Speaker
Description
Future cosmological observatories, such as CMB-S4, the Thirty Meter Telescope, and the Vera Rubin Observatory, will give the highest precision data on the universe ever measured. The convolution of this data may allow theorists to posit new Beyond Standard Model (BSM) physics in operation during earlier phases of the universe. In the work presented here, we focus on the transition of neutrinos from the tightly-coupled regime of equilibrium to the decoupled epoch of free-streaming. Neutrino decoupling precedes the freeze-out of weak isospin-changing and nuclear reactions. The out-of-equilibrium neutrino distributions ultimately influence late time observables such as primordial abundances and radiation energy density. We use a parameterization of the neutrino distribution fields to describe the time evolution of those functions during this weak decoupling period. Our model is an excellent description of the system in the energy region that captures 64$\%$ of the total neutrino density. Within this region, our polynomial fitting never deviates more than 0.05$\%$. We discuss how the coefficients of the parameterization are related to the expected number, energy, and energy fluctuations of the system. Our results and methodology have implications for characterizing the standard or BSM theories of cosmology.
