One Bump or Two Peaks? The 750 GeV Diphoton Excess and Dark Matter with a Complex Mediator

TL;DR

This paper explores a model with two narrow scalars around 750 GeV to explain the diphoton excess, linking it to dark matter without needing invisible decay modes, and examines experimental constraints on their widths.

Contribution

It proposes a two-scalar model for the 750 GeV excess that connects to dark matter, avoiding the need for large invisible decay widths and addressing experimental constraints.

Findings

Two scalars can explain the diphoton excess without large invisible widths.

The model alleviates tension between collider signals and dark matter constraints.

Possible scalar widths are compatible with current experimental bounds.

Abstract

We consider the possibility that the recently observed excess in the diphoton invariant mass spectrum around 750 GeV is due to two narrow scalars. We demonstrate that there is no need to introduce invisible decay modes to enlarge the widths as long as the two scalars exhibit an appropriate mass splitting. Nevertheless we investigate the possible connection of these two scalars to the dark matter in a toy model with a Majorana fermionic dark matter candidate. We explore how large the widths of the two scalar widths could be taking into account various constraints from collider and dark matter experiments. Introducing two scalars alleviates the tension between the diphoton production and dark matter constraints.