A Gauge-Mediation Model with a Light Gravitino of Mass O(10) eV and the Messenger Dark Matter

In the light of recent experimental data on gaugino searches, we revisit the direct-transmission model of dynamical supersymmery breaking with the gravitino mass m_{\tilde{G}}\leq 16 eV, which does not have any cosmological or astrophysical problems. We find that in the consistent regions of parameter space, the model predicts not only upper bounds on superparticle masses (1.1 TeV, 320 GeV, 160 GeV, 5 TeV, 1.5 TeV and 700 GeV for gluino, Wino, Bino, squarks, left-handed sleptons and right-handed sleptons, respectively), but also a mass of the lightest messenger particle in the range of 10-50 TeV. The lightest messenger particle can naturally be a messenger sneutrino. Therefore, this may suggest that the messenger sneutrino could be the dark matter, as proposed recently by Hooper and March-Russel to account for the gamma-ray spectrum from the galactic center observed by HESS experiment.