The Fermionic Dark Matter Higgs Portal: an effective field theory approach

Abstract

We consider fermionic (Dirac or Majorana) cold thermal relic dark-matter coupling to standard-model particles through the effective dimension-5 Higgs portal operators ${\Lambda }^{-1}{\mathcal{O}}_{\text{DM}}\cdot H^{†}H$, where ${\mathcal{O}}_{\text{DM}}$ is an admixture of scalar $\bar{\chi }\chi$ and pseudoscalar $\bar{\chi }i{\gamma }_5\chi$ DM operators. Utilizing the relic abundance requirement to fix the couplings, we consider direct detection and invisible Higgs width constraints, and map out the remaining allowed parameter space of dark-matter mass and the admixture of scalar and pseudoscalar couplings. We emphasize a subtlety which has not previously been carefully studied in the context of the EFT approach, in which an effect arising due to electroweak symmetry breaking can cause a naïvely pure pseudoscalar coupling to induce a scalar coupling at higher order, which has important implications for direct detection bounds. We provide some comments on indirect detection bounds and collider searches.

Comments: 22 pages, 8 figures. Published version