750 GeV diphoton resonance in a visible heavy QCD axion model

TL;DR

This paper explores a heavy QCD axion model where a 750 GeV scalar resonance decays into axions, potentially explaining the diphoton excess observed at the LHC, with implications for axion decay properties and model consistency.

Contribution

It proposes a novel heavy QCD axion model that accounts for the 750 GeV diphoton resonance while maintaining the Peccei-Quinn mechanism and avoiding domain wall issues.

Findings

The 750 GeV resonance is identified as a scalar from PQ symmetry breaking.

Axion decay length and branching ratios can explain the diphoton excess.

Multiple extra fermion sets are compatible without domain wall problems.

Abstract

In this paper, we revisit a visible heavy QCD axion model in light of the recent reports on the $750$ GeV diphoton resonance by the ATLAS and CMS experiments. In this model, the axion is made heavy with the help of the mirror copied sector of the Standard Model while the successful Peccei-Quinn mechanism is kept intact. We identify the $750$ GeV resonance as the scalar boson associated with spontaneous breaking of the Peccei-Quinn symmetry which mainly decays into a pair of the axions. We find that the mixings between the axion and $\eta$ and $\eta'$ play important roles in its decays and the resultant branching ratio into two photons. The axion decay length can be suitable for explaining the diphoton excess by the di-axion production when its decay constant $f_a \simeq 1$ TeV. We also find that our model allows multiple sets of the extra fermions without causing the domain wall problem, which is advantageous to explain the diphoton signal.