Constraining broad photon spectrum injections from exotic and astrophysical sources

We study the evolution of photon injections with a power-law type spectrum inserted at various epochs of the universe, and obtain constraints on their parameter space from multiple different cosmological probes. Our work is motivated by the realistic possibility of having extended photon spectra from astrophysical and exotic sources. Going beyond a $\delta$-function like approximation, the physics becomes richer and the constraining power of cosmological probes starts to depend on the photon injection history in a complex way. As a toy model, we first consider a decaying particle scenario, and then generalize to a more model independent power law type injection in redshift. Different combinations of our parameters can be mapped to a wide variety of realistic astrophysical and exotic sources, providing useful benchmarks for study in future work.