Displaced vertices from X-ray lines

Adam Falkowski,Yonit Hochberg,Joshua T Ruderman

doi:10.1007/jhep11(2014)140

Abstract

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.

Highlights

JHEP11(2014)140 dark matter is by no means the unique explanation
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

Summary

Dark matter decays

Thanks to the mixing with the active states, χ1 and χ2 acquire a small coupling to the SM gauge fields. The mass splitting between χ2 and χ1 opens the phase space for the decays χ2 → χ1νν and χ2 → χ1γ The former is a 3-body decay process proceeding at tree-level via an off-shell Z boson. In the interesting parameter space where δ is small, the 3-body decay is completely subdominant to the 2body radiative decay width, which is proportional to δ3. Since in the L-parity limit N1 does not mix with or couple to the dark matter, the dipole operator vanishes. The. 3-body decay vanishes in the L-parity limit due to the vanishing coupling to the Z boson

Relic abundance

Parameter space

LHC phenomenology

General X-ray lines

Summary