The LHC di-photon excess and Gauge Coupling Unification in Extra $Z^\prime$ Heterotic-String Derived Models

TL;DR

This paper explains the LHC di-photon excess using a heterotic-string derived model with a light $Z'$ and vector-like states, showing compatibility with gauge coupling data and potential for a viable scalar spectrum.

Contribution

It demonstrates that a string-inspired model with a light $Z'$ can account for the di-photon excess while maintaining gauge coupling unification and explores the implications for the supersymmetric spectrum.

Findings

The model explains the di-photon excess via a Standard Model singlet.

Gauge coupling unification is preserved despite additional states.

Heavy thresholds may push supersymmetric particles beyond LHC reach.

Abstract

The di-photon excess observed at the LHC can be explained as a Standard Model singlet that is produced and decays by heavy vector-like colour triplets and electroweak doublets in one-loop diagrams. The characteristics of the required spectrum are well motivated in heterotic-string constructions that allow for a light $Z^\prime$. Anomaly cancellation of the $U(1)_{Z^\prime}$ symmetry requires the existence of the Standard Model singlet and vector-like states in the vicinity of the $U(1)_{Z^\prime}$ breaking scale. In this paper we show that the agreement with the gauge coupling data at one-loop is identical to the case of the Minimal Supersymmetric Standard Model, owing to cancellations between the additional states. We further show that effects arising from heavy thresholds may push the supersymmetric spectrum beyond the reach of the LHC, while maintaining the agreement with the gauge coupling data. We show that the string inspired model can indeed account for the observed signal and discuss the feasibility of obtaining viable scalar mass spectrum.