Electroweak Vacuum Stability and Diphoton Excess at 750 GeV

TL;DR

This paper explores a model where a new scalar particle explains the 750 GeV diphoton excess observed at the LHC, while also examining how this affects the stability of the electroweak vacuum, revealing conflicting constraints.

Contribution

It introduces a simple extension of the Standard Model with a singlet scalar and vector-like fermion to explain the diphoton excess and analyzes the impact on vacuum stability.

Findings

The diphoton excess can be explained by a singlet scalar with a vector-like fermion.

Vacuum stability constraints limit the Yukawa coupling of the fermion and scalar quartic couplings.

Simultaneously explaining the excess and vacuum stability is not feasible in this model.

Abstract

Recently, both ATLAS and CMS collaborations at the CERN Large Hadron Collider (LHC) have announced their observations of an excess of diphoton events around the invariant mass of $750~{\rm GeV}$ with a local significance of $3.6\sigma$ and $2.6\sigma$, respectively. In this paper, we interpret the diphoton excess as the on-shell production of a real singlet scalar in the $pp \to S \to \gamma \gamma$ channel. To accommodate the observed production rate, we further introduce a vector-like fermion $F$, which is carrying both color and electric charges. The viable regions of model parameters are explored for this simple extension of the Standard Model (SM). Moreover, we revisit the problem of electroweak vacuum stability in the same scenario, and find that the requirement for the electroweak vacuum stability up to high energy scales imposes serious constraints on the Yukawa coupling of the vector-like fermion and the quartic couplings of the SM Higgs boson and the new singlet scalar. Consequently, a successful explanation for the diphoton excess and the absolute stability of electroweak vacuum cannot be achieved simultaneously in this economical setup.