Dark Matter: The Leptonic Connection

Abstract

Recent observatons of high-energy positrons and electrons by the PAMELA and ATIC experiments may be an indication of the annihilation of dark matter into leptons and not quarks. This leptonic connection was foreseen already some years ago in two different models of radiative neutrino mass. We discuss here the generic interactions (nu eta^0 - l eta^+) chi and l^c zeta^- chi^c which allow this to happen, where chi and/or chi^c are fermionic dark-matter candidates. We point out in particular the importance of chi chi to l^+ l^- gamma to both positron and gamma-ray signals within this framework.

Figures (5)

• Figure 1: Correlation between $m_{\chi}$ and $m_{\eta}$, giving rise to the correct amount of relic abundance for different Yukawa coupling strengths: (a) and (b) for Majorana $\chi$, (c) and (d) for Dirac $\chi$. The shadow region where $m_{\chi}>m_{\eta}$ is excluded.
• Figure 2: Cross sections for the direct detection of $\chi$: (a) Majorana case, SD only; (b) Dirac case, both SD and SI.
• Figure 3: Feynman diagrams of the bremstrahlung annihilation process.
• Figure 4: Energy spectrum of the gamma-ray (black curve) and positron (red curve) in the limit of $v\to0$ for $\chi \chi \to e^+ e^- \gamma$ with various values of $m_{\chi}$ and $m_{\eta}$.
• Figure 5: Positron fraction in the leptonic dark matter scenario with $M_\chi=450$ GeV and $m_\eta=500$ GeV for $\chi$ Majorana and Dirac.