Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.......110k&link_type=abstract
Thesis (PhD). HELSINGIN YLIOPISTO (FINLAND), Source DAI-C 61/01, p. 243, Spring 2000, 112 pages.
Astronomy and Astrophysics
Astrophysics
Scientific paper
The objective of this thesis is to study neutrino properties in the framework of astrophysics and cosmology. The research is concentrated on phenomena connected with the active galactic nuclei (AGN) that are supposed to be the origin of highest energy cosmic rays and ultra-high energy neutrinos. The recent SuperKamiokande results on the atmospheric neutrino flux strongly indicate that neutrinos have a mass and that they mix with each other. This discovery has made the study of neutrino properties particularly topical. The observation of very high-energy neutrinos that are supposed to be produced in AGN or related objects would provide a new probe for testing oscillations, electromagnetic properties, decays and beyond-the-SM interaction forms of neutrinos. It is shown that one may obtain stricter constraints on the strength of exotic neutrino-neutrino interactions than the existing limits from laboratory experiments and other astrophysical observations. It is also shown that the observation of AGN neutrino flux may reveal important information about neutrino magnetic moments. The long travelling distance of AGN neutrinos allows for a sensitive test of neutrino instability. The decay of a heavy neutrino into a light neutrino and a scalar is studied, and it is shown that the appropriate coupling strength may be tested in an accuracy several orders of magnitude better than in other phenomena. Also cosmology provides information of the basic neutrino properties. The thermalization of the wrong-helicity Dirac neutrinos is studied by paying attention in particular to the pole effects of the weak gauge bosons. By solving numerically the relevant Boltzmann equation the abundance of wrong-helicity neutrinos is evaluated.
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