Effects of dark sector interactions on active-sterile neutrino mixing
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- Master theses 
This thesis presents methods and theory for exploring new physics by using neutrinos as the portal. A thorough introduction on the state of neutrino physics in, and beyond the Standard Model framework, is presented. Anomalies arise from short baseline neutrino oscillation experiments, which may hint towards a fourth neutrino with a mass at the eV-scale. This is explained by the addition of a dark, Abelian symmetry group. The new symmetry is broken at the MeV-scale. To obtain sizeable active-sterile mixing, a hierarchy between Yukawa couplings is required. Majorana masses are included for righthanded neutrinos, which by the see-saw mechanism, provide a spectrum of light neutrino masses. The dark sector neutrinos are allowed to couple to the active neutrinos by Yukawa couplings which form a non-diagonal Yukawa matrix. The interplay between neutrino masses, Yukawa couplings, mixing angles and vacuum expectation values, is studied to provide solutions for the short baseline anomalies while remaining within experimental limits. Simple parameter scans are employed to further investigate the structure of the model. A parameter region compatible with global fits of reactor neutrino data is presented. When applied to bounds arising from resonant leptogenesis, the model confines right-handed neutrino masses in the 1TeV-100TeV range.
Revised version. Minor spelling errors corrected.