Pseudoscalar mediators: a WIMP model at the neutrino floor

Abstract

Due to its highly suppressed cross section (fermionic) dark matter\ninteracting with the Standard Model via pseudoscalar mediators is expected to\nbe essentially unobservable in direct detection experiments. We consider both a\nsimplified model and a more realistic model based on an extended two Higgs\ndoublet model and compute the leading one-loop contribution to the effective\ndark matter- nucleon interaction. This higher order correction dominates the\nscattering rate completely and can naturally, i.e. for couplings of order one,\nlead to a direct detection cross section in the vicinity of the neutrino floor.\nTaking the observed relic density and constraints from low-energy observables\ninto account we analyze the direct detection prospects in detail and find\nregions of parameter space that are within reach of upcoming direct detection\nexperiments such as XENONnT, LZ, and DARWIN.\n