Loop effects in direct detection

Abstract

We consider loop level contributions to dark matter - nucleon scattering in cases where the spin independent scattering cross section is absent or suppressed at tree level. In the case of a pseudoscalar interaction, for which the tree level cross section is both spin-dependent and suppressed by 4 powers of the exchanged momentum, loop diagrams give rise to a non-zero spin independent cross section. We show that if the pseudoscalar interaction is formulated using a gauge invariant framework, loop effects generate an effective χ h vertex and result in a scattering cross section that is within reach of current or forthcoming experiments. We also consider the case of inelastic dark matter, for w..