A Visible QCD Axion from an Enlarged Color Group

TL;DR

This paper proposes a model with an enlarged QCD color group that predicts a visible axion with a mass potentially at the TeV scale, leading to observable signals at the LHC, including possible explanations for the 750 GeV diphoton resonance.

Contribution

It introduces a new framework where an enlarged color group generates a heavy, visible axion with distinctive collider signatures, connecting axion physics with TeV-scale phenomena.

Findings

Predicts a TeV-scale axion with observable decay channels

Links the axion mass to a new confinement scale around TeV

Suggests vector-like quarks and scalar resonances in the multi-TeV range

Abstract

We consider the possibility of an enlarged QCD color group, SU(3+$N^\prime$) spontaneously broken to SU(3)$_c\times$SU($N^\prime$) with extra vector-like quarks transforming in the fundamental representation. When the heavy quarks are integrated out below the PQ-breaking scale, they generate an axion coupling which simultaneously solves the strong CP problem for both gauge groups. However, the axion mass now receives a new nonperturbative contribution from the SU($N^\prime$) confinement scale, which can be substantially larger than the QCD scale. This can increase the axion mass to be at or above the electroweak scale. This visible axion can then decay into gluons and photons giving rise to observable signals at Run-II of the LHC. In particular, if the mass is identified with the 750 GeV diphoton resonance then the new confinement scale is $\sim$ TeV and the PQ-breaking scale is $\sim$ 10 TeV. This predicts vector-like quarks and a PQ scalar resonance in the multi-TeV range, with the possibility that dark matter is an SU($N^\prime$) baryon.