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Neutrinos in Cosmology

Neutrinos are a key (although implicit) ingredient of the standard cosmological model, LambdaCDM. Firstly, neutrinos directly participate in neutron freeze out during BBN, 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 CMB observations.

In this talk, I will review the cosmological implications of neutrinos. I will explain how current cosmological observations can be used to constrain their masses, their abundances, and their properties — such as their interaction rate with other species. In particular, I will highlight that the typically very stringent constraint on their masses can be substantially relaxed if neutrinos decay on cosmological timescales. I will then show how BBN and Neff’s measurements place stringent bounds on many extensions of the Standard Model of particle physics. I will finish by reviewing the role neutrinos can play with regard to the outstanding Hubble tension. In particular, I will show that pseudogoldstone bosons (majorons) interacting with neutrinos right before recombination represent a well-motivated possibility to ameliorate (and potentially solve) the Hubble tension.

McDonald Insititute seminars bring together experimental and theoretical astroparticle physicists and astronomers. They are held approximately fortnightly, September to November and January to March, and on an ad hoc basis outside of term. They currently take place on Tuesdays at 2:30 PM on Zoom. Contact Aaron Vincent if you would like to attend.

https://www.physics.queensu.ca/facultysites/vincent/seminars/