  In this paper we propose a dark matter model and study aspects of its
phenomenology. Our model is based on a new dark matter sector with a U(1)'
gauge symmetry plus a discrete symmetry added to the Standard Model of particle
physics. The new fields of the dark matter sector have no hadronic charges and
couple only to leptons. Our model can not only give rise to the observed
neutrino mass hierarchy, but can also generate the baryon number asymmetry via
non-thermal leptogenesis. The breaking of the new U(1)' symmetry produces
cosmic strings. The dark matter particles are produced non-thermally from
cosmic string loop decay which allows one to obtain sufficiently large
annihilation cross sections to explain the observed cosmic ray positron and
electron fluxes recently measured by the PAMELA, ATIC, PPB-BETS, Fermi-LAT, and
HESS experiments while maintaining the required overall dark matter energy
density. The high velocity of the dark matter particles from cosmic string loop
decay leads to a low phase space density and thus to a dark matter profile with
a constant density core in contrast to what happens in a scenario with
thermally produced cold dark matter where the density keeps rising towards the
center. As a result, the flux of gamma rays radiated from the final leptonic
states of dark matter annihilation from the Galactic center is suppressed and
satisfies the constraints from the HESS gamma-ray observations.
