The Universe at the MeV era: neutrino evolution and cosmological observables

Neutrino physics in the early Universe is key to our understanding of later cosmological stages, such as primordial nucleosynthesis (BBN) or the formation of large-scale structures. The coming decade promises new experimental results to explore and constrain cosmological models even more precisely -...

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Bibliographic Details
Published inarXiv.org
Main Author Froustey, Julien
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 14.09.2022
Subjects
Antineutrinos
Astronomical models
Big bang cosmology
Cosmology
Decoupling
Deuterium
Evolution
Flavors
Kinetic equations
Neutrinos
Nuclear fusion
Nuclei (nuclear physics)
Robustness (mathematics)
Universe
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Summary:Neutrino physics in the early Universe is key to our understanding of later cosmological stages, such as primordial nucleosynthesis (BBN) or the formation of large-scale structures. The coming decade promises new experimental results to explore and constrain cosmological models even more precisely - which requires robust theoretical predictions. This PhD thesis presents a study of the evolution of neutrinos in the first seconds after the Big Bang, more precisely when the temperature of the Universe is of the order of one mega-electronvolt. This evolution is obtained numerically by solving kinetic equations for which we propose a new derivation. A first application is the calculation of the so-called "standard" decoupling in order to calculate the cosmological parameter quantifying the energy density of the primordial relativistic species, \(N_\mathrm{eff}\), to a precision of a few ten-thousandths. This study has highlighted the possibility of effectively describing the phenomenon of flavour oscillations, taking advantage of the large separation of time scales involved. Such an approximation is then adapted and validated in the case of non-zero asymmetries between neutrinos and antineutrinos. Finally, we study semi-analytically the consequences of incomplete neutrino decoupling on BBN, in order to understand how the primordial abundances of helium and deuterium are affected by this physics.
ISSN:2331-8422