Axion-mediated dark matter and Higgs diphoton signal

TL;DR

This paper explores axion-mediated dark matter models that explain the Fermi gamma ray line, analyze their implications for Higgs diphoton signals, and identify model distinctions based on annihilation and stability constraints.

Contribution

It introduces axion-mediated dark matter models with vector-like leptons, linking gamma ray signals to Higgs diphoton rate modifications and providing constraints from vacuum stability.

Findings

Model with triplet fermion favored for gamma ray line explanation.

Higgs-to-diphoton rate constrained to 1.4-1.5 times the SM value.

Vacuum stability limits the Higgs diphoton enhancement at high cutoff scales.

Abstract

We consider axion-mediated dark matter models motivated by Fermi gamma ray line at 130 GeV, where anomaly interactions of an axion-like scalar mediate a singlet Dirac fermion dark matter (DM) to electroweak gauge bosons. In these models, extra vector-like leptons generate anomaly interactions for the axion and can also couple to the SM Higgs boson to modify the Higgs-to-diphoton rate. We can distinguish models by the branching fraction of the DM annihilation into a photon pair, favoring the model with a triplet fermion. From the condition that the lighter charged extra lepton must be heavier than dark matter for no tree-level DM annihilations, we also show that the ratio of Higgs-to-diphoton rate to the SM value is constrained by vacuum stability to 1.4(1.5) for the cutoff scale of 10(1) TeV.