mean dark energy EoS today is in the quintessence region.
- No significant change in DM-photon coupling constraints.
- Higher H0 values align with local measurements.

## Abstract

In a recent work [Phys. Rev. D 98, 043521 (2018)], we have investigated a dark matter (DM)-photon coupling model in which the DM decays into photons in the presence of dark energy (DE) with the constant equation of state (EoS) parameter. Here, we study an extension of the DM-photon coupling model by considering a time-varying EoS of DE via Chevalier-Polarski-Linder (CPL) parametrization. We derive observational constraints on the model parameters by using the data from cosmic microwave background (CMB), baryonic acoustic oscillations (BAO), the local value of Hubble constant from Hubble Space Telescope (HST), and large scale structure (LSS) information from the abundance of galaxy clusters, in four different combinations. We find that in the present DM-photon coupling scenario the mean values of $w_{\rm de0}$ are in quintessence region ($w_{\rm de0} > -1$) whereas they were in the phantom region ($w_{\rm de0} < -1$) in our previous study with all data combinations. The constraints on the DM-photon coupling parameter do not reflect any significant deviation from the previous results. Due to the decay of DM into photons, we obtain higher values of $H_0$, consistent with the local measurements, similar to our previous study. But, the time-varying DE leads to lower values of $\sigma_8$ in the DM-photon coupling model with all data combinations, in comparison to the results in our previous study. Thus, allowing time-varying DE in the DM-photon coupling scenario is useful to alleviate the $H_0$ and $\sigma_8$ tensions.