  In this paper we investigate the direct detections of Majorana dark matter
(MDM) in vector portal. Taking into account that the tree-level scattering
cross sections in these models are either dark matter velocity suppressed or
spin-dependent, we calculate radiative corrections to the spin-independent
cross section in effective field theory approach. Wilson coefficients of
effective MDM-quark interactions are calculated at the one-loop level, and the
Wilson coefficient of the effective MDM-gluon interaction is derived at the
two-loop level. Numerical results show that current constraints can rule out a
narrow mass range of MDM when tree-level contributions are considered, and the
spin-independent cross section from radiative corrections is reachable by the
current direct detection technique for light MDM.
