Gauge higgs unification in extra dimensions and spin-3/2 dark matter

A Thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in ful llment of the requirements for the degree of Doctor of Philosophy. April 2018In this thesis we discuss various gauge group structures in the gauge-Higgs uni - cation models. The rst group we considered was a toy SU(3) model, where it is possible to have the uni cation of gauge and top Yukawa couplings, which is an attractive feature of gauge-Higgs uni cation models in extra-dimensions. This feature is usually considered di cult to obtain based on simple group theory analyses. We reconsider several minimal toy models calculating the renormalisation group running at one loop. Our results show that the gauge couplings unify asymptotically at high energies, and that this may result from the presence of an UV xed point. The Yukawa coupling in our toy models is enhanced at low energies, showing that a genuine uni cation of gauge and Yukawa couplings may be achieved. Furthermore, the evolution of the Cabibbo-Kobayashi-Maskawa matrix elements, the Jarlskog invariant and the quark mixings are derived for the one-loop renormalisation group equations in a ve-dimensional models for an SU(3) gauge group compacti ed on an S1=Z2 orbifold. We have assumed that there is a fermion doublet and two singlets located at the xed points of the extra dimension, which pointed to some interesting phenomenology in this toy model. We then explicitly test in a simpli ed 5-dimensional model with SU(5), SU(5) U(1)0 and G2 gauge symmetries, the evolution of the gauge couplings, by assuming that all the matter elds are propagating in the bulk, and consider orbifolds based on Abelian discrete groups which lead to 5-dimensional gauge theories compacti ed on an S1=Z2. The gauge couplings evolution is derived at one-loop level and used to test the impact on lower energy observables, in particular the Weinberg angle. For our numerical calculations we have assumed that the fundamental scale is not far from the scope of the Large Hadron Collider, where we choose the compacti cation radii to be the following benchmark values: 1TeV, 4TeV, 5TeV, 8TeV, 10TeV, 15TeV and 20TeV. As these gauge-Higgs uni cation models can also contain many additional particles, we sought to use these particles as dark matter (DM) candidates. As many studies have already been done on various spin DM particles, we chose to focus on the more exotic spin-3/2 fermionic DM. We have allowed interactions with standard model fermions through a vector mediator in the s-channel in our rst considerations. An interesting feature of the spin-3/2 nature of the standard model particles is that there exists a minimum value of the DM mass for a given coupling and mediator mass, below which the decay width of the mediator exceeds the mediator mass. We nd that for pure vector couplings almost the entire parameter space in DM and mediator mass is consistent with the observed relic density, and is ruled out by the direct detection observations through DM-nucleon elastic scattering cross-section. In contrast, for pure axial-vector coupling, the most stringent constraints are obtained from mono-jet searches at the Large Hadron Collider. We have also considered a spin-3/2 fermionic DM particle interacting with the standard model quarks through the exchange of a charged and coloured scalar or vector mediator in a simple t-channel model. It is found that for the vector mediator case almost the entire parameter space allowed by the observed relic density is already ruled out by the direct detection LUX data. There are no such bounds which exist on the interaction mediated by scalar particles. Monojet + missing energy searches at the Large Hadron Collider provide the most stringent bounds on the parameters of the model for this case. The collider bounds put a lower limit on the allowed DM masses. These studies have shown a variety of particle phenomenology beyond the standard model, where such models can be constrained from both collider and astrophysical data.MT 201

Minimal Spin-3/2 Dark Matter in a simple ss-channel model

We consider a spin~-~3/2 fermionic dark matter candidate (DM) interacting with Standard Model fermions through a vector mediator in the $s$-channel. We find that for pure vector couplings almost the entire parameter space of the DM and mediator mass consistent with the observed relic density is ruled out by the direct detection observations through DM-nucleon elastic scattering cross-sections. In contrast, for pure axial-vector coupling, the most stringent constraints are obtained from mono-jet searches at the Large Hadron Collider.Comment: 8 pages, 5 figures, Version accepted for publication in EPJ

Spin-3/2 dark matter in a simple tt-channel model

We consider a spin-3/2 fermionic dark matter (DM) particle interacting with the Standard Model quarks through the exchange of a charged and coloured scalar or vector mediator in a simple $t$-channel model. It is found that for the vector mediator case, almost the entire parameter space allowed by the observed relic density is already ruled out by the direct detection LUX data. No such bounds exist on the interaction mediated by scalar particles. Monojet + missing energy searches at the Large Hadron Collider provide the most stringent bounds on the parameters of the model for this case. The collider bounds put a lower limit on the allowed DM masses.Comment: Published EPJC versio

Unification of gauge and Yukawa couplings

The unification of gauge and top Yukawa couplings is an attractive feature of gauge-Higgs unification models in extra-dimensions. This feature is usually considered difficult to obtain based on simple group theory analyses. We reconsider a minimal toy model including the renormalisation group running at one loop. Our results show that the gauge couplings unify asymptotically at high energies, and that this may result from the presence of an UV fixed point. The Yukawa coupling in our toy model is enhanced at low energies, showing that a genuine unification of gauge and Yukawa couplings may be achieved.Comment: 5 pages, 2 figure; new results, extended discussion, conclusions unchange

The scale invariant scotogenic model: CDF-II WW-boson mass and the 95~GeV excesses

The anomalies observed in the $W$ mass measurements at the CDF-II experiments and the excesses seen around 95~GeV at the Large Hadron Collider (LHC) motivate this work, in which we investigate and constrain the parameter space of the Scale Invariant Scotogenic Model with a Majorana dark matter candidate. The scanned parameters are chosen to be consistent with the dark matter relic density and the observed excesses at $\sim95$~GeV signal strength rates in $\gamma\gamma$, $b\bar b$ and $\tau^+\tau^-$ final states. Furthermore, the model's viable parameters can be probed in both the LHC and future $e^+e^-$ colliders for di-Higgs production.Comment: 8 pages, 1 table, 4 figure

Asymptotic Grand Unification: The SO(10) case

We explicitly test the asymptotic grand unification of a minimal 5-dimensional model with SO(10) gauge theory compactified on an $S^{1}/Z_{2}\times Z^{\prime}_{2}$ orbifold. We consider all matter fields as propagating in the bulk and show that the gauge couplings asymptotically run to a fixed point in the UV. However, the Yukawa couplings will typically hit a Landau pole right above the compactification scale in this class of SO(10) models.Comment: 6 pages, 1 figure, submitted to the PACP2022 conference proceeding

SU(5) aGUT: a minimal asymptotic grand unification model

We present a new grand unification paradigm, where gauge couplings do not need to be equal at any given scale, instead they run towards the same fixed point in the deep ultraviolet. We provide a concrete example based on SU(5) with a compactified extra space dimension. By construction, fermions are embedded in different SU(5) bulk fields, hence baryon number is conserved and proton decay is forbidden. The lightest Kaluza-Klein tier consists of stable states, providing an asymmetric Dark Matter candidate via their baryonic charges, with a mass of 2.4 TeV. The model features an interesting and predictive flavour structure.Comment: 6 pages, contribution to the 41st International Conference on High Energy physics - ICHEP2022, 6-13 July, 2022, Bologna, Ital

Evolution of the gauge couplings and Weinberg angle in 5-dimensions for a G2_2 gauge group

International audienceWe explicitly test, in a simplified 5-dimensional model with G (2) gauge symmetry, the evolution of the gauge couplings. We assume that all the matter fields are propagating in the bulk, and consider orbifolds based on Abelian discrete groups which lead to 5-dimensional gauge theories compactified on an S (1)/Z (2). The gauge couplings evolution is derived at one-loop level and used to test the impact on lower energy observables, in particular the Weinberg angle

Evolution of the gauge couplings and Weinberg angle in 5-dimensions for an SU(5) and flipped SU(5) gauge group

International audienceWe explicitly test, in a simplified 5-dimensional model with SU(5) and SU(5) × U(1)′ gauge symmetries, the evolution of the gauge couplings. We assume that all the matter fields are propagating in the bulk, and consider orbifolds based on Abelian discrete groups which lead to 5-dimensional gauge theories compactified on an S (1)/Z (2). The gauge couplings evolution is derived at one-loop level and used to test the impact on lower energy observables, in particular the Weinberg angle