Cosmic rays from Leptonic Dark Matter

TL;DR

The paper investigates a leptonic dark matter scenario in which dark matter carries lepton number and decays predominantly to leptons via tiny bilinear R-parity violation, focusing on a right-handed sneutrino LSP. By computing the decay-induced spectra of positrons, gamma rays, and neutrinos, and incorporating Galactic propagation, it shows that a sharp rise in the positron fraction and a diffuse gamma-ray component can be produced with a suppressed antiproton flux, potentially aligning with PAMELA and EGRET observations. The study also discusses non-thermal cosmological production mechanisms to achieve the correct relic abundance and outlines signatures for neutrino detectors and collider experiments. Overall, the work proposes a concrete, testable leptonic DM model that connects high-energy cosmic-ray data to neutrino mass structure and early-universe production processes.

Abstract

If dark matter possesses a lepton number, it is natural to expect the dark-matter annihilation and/or decay mainly produces the standard model leptons, while negligible amount of the antiproton is produced. To illustrate such a simple idea, we consider a scenario that a right-handed sneutrino dark matter decays into the standard model particles through tiny R-parity violating interactions. Interestingly enough, charged leptons as well as neutrinos are directly produced, and they can lead to a sharp peak in the predicted positron fraction. Moreover, the decay of the right-handed sneutrino also generates diffuse continuum gamma rays which may account for the excess observed by EGRET, while the primary antiproton flux can be suppressed. Those predictions on the cosmic-ray fluxes of the positrons, gamma rays and antiprotons will be tested by the PAMELA and FGST observatories.

Figures (4)

• Figure 1: Feynman diagrams of right-handed sneutrino decay via the mixing between the up-type higgsino and the SM leptons.
• Figure 2: Energy spectra of gamma, positron and neutrinos generated from the decay of a $\tilde{\nu}_R$.
• Figure 3: The fraction of positron flux from right-handed sneutrino dark matter decay, shown together with experimental data Barwick:1997igGrimani:2002yzAguilar:2007yfAdriani:2008zr.
• Figure 4: Gamma-ray flux predicted from decay of right-handed sneutrino dark matter, shown together with the EGRET data Sreekumar:1997un.