T-2, Nuclear and Particle Physics, Astrophysics and Cosmology

Neutrino Physics during the epoch of Recombination

Evan Grohs

In this talk, I will discuss Cosmic Microwave Background observables of interest to neutrino physics. Specifically, I address two such observables: Neff, normally used as a parameter in the radiation energy density; and Σmν, the sum of the active neutrino masses. There exists a surprising and counter-intuitive result for how a non-zero Σmνaffects Neff. Instead of treating Neffas a parameter in the radiation energy density, I look at how the sound horizon and especially the diffusion length change with the addition of extra energy density. The increase in energy density due to non-zero Σmνleads to a larger free-electron fraction, thereby changing the diffusion length. This leads to a different recombination history of the universe which lowers Neff, as opposed to the expectation of an increase in Neff from extra energy density. Furthermore, this counter-intuitive result is present in other exotic cosmologies, such as non-zero lepton number or the presence of light sterile neutrinos. This work is part of a long-term project on investigating early-universe observables in beyond- standard-model physics.


Contact Us | Careers | Bradbury Science Museum | Emergencies | Inside LANL | Maps | Site Feedback | SSL Portal | Training

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA© Copyright 2010-11 LANS, LLC All rights reserved | Terms of Use | Privacy Policy