On the Sunyaev-Zel'dovich effect from dark matter annihilation or decay in galaxy clusters

TL;DR

This paper assesses the potential for detecting the Sunyaev-Zel'dovich effect caused by dark matter annihilation or decay in galaxy clusters, concluding it is far below current and future experimental sensitivities due to very low optical depths.

Contribution

The study provides a detailed analysis showing the SZ effect from dark matter processes is negligible compared to thermal electrons, with analytical formulas for quick estimates based on DM properties.

Findings

Optical depth from DM is much smaller than thermal electrons.

Current and future experiments cannot detect the SZ effect from DM.

Spatial diffusion creates a core in electron distribution, limiting detection improvements.

Abstract

We revisit the prospects for detecting the Sunyaev Zel'dovich (SZ) effect induced by dark matter (DM) annihilation or decay. We show that with standard (or even extreme) assumptions for DM properties, the optical depth associated with relativistic electrons injected from DM annihilation or decay is much smaller than that associated with thermal electrons, when averaged over the angular resolution of current and future experiments. For example, we find: $\tau_{\rm DM} \sim 10^{-9}-10^{-5}$ (depending on the assumptions) for $\mchi = 1$ GeV and a density profile $\rho\propto r^{-1}$ for a template cluster located at 50 Mpc and observed within an angular resolution of $10"$, compared to $\tau_{\rm th}\sim 10^{-3}-10^{-2}$. This, together with a full spectral analysis, enables us to demonstrate that, for a template cluster with generic properties, the SZ effect due to DM annihilation or decay is far below the sensitivity of the Planck satellite. This is at variance with previous claims regarding heavier annihilating DM particles. Should DM be made of lighter particles, the current constraints from 511 keV observations on the annihilation cross section or decay rate still prevent a detectable SZ effect. Finally, we show that spatial diffusion sets a core of a few kpc in the electron distribution, even for very cuspy DM profiles, such that improving the angular resolution of the instrument, e.g. with ALMA, does not necessarily improve the detection potential. We provide useful analytical formulae parameterized in terms of the DM mass, decay rate or annihilation cross section and DM halo features, that allow quick estimates of the SZ effect induced by any given candidate and any DM halo profile.