Spectral distortion constraints on photon injection from low-mass decaying particles

Understand

Spectral distortions (SDs) of the cosmic microwave background (CMB) provide a powerful tool for studying particle physics.

• Here we compute the distortion signals from decaying particles that convert directly into photons at different epochs during cosmic history, focusing on injection energies $E_\mathrm{inj}\lesssim 20\,\mathrm{keV}$.
• We deliver a comprehensive library of SD solutions that can be used to study a wide range of particle physics scenarios.
• We use {\tt CosmoTherm} to compute the SD signals, including effects on the ionization history and opacities of the Universe.