Title: The Cosmological Neff: A Powerful Probe of Neutrino Physics

Host: Yuval Grossman

Abstract: Modern cosmology tells us that there are three species of neutrinos. In terms of a commonly used cosmological observable, it is Neff=3.045. Why 3.045? Why not an integer? Can this observable really be measured so precisely? How likely could this be affected by BSM physics related to neutrinos? In this talk, I will provide a brief introduction to neutrino cosmology, with a focus on one of its most important observables, Neff. I will demonstrate, through some of my recent work, that precision measurements of Neff in next-generation CMB experiments may be able to answer crucial questions such as whether neutrinos are Dirac or Majorana fermions, and how they may interact with dark matter and other dark sector particles.

Talk based on 2312.1715, 2307.13967, 2211.04669, 2110.09883, 2011.13059, and 2005.01629.