A global fit of the $\gamma$-ray galactic center excess within the scalar singlet Higgs portal model

TL;DR

This paper investigates whether the scalar singlet Higgs portal model can explain the gamma-ray excess at the galactic center, considering astrophysical uncertainties and multiple experimental constraints, identifying two viable parameter regions.

Contribution

It provides a comprehensive global fit of the scalar singlet Higgs portal model to the galactic gamma-ray excess, including astrophysical uncertainties and various experimental constraints.

Findings

Two viable parameter regions identified near the Higgs resonance.

One region requires an additional dark matter component beyond the scalar WIMP.

Both regions are challenging to probe with future experiments.

Abstract

We analyse the excess in the $\gamma$-ray emission from the center of our galaxy observed by Fermi-LAT in terms of dark matter annihilation within the scalar Higgs portal model. In particular, we include the astrophysical uncertainties from the dark matter distribution and allow for unspecified additional dark matter components. We demonstrate through a detailed numerical fit that the strength and shape of the $\gamma$-ray spectrum can indeed be described by the model in various regions of dark matter masses and couplings. Constraints from invisible Higgs decays, direct dark matter searches, indirect searches in dwarf galaxies and for $\gamma$-ray lines, and constraints from the dark matter relic density reduce the parameter space to dark matter masses near the Higgs resonance. We find two viable regions: one where the Higgs-dark matter coupling is of ${\cal O}(10^{-2})$, and an additional dark matter component beyond the scalar WIMP of our model is preferred, and one region where the Higgs-dark matter coupling may be significantly smaller, but where the scalar WIMP constitutes a significant fraction or even all of dark matter. Both viable regions are hard to probe in future direct detection and collider experiments.