Implications of Two-component Dark Matter Induced by Forbidden Channels and Thermal Freeze-out

We consider a model of two-component dark matter based on a hidden $U(1)_D$ symmetry, in which relic densities of the dark matter are determined by forbidden channels and thermal freeze-out. The hidden $U(1)_D$ symmetry is spontaneously broken to a residual $\mathbb{Z}_4$ symmetry, and the lightest $\mathbb{Z}_4$ charged particle can be a dark matter candidate. Moreover, depending on the mass hierarchy in the dark sector, we have two-component dark matter. We show that the relic density of the lighter dark matter component can be determined by forbidden annihilation channels which require larger couplings compared to the normal freeze-out mechanism. As a result, a large self-interaction of the lighter dark matter component can be induced, which may solve small scale problems of $\Lambda$CDM model. On the other hand, the heavier dark matter component is produced by normal freeze-out mechanism. We find that interesting implications emerge between the two dark matter components in this framework. We explore detectabilities of these dark matter particles and show some parameter space can be tested by the SHiP experiment.Comment: 23 pages, 9 figures, 1 table, version to appear in JCA

Physics potential of future long baseline neutrino oscillation experiments with KEK-JAERI HIPA

We study physics potential of Very Long Base-Line (VLBL) Neutrino-Oscillation Experiments with the High Intensity Proton Accelerator, which will be completed by the year 2007 in Tokai-village, Japan. As a target, a 100 kton-level water-$\check {\rm C}$erenkov detector is considered at 2,100 km away. Assuming the pulsed narrow-band $\nu_\mu$ beams, we study sensitivity of such experiments to the neutrino mass hierarchy, the mass-squared differences, one CP phase and three angles of the lepton-flavor-mixing matrix. We find that experiments at a distance 2,100 km can determine the neutrino mass hierarchy if the mixing matrix element $|U_{e3}|$ is not too small. The CP phase and $|U_{e3}|$ can be constrained if the large-mixing-angle solution of the solar-neutrino deficit is realized.Comment: 6 pages, LaTeX, Talk given at 5th KEK Topical Conference (KEKTC5), KEK, Tsukuba, Japan, November 200