Wenjie Huang Dissertation Defense

Thesis Title: Searching for New Physics: From Experimental Strategies to Model Building Abstract: This dissertation aims to address some remaining questions that cannot be explained solely with the Standard Model of particle physics. The investigations proceed along two fronts: 1) the development of novel phenomenological frameworks for new physics searches at energy and intensity frontiers that will enhance and broaden the impact of experimental analyses, and 2) the construction of experimentally testable models to explain puzzles like origin of the neutrino mass and the electroweak hierarchy problem. In the first direction, in order to optimize new physics searches at experiments, we study and formulate simplified frameworks in which the new physics signatures are characterized by variables most directly controlling signal event rates and kinematics in the context of long-lived particles that decay inside a neutrino detector. We demonstrate that the use of these simplified frameworks can not only allow for individual experimental analyses to be applicable to a wide variety of specific model scenarios but also serve as a bridge to model identification in the hopeful detection of a new physics signal. In the second direction, we develop theoretical formalism, construct extensions of the Standard Model, and explore their associated phenomenology in the cases of axion mixing with neutral pion in radiation bath, neutrino mass from the electroweak scale, and generalization of the N -Naturalness solution to the electroweak hierarchy problem.