"Theory of Particle Physics and Cosmology" Seminar

In this work we consider cosmological gravitational production of Dirac sterile neutrinos as dark matter candidates during and after inflation. In the former, the Higgs field experiences large quantum fluctuations driving its average field value to the Hubble scale and above facilitating the sterile neutrino production. However, the production efficiency due to classical gravity still remains suppressed compared to the standard freeze-in mechanism. Quantum gravitational effects, on the other hand, are expected to break conformal invariance of the fermion sector by the Planck scale-suppressed operators irrespective of the mass. We find that such operators are very efficient in fermion production immediately after inflation, generating a significant background of stable or long-lived feebly interacting particles. This applies, in particular, to sterile neutrinos which can constitute cold non-thermal dark matter for a wide range of masses, including the keV scale.