Date of Award
8-2023
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
The Standard Model (SM) of Particle Physics has been remarkably successful in explaining the fundamental forces and classifying elementary particles. However, there are various experimental and theoretical indications that suggest the need to go beyond the SM (BSM) and expand our understanding of the fundamental nature of the universe. From a theoretical perspective, there are several limitations of the SM that suggest the existence of a more fundamental theory. For example, the SM does not incorporate gravity, and it fails to explain the hierarchy problem. Additionally, the nature of dark matter and the origin of the mass hierarchy of elementary particles remain unanswered questions. To address these issues, numerous theoretical frameworks and models have been proposed as extensions of the SM, such as Supersymmetry (SUSY), Left-Right Symmetric Model (LRSM), and Extra Dimensions, etc. The BSM theories aim to provide explanations for the observed phenomena beyond the capabilities of the SM and offer new insights into the fundamental nature of the universe. The main motivation behind this dissertation stems from the intriguing experimental results that have hinted at the possibility of Lepton Flavor Violation (LFV) and/or Lepton Flavor Universality Violation (LFUV). These experimental observations deviate from the predictions of the Standard Model of Particle Physics, which assumes strict conservation of lepton flavors and lepton flavor universality. In the first project, we address two types of intriguing phenomena that suggest the violation of Lepton Flavor Universality (LFU) within the framework of R-parity violating Supersymmetry (RPV SUSY). Firstly, we investigate the persistent indications of LFU violation in semileptonic decays of ��-mesons, where experimental measurements deviate from the predictions of the Standard Model. Secondly, we focus on the long-standing discrepancy between the SM prediction and experimental measurements of the muon anomalous magnetic moment, which also suggests LFU violation. By employing the RPV SUSY framework, we propose theoretical solutions to reconcile these deviations between theory and experiment, aiming to reveal the underlying physics responsible for these anomalies. Thirdly, through our extensive numerical scan of the parameter space, we have identified a notable characteristic in our scenarios, namely the orthogonality between the parameter space of the sbottom and the parameter space of the sneutrino. This feature highlights the distinct nature of our proposed scenarios. Finally, we present two unique signals that can serve as potential tests at the LHC, enabling the exploration of the sbottom and sneutrino parameter spaces in our scenarios. In the second project, building upon the insights gained from the first project regarding the orthogonality between the sbottom parameter space and the sneutrino parameter space in the sense that the sbottom plays a crucial role in addressing the ��-physics anomalies, while the sneutrino primarily addresses the muon (�� − 2) anomaly, we specifically concentrate on the muon (�� − 2) anomaly. Again, within the RPV SUSY framework, we propose an alternative solution to address this discrepancy between theory and experiment. Furthermore, we propose and analyze distinctive signals that can be experimentally tested at the LHC, providing evidence for validating our proposed scenarios. In certain scenarios, neutrino Non-Standard Interactions (NSI) can be induced from and interconnected with Lepton Flavor Violation. In the third project, we specifically concentrate on the ������ interactions in the framework of R-Parity Violating Supersymmetry. We consider various cases where different couplings, both Lepton Flavor Violating and Lepton Flavor Conserving, are non-zero. By investigating these cases, we provide a comprehensive analysis of the NSI parameters that can be contributed by ������ interaction terms under different conditions. This study shows the relationship between LFV and NSI within the context of RPV SUSY, offering valuable insights into the interplay between these phenomena. In the fourth project, inspired by the Left-Right Symmetric Model, our project delves into the phenomenology of leptophilic new scalars. Specifically, we investigate the behavior and characteristics of electrically neutral and doubly-charged scalars at high-energy ��+��− colliders, such as the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). We consider both lepton flavor violating (LFV) and lepton flavor conserving (LFC) couplings. We define four distinct configurations representing different combinations of four lepton flavors in the final states in a model-independent manner. By studying multi-lepton final states, including LFV channels, with a center of mass energies ranging from 1 to 3 TeV, we present the sensitivity of the ILC/CLIC experiments in the relevant mass/coupling parameter space and exploit various di-lepton invariant mass distributions to effectively distinguish signal events from background processes.
Language
English (en)
Chair and Committee
Bhupal Dev
Committee Members
Bhupal Dev, Francesc Ferrer, José E. Figueroa-López, Michael C. Ogilvie, Saori Pastore
Recommended Citation
Xu, Fang, "Lepton Flavor Violation and Lepton Flavor Universality Violation: Opportunity for New Physics Beyond the Standard Model" (2023). Arts & Sciences Electronic Theses and Dissertations. 3002.
https://openscholarship.wustl.edu/art_sci_etds/3002