The electron plus positron spectrum from annihilation of Kaluza–Klein dark matter in the Galaxy

Abstract

The lightest Kaluza-Klein particle (LKP), which appears in the theory of universal extra dimensions, is one of good candidates for cold dark matter (CDM). When LKP pairs annihilate around the center of the Galaxy where CDM is concentrated, there are some modes which produce electrons and positrons as final products, and we categorize them into two components. One of them is the "Line" component, which directly annihilates into electron-positron pair. Another one is the "Continuum" component, which consists of secondarily produced electrons and positrons via some decay modes. Before reaching Earth, directions of electrons and positrons are randomized by the Galactic magnetic field, and their energies are reduced by energy loss mechanisms. We assume the LKP is in the mass range from 300 GeV to 1500 GeV. We calculate the electron plus positron spectrum after propagation in the Galactic halo to Earth, and we analyze the resulting spectrum and positron fraction. We also point out that the energy dependence of observed positron fraction is well reproduced by the mixture of "line" and "continuum" components. We can fit the electron plus positron spectrum and the positron fraction by assuming appropriate boost factors describing dark matter concentration in the Galactic halo. However, it is difficult to explain both the electron plus positron spectrum and the positron fraction by a single boost factor, if we take account of observational data obtained by AMS-02 only.

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

“…In addition, the relevant value for the boost factor, B f , to explain the total electron plus positron spectrum observed by AMS-02 is given in range from 0 to 240 by assuming specific dark matter halo density model, halo propagation model and m B (1) = 1000 GeV. 35 This constraint can be comparable with our result for analysis of the gamma-ray spectrum.…”

Concentration of Kaluza-Klein dark matter in the Galactic center: constraints from gamma-ray signals

“…The relevant value for the boost factor, B f , to explain the total electron plus positron spectrum observed by AMS-02 is given in range from 0 to 240 by assuming specific dark matter halo density model, halo propagation model and m B (1) = 1000 GeV [17]. This constraint can be comparable with our result for analysis of the gamma-ray spectrum.…”