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Item Fermion mass hierarchy and phenomenology in the 5D Domain Wall Standard Model(2019) Okada, Nobuchika; Raut, Digesh; Villalba, Desmond; University of Alabama TuscaloosaShow more We have recently proposed a setup of the “Domain-Wall Standard Model” in 5D spacetime, where all the Standard Model (SM) fields are localized in certain domains of the extra 5th dimension. Utilizing this setup, we attempt to solve the fermion mass hierarchy problem of the SM. The mass hierarchy can be naturally explained by suitably distributing the fermions in different positions along the extra dimension. Due to these different localization points, the effective 4D gauge couplings of Kaluza-Klein (KK) mode gauge bosons to the SM fermions become non-universal. As a result, our model is severely constrained by the Flavor Changing Neutral Current (FCNC) measurements. We find two interesting cases in which our model is phenomenologically viable: (1) the KK-mode of the SM gauge bosons are extremely heavy and unlikely to be produced at the Large Hadron Collider (LHC), while future FCNC measurements can reveal the existence of these heavy modes. (2) the width of the localized SM fermions is very narrow, leading to almost universal 4D KK-mode gauge couplings. In this case, the FCNC constraints can be easily avoided even if a KK gauge boson mass lies at the TeV scale. Such a light KK gauge boson can be searched at the LHC in the near future.Show more Item Higgs-Portal and Z'-Portal Dark Matters in Brane-World Cosmologies(University of Alabama Libraries, 2023) Liu, Taoli; Okada, NobuchikaShow more According to various astrophysical and cosmological observations, Dark Matter (DM) accounts for approximately 27% of the Universe's total energy density. However, no viable DM particle candidate exists within the framework of the Standard Model (SM) of particle physics. An electrically neutral, weakly interacting massive particle (WIMP) from physics beyond theSM emerges as an appealing candidate for DM. In this dissertation research, we consider the WIMP DM model within the framework of 5-dimensional brane-world cosmology. In this setup, our familiar 3-dimensional space is realized as a hyper-surface embedded in a 4-dimensional space. Within this context, all SM and DM fields are confined to the hyper-surface, while the graviton resides in the bulk. We explore two well-established brane-world cosmologies: the Randall-Sundrum (RS) and the Gauss-Bonnet (GB)brane-world cosmologies. These models reproduce the standard Big Bang cosmology at temperatures below the so-called "transition temperature." However, at higher temperatures, they introduce significant modifications to the universe's expansion dynamics. This non-standard expansion law directly influences the predictions related to WIMP DM physics.In our investigation, we consider two well-founded WIMP DM models: the Higgs-portal scalar DM model and the Z′-portal DM model. We analyze the effects of brane-world cosmology and identify the allowed parameter space by incorporating constraints from the observed DM relic density, as well as data from direct and indirect DM detection experiments. It is worth noting that for both DM models, the allowed parameter regions are severely restricted within the conventional Big Bang cosmological framework. Our findings reveal that these allowed parameter regions face even more stringent limitations in the RS cosmology, and in some cases, they may even disappear entirely. Conversely, the GB cosmological effects significantly expand the regions of parameter space that are allowed. Furthermore, the discovery of Higgs-portal or Z′-portal DM within the GB brane-worldcosmology would enable us to determine the transition temperature.Show more Item Nonlocal non-Abelian gauge theory: Conformal invariance and beta-function(American Physical Society, 2021) Ghoshal, Anish; Mazumdar, Anupam; Okada, Nobuchika; Villalba, Desmond; Istituto Nazionale di Fisica Nucleare (INFN); University of Groningen; University of Alabama TuscaloosaShow more This paper focuses on extending our previous discussion of an Abelian U(1) gauge theory involving infinite derivatives to a non-Abelian SU(N) case. The renormalization group equation (RGEs) of the SU(N) gauge coupling is calculated and shown to reproduce the local theory \(\beta \)-function in the limit of the nonlocal scale \(M\to \infty \). Interestingly, the gauge coupling stops its running beyond the scale \(M\), approaching an asymptotically conformal theory.Show more Item Stability of infinite derivative Abelian Higgs models(American Physical Society, 2018) Ghoshal, Anish; Mazumdar, Anupam; Okada, Nobuchika; Villalba, Desmond; Istituto Nazionale di Fisica Nucleare (INFN); Roma Tre University; University of Groningen; University of Alabama TuscaloosaShow more Motivated by the stringy effects by modifying the local kinetic term of an Abelian Higgs field by the Gaussian kinetic term, we show that the Higgs field does not possess any instability; the Yukawa coupling between the scalar and the fermion, the gauge coupling, and the self interaction of the Higgs yields exponentially suppressed running at high energies, showing that such class of theory never suffers from vacuum instability. We briefly discuss its implications for the early Universe cosmology.Show more Item A tale of two standard model extensions(University of Alabama Libraries, 2019) Villalba, Desmond; Okada, Nobuchika; University of Alabama TuscaloosaShow more The Standard Model (SM) has provided physicists with a nearly complete effective description of the fundamental building blocks for the Universe. While several questions regarding the makeup of our Universe have been resolved, many still remain. One such question deals with the vast energy difference between the electroweak scale and Planck scale (${\cal O}(10^{17}\, {\rm GeV})$). The origin of this large divide has physical implications affecting the running of the Higgs mass, as it receives quantum corrections that are quadratic. Affiliated with this large division of energy scales is an issue that came about upon detection of the Higgs boson at the Large Hadron Collider (LHC), which enabled us to infer the value of the Higgs self-coupling. As a result, the renormalization group equation for the Higgs self-coupling predicts a negative self-coupling at around energies of $10^9 - 10^{11} $ GeV. If true, this would indicate that our vacuum state is unstable. Taking our motivation from stringy effects by modifying the local kinetic term of an Abelian Higgs field by the Gaussian kinetic term, we show that the Higgs field does not possess any instability, and the beta-function of the self-interaction for the Higgs becomes exponentially suppressed at high energies, showing that such class of theory never suffers from a vacuum instability. Another interesting question to consider, is what might be the origin of the large mass difference between the fundamental fermions? As will be shown, the fermion mass hierarchy can be explained through the use of our formalism developed in our setup of the "Domain-Wall Standard Model in a non-compact 5-dimensional space-time", where all the SM fields are localized in certain domains of the 5th dimension. Reproducing the hierarchy is contingent upon the localization positions of the fermions along the extra flat dimension. As a result of these different localization points, the effective 4-dimensional Kaluza-Klein mode gauge couplings become non-universal. This allows for the possibility of interesting experimental considerations which will be discussed. Flavor Changing Neutral Current constraints provide stringent bounds on our model, through these constraints we can glean information about the extra dimension. We have found two possibilities that satisfy these constraints: (1) the KK mode of the SM gauge bosons are extremely heavy and unlikely to be produced at the LHC, however future FCNC measurements can reveal the existence of these heavy modes. (2) the width of the localized SM fermions is very narrow, meaning the 4D KK mode gauge couplings are almost universal. In this case the FCNC constraints can be easily avoided, even for a KK gauge boson mass of order TeV. Such a light KK gauge boson can be discovered at the LHC in the near future.Show more