PAMELA's cosmic positron from decaying LSP in SO(10) SUSY GUT

We propose two viable scenarios explaining the recent observations on cosmic positron excess. In both scenarios, the present relic density in the Universe is assumed to be still supported by thermally produced WIMP or LSP (\chi). One of the scenarios is based on two dark matter (DM) components (\chi,X) scenario, and the other is on SO(10) SUSY GUT. In the two DM components scenario, extremely small amount of non-thermally produced meta-stable DM component [O(10^{-10}) < n_X /n_\chi] explains the cosmic positron excess. In the SO(10) model, extremely small R-parity violation for LSP decay to e^\pm is naturally achieved with a non-zero VEV of the superpartner of one right-handed neutrino (\tilde{\nu}^c) and a global symmetry.Comment: 6 pages, Talks presented in PASCOS, SUSY, and COSMO/CosPA in 201

GUT Scale And Leptogenesis From 5D Inflation

We discuss a five dimensional inflationary scenario based on a supersymmetric SO(10) model compactified on $S^1/(Z_2\times Z_2')$. Inflation is implemented through scalar potentials on four dimensional branes, and a brane-localized Einstein-Hilbert term plays an essential role. The orbifold boundary conditions break the SO(10) gauge symmetry to $SU(4)_c\times SU(2)_L\times SU(2)_R$ ($\equiv H$). The inflationary scenario yields $\delta T/T\propto (M/M_{\rm Planck})^2$, which fixes $M$, the symmetry breaking scale of $H$ to be close to the SUSY GUT scale of $10^{16}$ GeV. The scalar spectral index $n$ is $0.98-0.99$, while the gravitational wave contribution to the quadrupole anisotropy is negligible (\lapproxeq 1 {%}). The inflaton decay into the lightest right handed neutrinos yields the observed baryon asymmetry via leptogenesis

4D gravity on a brane from bulk higher-curvature terms

We study a gravity model where a tensionful codimension-one three-brane is embedded on a bulk with infinite transverse length. We find that 4D gravity is induced on the brane already at the classical level if we include higher-curvature (Gauss-Bonnet) terms in the bulk. Consistency conditions appear to require a negative brane tension as well as a negative coupling for the higher-curvature terms.Comment: 10 pages, no figures; a minor change in wording (to appear in MPLA

Brane gravity, massless bulk scalar and self-tuning of the cosmological constant

We show that a self-tuning mechanism of the cosmological constant could work in 5D non-compact space-time with a $Z_2$ symmetry in the presence of a massless scalar field. The standard model matter fields live only on the 4D brane. The change of vacuum energy on the brane (brane cosmological constant) by, for instance, electroweak and QCD phase transitions, just gives rise to dynamical shifts of the profiles of the background metric and the scalar field in the extra dimension, keeping 4D space-time flat without any fine-tuning. To avoid naked singularities in the bulk, the brane cosmological constant should be negative. We introduce an additional brane-localized 4D Einstein-Hilbert term so as to provide the observed 4D gravity with the non-compact extra dimension. With a general form of brane-localized gravity term allowed by the symmetries, the low energy Einstein gravity is successfully reproduced on the brane at long distances. We show this phenomenon explicitly for the case of vanishing bulk cosmological constant.Comment: 1+15 pages, no figure, Version to appear in PR