A megaxion at 750 GeV as a first hint of low scale string theory

A bstract 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 suggest 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.