Pseudo-Dirac Dark Matter Leaves a Trace

Abstract

Pseudo-Dirac Dark Matter is a viable type of dark matter which originates from a new Dirac fermion whose two Weyl states get slightly split in mass by a small Majorana term. The decay of the heavier to the lighter state naturally occurs over a detectable length scale. Thus, whenever pseudo-Dirac Dark Matter is produced in a collider, it leaves a clear trace: a visible displaced vertex in association with missing energy. Moreover, pseudo-Dirac Dark Matter behaves Dirac-like for relic abundance and Majorana-like in direct detection experiments: it has efficient s-wave annihilations but it lacks of dangerous vector interactions with the quarks in the nuclei. We provide a general treatment using an effective field theory approach, then specializing to the supersymmetric situation of a pseudo-Dirac Bino. The dark matter mass and the mass splitting can be extracted from measurements of the decay length and the invariant mass of the products, even in presence of missing energy.