Precision Early Universe Thermodynamics made simple: $N_{rm eff}$ and Neutrino Decoupling in the Standard Model and beyond. (arXiv:2001.04466v1 [hep-ph])

<a href="http://arxiv.org/find/hep-ph/1/au:+Escudero_M/0/1/0/all/0/1">Miguel Escudero</a>

Precision measurements of the number of effective relativistic neutrino

species and the primordial element abundances require accurate theoretical

predictions for early Universe observables in the Standard Model and beyond.

Given the complexity of accurately modelling the thermal history of the early

Universe; in this work, we extend a previous method presented by the author to

obtain simple, fast and accurate early Universe thermodynamics. The method is

based upon the approximation that all relevant species can be described by

thermal equilibrium distribution functions characterized by a temperature and a

chemical potential. We apply the method to neutrino decoupling in the Standard

Model and find $N_{rm eff}^{rm SM} = 3.045$ — a result in excellent

agreement with previous state-of-the-art calculations. We apply the method to

study the thermal history of the Universe in the presence of a very light

($1,text{eV}

Precision measurements of the number of effective relativistic neutrino

species and the primordial element abundances require accurate theoretical

predictions for early Universe observables in the Standard Model and beyond.

Given the complexity of accurately modelling the thermal history of the early

Universe; in this work, we extend a previous method presented by the author to

obtain simple, fast and accurate early Universe thermodynamics. The method is

based upon the approximation that all relevant species can be described by

thermal equilibrium distribution functions characterized by a temperature and a

chemical potential. We apply the method to neutrino decoupling in the Standard

Model and find $N_{rm eff}^{rm SM} = 3.045$ — a result in excellent

agreement with previous state-of-the-art calculations. We apply the method to

study the thermal history of the Universe in the presence of a very light

($1,text{eV}<m_phi < 1,text{MeV}$) and weakly coupled ($lambda lesssim

10^{-9}$) neutrinophilic scalar. We find our results to be in excellent

agreement with the solution to the exact Liouville equation. Finally, we

release a code: NUDEC_BSM (available in both Mathematica and Python formats),

with which neutrino decoupling can be accurately and efficiently solved in the

Standard Model and beyond: https://github.com/MiguelEA/nudec_BSM .

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