Large loop-coupling enhancement of a heavy pseudoscalar from a light dark sector

TL;DR

This paper proposes a model where a heavy pseudoscalar interacts with new vector-like leptons, producing a sharp diphoton resonance through threshold enhancements, and also provides a dark matter candidate consistent with current constraints.

Contribution

It introduces a novel scenario with threshold-enhanced diphoton signals from a heavy pseudoscalar coupled to a dark sector, compatible with experimental limits.

Findings

Achieves a sharp diphoton resonance via loop effects

Provides a dark matter candidate matching observed abundance

Deviates from the Standard Model at 2 sigma level

Abstract

The small background and the sensitivity to charged particles via a leading order loop coupling make the diphoton channel a privileged experimental test for new physics models. We propose a simple archetypal scenario to generate a sharp di-photon resonance as a result of threshold enhancements in the effective coupling between a heavy pseudoscalar particle and new vector-like leptons. We therefore study three different scenarios consistent with the current experimental limits and deviating from the Standard Model at the 2~$\sigma$ level. The model also introduces a natural dark matter candidate able to match the observed dark matter abundance and comfortably respect the current direct detection constraints.