Indirect Detection Imprint of a CP Violating Dark Sector

TL;DR

This paper proposes a CP-violating dark sector model with fermionic dark matter and scalar mediators that can explain the Galactic Center gamma-ray excess while satisfying detection constraints, and suggests collider tests for the model.

Contribution

It introduces a novel CP-violating scalar mixing scenario that enables dark matter annihilation consistent with gamma-ray observations and detection bounds.

Findings

Model fits gamma-ray spectrum with 60-80 GeV dark matter.

Scalar mixing allows s-wave annihilation into di-scalars.

LHC searches for exotic Higgs decays can test the model.

Abstract

We introduce a simple scenario involving fermionic dark matter ($\chi$) and singlet scalar mediators that may account for the Galactic Center GeV $\gamma$-ray excess while satisfying present direct detection constraints. CP-violation in the scalar potential leads to mixing between the Standard Model Higgs boson and the scalar singlet, resulting in three scalars $h_{1,2,3}$ of indefinite CP-transformation properties. This mixing enables s-wave $\chi{\bar\chi}$ annihilation into di-scalar states, followed by decays into four fermion final states. The observed $\gamma$-ray spectrum can be fitted while respecting present direct detection bounds and Higgs boson properties for $m_{\chi} = 60 \sim 80 $ GeV, and $m_{h_3} \sim m_{\chi}$. Searches for the Higgs exotic decay channel $h_1 \to h_3 h_3$ at the 14 TeV LHC should be able to further probe the parameter region favored by the $\gamma$-ray excess.