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, once more, to sterile neutrinos which can constitute cold non-thermal dark matter for a wide range of masses, including the keV scale. 

Biography

Dr. Fotis Koutroulis is a postdoc at the Institute of High Energy Physics, CAS, and an affiliated member of CCAST. He received his PhD in Physics from the National Technical University of Athens in 2021. After completing his doctorate, he held a postdoctoral position at the Institute of Theoretical Physics, University of Warsaw, before joining IHEP. His research interests lie at the interface of particle physics and early universe cosmology, with a focus on physics beyond the Standard Model, dark matter, and cosmological probes of new physics.

Inviter: Shi Pi