The photon self-energy and its implications on dark photon searches

Hugo Schérer ( Université McGill )

The nature of dark matter is one of the greatest mysteries of modern cosmology and its measured properties can only be explained by physics beyond the Standard Model. Dark matter could reside in a "dark sector" that contains a "dark photon," a spin-1 gauge boson that would couple weakly to the Standard Model photon. This coupling results in interesting phenomenology in a variety of physical contexts. In many environments, such as the early universe or stars, finite temperature effects modify the properties of particles, including their dispersion relations. In particular, the Standard Model photon acquires an effective mass, or self-energy. This impacts its coupling to the dark photon in qualitatively new ways. In this talk, I will present new analytic expressions for the photon self-energy. I will discuss some bounds on the dark photon's parameters from cosmology in which the photon self-energy plays a crucial role.