A Megaxion at 750 GeV as a First Hint of Low Scale String Theory

TL;DR

This paper proposes that a 750 GeV resonance observed at LHC could be a heavy axion-like particle (megaxion) arising from low scale string theory, with implications for string scale and additional gauge bosons.

Contribution

It introduces a novel interpretation of the 750 GeV resonance as a megaxion from low scale string models, connecting collider signals to string theory parameters.

Findings

The 750 GeV resonance could be a heavy axion-like particle (megaxion).

The string scale is estimated to be around 7-10^4 TeV based on this interpretation.

An extra Z' gauge boson might be detectable before reaching the string threshold.

Abstract

Low scale string models naturally have axion-like pseudoscalars which couple directly to gluons and photons (but not $W$s) at tree level. We show how they typically get tree level masses in the presence of closed string fluxes, consistent with the axion discrete gauge symmetry, in a way akin of the axion monodromy of string inflation and relaxion models. We discuss the possibility that the hints for a resonance at 750 GeV recently reported at ATLAS and CMS could correspond to such a heavy axion state (megaxion). Adjusting the production rate and branching ratios suggests the string scale to be of order $M_s$ ~ $7 - 10^4$ TeV, depending on the compactification geometry. If this interpretation was correct, one extra $Z'$ gauge boson could be produced before reaching the string threshold at LHC and future colliders.