Does the Reionization Model Influence the Constraints on Dark Matter Decay or Annihilation?

TL;DR

This study investigates how different reionization models affect constraints on dark matter decay or annihilation, finding minimal influence on parameter limits when combining multiple cosmological observations.

Contribution

It compares constraints on dark matter annihilation using different reionization models, demonstrating that model choice has limited impact on parameter bounds.

Findings

Reionization models have less than 2.5% impact on dark matter constraints.

Combined data yields optical depth τ≈0.0571 with tight uncertainties.

Upper limit on dark matter annihilation parameter is approximately 2.78×10^{-24}.

Abstract

If dark matter decay or annihilate, a large amount of energy and particles would be released into the cosmic plasma. Therefore, they could modify the thermal and ionization history of our universe, then leave footprints on the cosmic microwave background power spectra. In this paper, we take dark matter annihilation as an example and investigate whether different reionization models influence the constraints on dark matter annihilation. We consider the ionization history including both dark matter annihilation and star formation, then put constraints on DM annihilation. Combining the latest Planck data, BAO data, SNIa measurement, $Q_\text{HII}$ constraints from observations of quasars, as well as the star formation rate density from UV and IR data, the optical depth is $\tau=0.0571^{+0.0005}_{-0.0006}$ at 68$\%$C.L. and the upper limit of $\epsilon_0 f_d$ reads $2.7765\times 10^{-24}$ at 95$\%$C.L.. By comparison, we also constrain dark matter annihilation in the instantaneous reionization model from the same data combination except the $Q_\text{HII}$ constraints and star formation rate density. We get $\tau=0.0559^{+0.0069}_{-0.0076}$ at 68$\%$C.L. and the upper limit of $\epsilon_0 f_d$ is $2.8468\times 10^{-24}$ at 95$\%$C.L.. %, which is $2.5\%$ higher than the results in the previous model. This indicates various reionization models have little influence ($\lesssim 2.5\%$) on constraining parameters of dark matter decay or annihilation.