The gamma-ray spectral feature from Kaluza-Klein dark matter annihilation and its observability

TL;DR

This paper explores the potential to detect gamma-ray spectral features from Kaluza-Klein dark matter annihilation, assessing observability with upcoming detectors and setting constraints based on HESS data.

Contribution

It provides a detailed calculation of the gamma-ray spectrum from Kaluza-Klein dark matter and evaluates its detectability, establishing constraints on the boost factor using current observational data.

Findings

Upper limit on boost factor ranges from 1 to 30.

Gamma-ray spectral peak around LKP mass could be observable with future detectors.

Current data do not conclusively detect LKP signals, but future missions may clarify their existence.

Abstract

The theory of universal extra dimensions involves Kaluza-Klein (KK) particles. The lightest KK particle (LKP) is one of the good candidates for cold dark matter. Annihilation of LKP dark matter in the Galactic halo produces high-energy gamma-rays. The gamma-ray spectrum shows a characteristic peak structure around the LKP mass. This paper investigates the observability of this peak structure by near-future detectors taking account of their energy resolution, and calculates the expected energy spectrum of the gamma-ray signal. Then, by using the HESS data, we set some constraints on the boost factor, which is a product of the annihilation cross section relative to the thermal one and an uncertain factor dependent on the substructure of the LKP distribution in the Galactic halo, for each LKP mass. The resulting upper limit on the boost factor is in the range from 1 to 30. The constraints can be regarded as comparable with the results of previous work for gamma-ray and electron-positron observation. However, the observational data for the TeV or higher energy region are still limited, and the possible LKP signal is not conclusive. Thus, we expect near-future missions with better sensitivity will clarify whether the LKP dark matter should exist or not.