Fermionic dark matter with pseudo-scalar Yukawa interaction

TL;DR

This paper explores a minimal extension of the standard model where fermionic dark matter interacts with a pseudo-scalar, leading to spontaneous CP violation and potential explanations for gamma-ray excesses observed in the galaxy.

Contribution

It introduces a renormalizable model with a pseudo-scalar Yukawa interaction that accounts for dark matter relic density and gamma-ray excesses, constrained by Higgs data.

Findings

Identifies viable parameter space consistent with relic abundance and Higgs decay constraints.

Finds a dark matter candidate around 38 GeV explaining the Fermi-LAT gamma-ray excess.

Demonstrates spontaneous CP violation via pseudo-scalar vacuum expectation value.

Abstract

We consider a renormalizable extension of the standard model whose fermionic dark matter (DM) candidate interacts with a real singlet pseudo-scalar via a pseudo-scalar Yukawa term while we assume that the full Lagrangian is CP-conserved in the classical level. When the pseudo-scalar boson develops a non-zero vacuum expectation value, spontaneous CP-violation occurs and this provides a CP-violated interaction of the dark sector with the SM particles through mixing between the Higgs-like boson and the SM-like Higgs boson. This scenario suggests a minimal number of free parameters. Focusing mainly on the indirect detection observables, we calculate the dark matter annihilation cross section and then compute the DM relic density in the range up to $m_{\text{DM}} = 300$ GeV. We then find viable regions in the parameter space constrained by the observed DM relic abundance as well as invisible Higgs decay width in the light of 125 GeV Higgs discovery at the LHC. We find that within the constrained region of the parameter space, there exists a model with dark matter mass $m_{\text{DM}} \sim 38$ GeV annihilating predominantly into $b$ quarks, which can explain the Fermi-LAT galactic gamma-ray excess.