Limit on the dark matter mass from its interaction with photons

Understand

In this work, we explore the phenomenology of generalized dark matter (GDM) which interacts with photons ($\gamma$).

• We assume that DM establishes elastic scattering with $\gamma$ when it has already become nonrelativistic, otherwise the abundance of DM today is disfavored by current observations.
• Within this scenario, the equation of state (EoS) of DM is determined by its mass ($m_\chi$) and the DM-$\gamma$ scattering cross-section.
• The distinctive imprints of a nonzero EoS of DM on CMB angular power spectrum allow us to set a lower limit on $m_\chi$ with Planck 2018 data alone, i.e., $m_{\chi} > 8.7$ keV at $95\%$ C.L.