Continuum photon spectrum from Z^1 Z^1 annihilations in universal extra dimensions

TL;DR

This paper calculates the photon spectrum from Z^1 LKP annihilations in universal extra dimensions, showing the continuum flux is small, which enhances the detectability of a sharp gamma-ray line as a dark matter signature.

Contribution

It provides the first detailed calculation of the continuum photon spectrum from Z^1 LKP annihilations, highlighting its implications for dark matter detection strategies.

Findings

Continuum photon flux is relatively small compared to B^1 LKP case.

Spectral endpoint contributions are not large enough to obscure the gamma-ray line.

The small continuum flux enhances the prospects of detecting a sharp gamma-ray line as a dark matter signal.

Abstract

We calculate the continuum photon spectrum from the pair annihilation of a Z^1 LKP in non-minimal universal extra dimensions. We find that, due to the preferred annihilation into W^+ W^- pairs, the continuum flux of collinear photons is relatively small compared to the standard case of the B1 as the LKP. This conclusion applies in particular to the spectral endpoint, where also the additional fermionic contributions are not large enough to increase the flux significantly. When searching for the line signal originating from Z^1 Z^1 annihilations, this is actually a perfect situation, since the continuum signal can be regarded as background to the smoking gun signature of a peak in the photon flux at an energy that is nearly equal to the mass of the dark matter particle. This signal, in combination with (probably) a non-observation of the continuum signal at lower photon energies, constitutes a perfect handle to probe the hypothesis of the Z1 LKP being the dominant component of the dark matter observed in the Universe.