Displaced Vertices from X-ray Lines

TL;DR

This paper proposes a weak-scale dark matter model with nearly degenerate states that produce X-ray lines through radiative decay, offering observable signatures at colliders and explaining the 3.55 keV line.

Contribution

It introduces a novel dark matter model with specific decay mechanisms and collider signatures, connecting X-ray observations to particle physics.

Findings

The model explains the 3.55 keV X-ray line.

Predicted collider signatures include displaced leptons and jets.

Decay rates are consistent with the X-ray line intensity.

Abstract

We present a simple model of weak-scale thermal dark matter that gives rise to X-ray lines. Dark matter consists of two nearly degenerate states near the weak scale, which are populated thermally in the early universe via co-annihilation with slightly heavier states that are charged under the Standard Model. The X-ray line arises from the decay of the heavier dark matter component into the lighter one via a radiative dipole transition, at a rate that is slow compared to the age of the universe. The model predicts observable signatures at the LHC in the form of exotic events with missing energy and displaced leptons and jets. As an application, we show how this model can explain the recently observed 3.55 keV X-ray line.