Title: Phenomenological study of a neutrinophilic U(1) model
Speaker: Mr. Anjan Barik (Harish-Chandra Res. Inst.)
Abstract: In a general U(1) gauge extension of SM where SM fermions are charged under the new abelian gauge group due to the stringent collider bound on the dilepton decay channel of the new gauge boson the strength of new abelian gauge coupling becomes unnaturally small such as in the U(1)B−L model. Therefore, we consider a U(1) extension of the standard model (SM) where the newly added SM singlet neutral vector-like fermions, an additional SM SU (2) doublet scalar, and a singlet scalar are only charged under the new gauge group. These two scalars are responsible for the breaking of the gauged U(1) spontaneously, leading to a light neutral gauge boson (Z′) which has minimal interaction with the SM sector. The neutral fermions couple to the SM leptons through Yukawa interactions. The SM neutrinos in this model become massive via a standard inverse-seesaw mechanism. We study the collider phenomenology of neutrinophilic Z′ in the presence of gauge kinetic mixing (GKM) with the SM hypercharge U(1) gauge group. We found the current experimental limit allows such light new force carrier in the mass range of 200–500 GeV where multilepton channels such as (4ℓ + /ET ) and (3ℓ + 2j + /ET ) will be very effective for its discovery.
When the new force mediator (Z′) is lighter than the Standard Model (SM) gauge bosons to evade all the bounds a smaller value of GKM is required therefore cannot be produced significantly from SM fermions. We highlight a way of discovering such a symmetry at the Large Hadron Collider (LHC) by incorporating scalar mixing which includes the Higgs resonance with four lepton final states. In addition, the hidden sector can induce lepton flavor violating decay of new gauge boson which can become a significant channel for its discovery.
We study dark matter aspects in this neutrinophilic U(1) model. The lightest sterile neutrino in this model can act as a dark matter candidate, especially when its Yukawa coupling with SM leptons and the second Higgs doublet is very small so that its lifetime becomes larger than the age of the universe. In different limits of the parameters, this dark matter candidate can be accommodated in the Weakly Interacting Massive Particle (WIMP) or Feebly Interacting Massive Particle (FIMP) scenarios. In the WIMP case, the observed DM relic density is achieved via the new gauge boson and singlet scalar portal, whereas in the FIMP scenario, these two particles play a crucial role in obtaining observed DM relics.