Subdominant Left-Right Scalar Dark Matter as Origin of the 750 GeV Di-photon Excess at LHC

TL;DR

This paper proposes a left-right symmetric model with scalar septuplets to explain the 750 GeV di-photon excess at LHC, while also providing a subdominant dark matter candidate and discussing additional dark matter possibilities.

Contribution

It introduces a novel scalar septuplet extension to the left-right model that enhances di-photon decay width and links it to dark matter phenomenology.

Findings

Predicts a 36 GeV decay width for the 750 GeV scalar.

Achieves di-photon signal consistent with LHC data.

Dark matter candidates are subdominant and compatible with detection bounds.

Abstract

We study the possibility of explaining the recently reported 750 GeV di-photon excess at LHC within the framework of a left-right symmetric model. The 750 GeV neutral scalar in the model is dominantly an admixture of neutral components of scalar bidoublets with a tiny fraction of neutral scalar triplet. Incorporating $SU(2)$ septuplet scalar pairs into the model, we enhance the partial decay width of the 750 GeV neutral scalar into di-photons through charged septuplet components in loop while keeping the neutral septuplet components as subdominant dark matter candidates. The model also predicts the decay width of the 750 GeV scalar to be around 36 GeV to be either confirmed or ruled out by future LHC data. The requirement of producing the correct di-photon signal automatically keeps the septuplet dark matter abundance subdominant in agreement with bounds from direct and indirect detection experiments. We then briefly discuss different possibilities to account for the remaining dark matter component of the Universe in terms of other particle candidates whose stability arise either due to remnant discrete symmetry after spontaneous breaking of $U(1)_{B-L}$ or due to high $SU(2)$-dimension forbidding their decay into lighter particles.