Majorana Fermion Dark Matter in Minimally Extended Left-Right Symmetric Model

Abstract: We present a minimal extension of the left-right symmetric model based on the gauge group $SU(3){c} \times SU(2){L} \times SU(2){R} \times U(1){B-L} \times U(1){X}$, in which a vector-like fermion pair ($\zeta_L$ and $\zeta_R$) charged under the $U(1){B-L} \times U(1)X$ symmetry is introduced. Associated with the symmetry breaking of the gauge group $SU(2){R} \times U(1){B-L} \times U(1){X}$ down to the Standard Model (SM) hypercharge $U(1)Y$, Majorana masses for $\zeta{L, R}$ are generated and the lightest mass eigenstate plays a role of the dark matter (DM) in our universe by its communication with the SM particles through a new neutral gauge boson "$X$". We consider various phenomenological constraints of this DM scenario, such as the observed DM relic density, the LHC Run-2 constraints from the search for a narrow resonance, and the perturbativity of the gauge couplings below the Planck scale. Combining all constraints, we identify the allowed parameter region which turns out to be very narrow. A significant portion of the currently allowed parameter region will be tested by the High-Luminosity LHC experiments.