## Arts & Sciences Electronic Theses and Dissertations

#### Date of Award

Winter 12-15-2021

#### Author's School

Graduate School of Arts and Sciences

Physics

#### Degree Name

Doctor of Philosophy (PhD)

Dissertation

#### Abstract

The Standard Model (SM) of Particle Physics provides a self-consistent quantum field theoretic framework to explain three of the four known fundamental forces (electromagnetic, weak, strong) along with classifying all known elementary particles. Since its conception in the 1960s, the SM has been one of the most tested theories of physics and has withstood all experimental batterings. In spite of these successes, there are compelling indications, both experimental and theoretical, that require us to expand our understanding of the nature beyond the SM (BSM). Arguably the most glaring indication of BSM physics is the observation of neutrino oscillations, which implies that neutrinos are massive. The underlying BSM physics responsible for neutrino mass must necessarily involve new BSM interactions of neutrinos.In this dissertation, we focus on some case studies of the theory and phenomenology of these new BSM neutrino interactions. On the theoretical side, we consider a class of BSM scenarios for neutrino masses with extra gauge groups, whose generators contribute to the electric charge, and studied the effect of perturbativity constraints on these models, assuming them to be valid up to higher energy scales. In particular, we have derived lower bounds on the new gauge bosons and their couplings from perturbativity considerations, which have important implications for future searches of these BSM particles. In our second work, we have developed analytic techniques to study the vacuum stability and spontaneous symmetry breaking for generic multi-Higgs potential, with application to the well-motivated Left-Right Symmetric Model (LRSM) as an example study. We found that requiring vacuum stability in conjunction with other phenomenological constraints significantly reduces the available parameter space for low-scale LRSM. On a more phenomenological side, we study the effect of Non-standard interactions (NSI) of neutrinos with matter mediated by a scalar field. We develop general techniques to study matter effects and long-range force effects consistently in all media. We show that observable scalar NSI effects, although precluded in terrestrial experiments, are still possible in future solar and supernovae neutrino data, and in cosmological observations such as cosmic microwave background and big bang nucleosynthesis data. In another project, we study the experimental prospects for a scenario with neutrino interactions with right-handed neutrinos $\nu_R$ charged under a hidden $U(1)$ gauge group. We investigate the loop-induced couplings and find that the $\nu_R$-philic dark photon is not inaccessible dark and can be of potential importance to future dark photon searches. In our final project, we explore the production of baryon asymmetry through resonant leptogenesis and phenomenological signatures of the type-I seesaw scenario with a given flavor and CP symmetry group. We find that requiring successful baryon asymmetry generation via resonant leptogenesis imposes interesting constraints for the detection prospects of heavy neutrinos at colliders, as well as in future neutrinoless double beta decay experiments.

English (en)

Soumendra Lahiri

Bhupal Dev

COinS