Theory and phenomenology of the Vector Dark Matter with Fermionic Portal

Thongyoi, Nakorn (2024) Theory and phenomenology of the Vector Dark Matter with Fermionic Portal. University of Southampton, Doctoral Thesis, 171pp.

Record type: Thesis (Doctoral)

Abstract

Even though the Standard Model (SM) of elementary particle physics is very successful in explaining countless microscopic phenomena, it is still not the ultimate theory of everything we have been seeking for. So far we witness several drawbacks of the SM, for example, the neutrino masses, Dark Matter (DM), dark energy, Baryon Asymmetry of the Universe (BAU) and the SM anomalies. Especially, the long standing issue of DM of the universe which has been well-established by multiple cosmological observations and constrained by several ground-based experiments. Additionally, the recent experiment on muon g_μ-2 by the Fermilab National Accelerator Laboratory (FNAL) has precisely measured the anomalous magnetic moment of the muon and implies a 5σ tension between SM prediction and experimental results. In this thesis, we have introduced a new mechanism to connect the SM and dark sector through a fermionic portal. This class of model extends the SM gauge group with a new SU(2)_D ×U(1)_YD^global group while all SM particles are neutral with respect to the additional groups. Two of the new gauge bosons (V_D^(*)) form a complex gauge boson and carry U(1)_YD^global charge. Thus, they can play a role as a DM candidate for this class. Moreover, two generic Vector Like (VL) fermions are introduced to mediate the interaction between the SM and dark sectors equipping us the opportunity to study the DM dark matter phenomenology at collider and non-collider environments. The origin of masses for new degrees of freedom is provided by the interaction with an additional complex scalar doublet (Φ_D) through the spontaneous breakdown of the SU(2)_D ×U(1)_YD^global into U(1)_QD^global when the scalar Φ_D acquires the Vacuum Expectation Value (VEV). The residual symmetry U(1)_QD^global acts as a stabiliser of the DM candidate of the model. The key feature of this model is the Higgs portal to dark sector is not necessarily required but the connection to SM sector is induced by new Yukawa terms between SM and VL fermions, hence the title -- the Vector Dark Mater with Fermionic Portal (FPVDM). The FPVDM model suggests numerous phenomenological implications for collider and non-collider studies. In this thesis, we will discuss only two scenarios from this class: the top quark and muonic portal scenarios, as presented in chapter 3 and 4, respectively. In chapter 3, we discuss in detail a realisation with VL top quark partners (TPVDM), assuming no mixing between the two physical scalars of the theory, the SM Higgs boson and its counterpart in the dark sector. The material presented in this chapter is based on the publications [1,2]. In collider phenomenology point of view, it predicts multiple interesting signatures that a complete set of signatures is presented in table 3.1. These are mono-jet from initial state radiation (ISR) or from loop, ttbar+E_T^miss, 4-top quarks, and the production of hV' and V'V'. The VL Z₂-odd partner t_D could be long-lived and leaves a charged track by decaying into the DM and the SM quarks and/or leptons. In addition, the new gauge boson V' could also be long-lived if its mass is below ttbar threshold and decays into a pair of bbbar via a loop diagram. The cosmological bounds (relic abundance, direct and indirect detection) play a vital role in constraining the parameter space of the model. Especially, the direct detection limit which is absent at tree level. However, at loop level, it leads to a crucial constraint based on the triangle loop of DM-DM-Z/γ. The generic formulas for these triangle loops are present here. In addition, we also explore the possibility to apply the FPVDM framework to explain the muon anomalous magnetic moment or the so-called g_μ-2 and the DM at the same time where we assume the existence of VL muons μ_D and μ'. This scenario is referred to as the MPVDM and will be a topic of chapter 4 which is based on upcoming article entitled ``The muon anomalous magnetic moment g_μ-2 from the Fermionic Portal to Vector Dark Matter" [3]. Like the TPVDM, we are not considering the Higgs portal in this study. The interplay between cosmological and g_μ-2 constraints plays a crucial role in limiting the parameter space of the MPVDM. We found that the allowed region appears on the resonance position of new scalar H_D. Moreover, the collider constraints from LHC data according to pp -> μ⁺μ^-+ E_T^miss searches set up the lower limits on the VL muon masses around 700-800 GeV depending on the parameter space. Several interesting signatures are predicted with 6-10 leptons in the final state. We also provide benchmarks which are allowed by g_μ-2, cosmological and collider constraints for testing the model in future.