Searching for Physics Beyond the Standard Model: From Neutrinos to the Higgs Bosons 

Abstract: This thesis is in the field of particle physics phenomenology. It consists of several projects in two major directions: (1) search for new physics effects on Higgs couplings at high energy scales; (2) realization of a UV-complete model of neutrino mass and non-standard interactions, accompanied by the studies of its phenomenological signatures at hadron colliders.

In the search of the “Beyond the Standard Model” (BSM) effects on Higgs couplings, we first explore the new physics reach for the off-shell Higgs boson (h) measurement in the pp -> h^* -> Z(l^+ l^-) Z(\nu \nu_bar) channel at the high-luminosity (HL) LHC. The new physics sensitivity is parametrized in terms of the Higgs boson width, dimension-6 operators in the effective field theory framework, and a non-local Higgs-top coupling form factor. In another project along the same direction, we explore the sensitivity to new physics for the coupling of the Higgs boson and top quark at high energy scales with the process pp -> t t_bar h at the HL-LHC. This process probes the coupling in both the space-like and time-like domains at a high scale, complementary to the off-shell Higgs processes in the time-like domain. Both channels provide strong sensitivity to new physics scale, and they are being studied at current LHC experiments.

In the aspect of BSM effects on neutrino physics, we study the non-standard interactions of neutrinos with light leptonic scalars (\phi) in a global B-L-conserved ultraviolet (UV) complete model. The model utilizes Type-II seesaw motivated neutrino interactions with an SU(2)_L triplet scalar, along with an additional singlet in the scalar sector. This UV- completion leads to an enriched spectrum and consequently new observable signatures. We examine the low-energy lepton flavor violation constraints, as well as the perturbativity and unitarity constraints on the model parameters. Then we lay out a search strategy for the unique signature of the model resulting from the leptonic scalars at the hadron colliders.