$SU(2{)}_L$ triplet scalars appear in models motivated for the left-right symmetry, neutrino masses, and dark matter (DM), etc. If the triplets are the main decay products of the DM particle, and carry nonzero lepton numbers, they may decay dominantly into lepton pairs, which can naturally explain the current experimental results reported by PAMELA and Fermi-LAT or ATIC. We discuss this possibility in an extended left-right symmetric model in which the decay of the DM particle is induced by tiny soft charge-conjugation ($C$) violating interactions, and calculate the spectra for cosmic-ray positrons, neutrinos, and gamma rays. We show that the DM signals in the flux of high energy neutrinos can be significantly enhanced, as the triplets couple to both charged leptons and neutrinos with the same strength. In this scenario, the predicted neutrino-induced muon flux can be several times larger than the case in which the DM particle only directly decays into charged leptons. In addition, the charged components of the triplet may give an extra contribution to the high energy gamma rays through an internal bremsstrahlung process, which depends on the mass hierarchy between the DM particle and the triplet scalars.

• Received 20 January 2010

DOI:https://doi.org/10.1103/PhysRevD.81.075014