Pseudoscalar Decaying Only via Loops as an Explanation for the 750 GeV Diphoton Excess

Measuring the Diphoton Coupling of a 750 GeV Resonance

A slight excess has been observed in the first data of photon-photon events at the 13 TeV Large Hadron Collider that might be interpreted as a hint of physics beyond the standard model. We show that a completely model-independent measurement of the photon-photon coupling of a putative 750 GeV resonance is possible using the forward proton detectors scheduled at ATLAS and CMS.

Footprints of New Strong Dynamics via Anomaly and the 750 GeV Diphoton

The chiral anomaly provides smoking-gun evidence of a new confining gauge theory. Motivated by a reported event excess in a diphoton invariant mass distribution at the LHC, we discuss a scenario that a pseudo-Nambu-Goldstone (PNG) boson of a new QCD-like theory is produced by gluon fusion and decays into a pair of the standard model gauge bosons. Despite the strong dynamics, the production cross section and the decay widths are determined by an anomaly matching condition. The excess can be explained by the PNG boson with mass of around 750 GeV. The model also predicts exotic hadrons such as a color-octet scalar and baryons. Some of them are within the reach of the LHC experiment.

750 GeV Diphoton Excess May Not Imply a 750 GeV Resonance

We discuss nonstandard interpretations of the 750 GeV diphoton excess recently reported by the ATLAS and CMS Collaborations which do not involve a new, relatively broad resonance with a mass near 750 GeV. Instead, we consider the sequential cascade decay of a much heavier, possibly quite narrow, resonance into two photons along with one or more additional particles. The resulting diphoton invariant mass signal is generically rather broad, as suggested by the data. We examine three specific event topologies-the "antler," the "sandwich," and the two-step cascade decay-and show that they all can provide a good fit to the observed published data. In each case, we delineate the preferred mass parameter space selected by the best fit. In spite of the presence of extra particles in the final state, the measured diphoton p_{T} spectrum is moderate due to its anticorrelation with the diphoton invariant mass. We comment on the future prospects of discriminating with higher statistics between our scenarios, as well as from more conventional interpretations.