NBIA Seminar: Miguel Escudero

Neutrinos are a key (although implicit) ingredient of the standard cosmological model, LambdaCDM. Firstly, neutrinos directly participate in Big Bang Nucleonsynthesis, and secondly, they represent 40% of the energy density of the Universe after electron positron annihilation up to almost matter radiation equality. The latter fact makes neutrinos a necessary element to understand the very precise observations of the Cosmic Microwave Background.

In this seminar, I will review the cosmological implications of neutrinos. I will explain how current cosmological observations can be used to constrain their masses and their abundances. In particular, I will discuss various cosmological settings where the typically very stringent constraint on their masses can be substantially relaxed. I will then show how measurements of the effective number of neutrino species in the early Universe can place stringent bounds on many extensions of the Standard Model of particle physics. I will finish by reviewing the role neutrinos can play with regards to the outstanding Hubble tension. In particular, I will show that pseudo-Goldstone bosons (majorons) interacting with neutrinos right before recombination represent a well motivated possibility to ameliorate the Hubble tension.