The annihilation and decay of dark matter (DM) during the dark ages can leave imprints in the cosmic microwave background (CMB) radiation by altering the cosmic reionization process. CMB polarization anisotropy can be sensitive to such energy injection at higher redshift and therefore helps reducing degeneracy between spectral parameters in $\mathrm{\Lambda }\mathrm{CDM}$ and other astrophysical parameters. In light of several upcoming CMB polarization experiments, such as AdvACTPol, AliCPT, CLASS, Simons Observatory, Simons Array, SPT-3G, we forecast their prospective sensitivity in probing dark matter annihilation and decay signals. We find that future missions have 95% C.L. projected limits on DM decay and annihilation rates to orders of ${\mathrm{\Gamma }}_{\chi }({\tau }_{\chi }^{-1})\sim {10}^{-27}{\mathrm{s}}^{-1}$ and $⟨\sigma v⟩/m_{\chi }\sim {10}^{-29}{\mathrm{cm}}^3{\mathrm{s}}^{-1}{\mathrm{GeV}}^{-1}$, respectively, significantly improving the sensitivity to DM from current experimental bounds.

• Received 10 March 2020
• Accepted 20 October 2020

DOI:https://doi.org/10.1103/PhysRevD.102.103005