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Dissertation zugänglich unter
URN: urn:nbn:de:gbv:18-66932
URL: http://ediss.sub.uni-hamburg.de/volltexte/2014/6693/

Neutrino Flavor Conversions in High-Density Astrophysical andCosmological Environments

Umwandlungen der Neutrinoflavors in astrophysikalischen undkosmologischen Umgebungen hoher Dichte

Saviano, Ninetta

 Dokument 1.pdf (3.794 KB) 

Freie Schlagwörter (Deutsch): Neutrino , Kosmologie , Astrophysik
Freie Schlagwörter (Englisch): Neutrino , Cosmology , Astrophysics
Basisklassifikation: 33.10 , 33.50
Institut: Physik
DDC-Sachgruppe: Physik
Dokumentart: Dissertation
Hauptberichter: Mirizzi, Alessandro (Jun. Prof.)
Sprache: Englisch
Tag der mündlichen Prüfung: 19.06.2013
Erstellungsjahr: 2013
Publikationsdatum: 04.04.2014
Kurzfassung auf Englisch: The topic of this thesis is the study of the neutrino flavor conversions in high-density environments: the supernovae and
the the Early Universe. Remarkably, these represent the only two cases in
which neutrinos themselves contribute to the \"background medium\" for their propagation,
making their oscillations a non-linear phenomenon.
In particular, in the dense supernova core, the neutrino-neutrino interactions can lead in some situations to surprising
and counterintuitive collective phenomena, when the entire neutrino system oscillates coherently as a single collective mode.
In this context, we have shown that during the early SN accretion phase (post-bounce times $<$ 0.5 s) the matter density
is so high to dominate over the neutrino density, suppressing the collective flavor conversions.
We have characterized this suppression numerically solving the neutrino propagation equations. We have also supported our finding
with a stability analysis of the neutrino equations of motion.
Neutrino flavor conversions in the Early Universe are another fascinating problem involving collisional damping,
refractive effects from charged leptons and neutrino self-interactions.
In this thesis, we have studied the flavor conversions of active-sterile system of neutrinos in
the Early Universe. This study has been motivated by hints for low-mass sterile neutrinos,
coming from precision cosmological measurements and laboratory oscillation experiments.
We performed an accurate solution of the kinetic equations for the evolution of the active-sterile ensemble
in order to determine the relic abundance of sterile neutrinos. We took into account a possible
primordial neutrino asymmetry $(L > 10^{-3})$ in order to suppress the sterile neutrino production and to find a better
agreement between the cosmological and laboratory hints. Finally, we discuss the implications of our results on
Big-Bang Nucleosynthesis and on the Cosmic Microwave Background from data measured by the Planck experiment.


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