Abstract
We present a supersymmetric model with two dark matter (DM)components explaining the galactic positron excess observed byPAMELA/HEAT and ATIC/PPB-BETS: One is the conventional (bino-like)lightest supersymmetric particle (LSP) χ, and the other is aTeV scale meta-stable neutral singlet ND, which is a Diracfermion (N,Nc). In this model, ND decays dominantly intoχe+e− through an R parity preserving dimension 6operator with the life time τN ∼ 1026 sec. We introducea pair of vector-like superheavy SU(2) lepton doublets (L,Lc)and lepton singlets (E,Ec). The dimension 6 operator leading tothe ND decay is generated from the leptophilic Yukawainteractions by W ⊃ NecE+LhdEc+m3/2l1Lc with thedimensionless couplings of order unity, and the gauge interactionby ℒ ⊃ (2)1/2g′ẽc*ecχ+h.c. Thesuperheavy masses of the vector-like leptons (ML,ME ∼ 1016 GeV) are responsible for the longevity of ND. The lowenergy field spectrum in this model is just the MSSM fields andND.Even for the case that the portion of ND is much smaller thanthat of χ in the total DM density [\U0001d4aa(10−10) ≲ nND/nχ], the observed positron excess can beexplained by adopting relatively lighter masses of the vector-likeleptons (1013 GeV ≲ ML,E ≲ 1016 GeV).The smallness of the electron mass is also explained. This modelis easily embedded in the flipped SU(5) grand unification, whichis a leptophilic unified theory.
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