Self-tuning of cosmological constant and exit from inflation

I review the recent 5D self-tuning solutions of the cosmological constant problem, and try to unify two cosmological constant problems within the framework of the self-tuning solutions. One problem, the large cosmological constant needed for inflation, is interpreted by starting with the parameters allowing only the dS vacuum, and the vanishing cosmological constant at a true vacuum is realized by changing parameters by exit from inflation at the brane such that the self-tuning solution is allowed.Comment: Latex file of 8 pages, including 2 figures. Talk presented at COSPA-03, Taipei, Taiwan, Nov. 13-15, 200

R-parity from string compactification

In this paper, we embed the $\Z_{4R}$ parity as a discrete subgroup of a global symmetry \UoR\,obtained from $\Z_{12-I}$ compactification of heterotic string \EE8. A part of \UoR\,transformation is the shift of the anticommuting variable $\vartheta$ to $e^{i\alpha}\vartheta$ which necessarily incoorporate the transformation of internal space coordinate. Out of six internal spaces, we identify three U(1)'s whose charges are denoted as $Q_{18},Q_{20}$, and $Q_{22}$. The \UoR~is defined as \UEE$\times$\UKK~where \UEE~is the part from \EE8 and \UKK~is the part generated by $Q_{18},Q_{20}$, and $Q_{22}$. We propose a method to define a \UoR~direction. The needed vacuum expectation values for breaking gauge U(1)'s except U(1)$_Y$ of the standard model carry \UoR~charge 4 modulo 4 such that \UoR~is broken down to $\Z_{4R}$ at the grand unification scale. $\Z_{4R}$ is broken to $\Z_{2R}$ between the intermediate (\sim 10^{11\,}\gev) and the electroweak scales (100\,\gev\sim 1\,\tev). The conditions we impose are proton longevity, a large top quark mass, and acceptable magnitudes for the $\mu$ term and neutrino masses.Comment: 21 pages with 3 figure

Is an axizilla possible for di-photon resonance?

Heavy axion-like particles, called axizillas, are simple extensions of the standard model(SM). An axizilla is required not to couple to the quarks, leptons, and Brout-Englert-Higgs doublets of the SM, but couple to the gauge anomalies of the $W^\pm, Z$ and photon. It is possible to have its branching ratios(BRs) to two photons greater than 10% and to two $Z$'s less than 10%. To have a (production cross section)$\cdot$(BR to di-photons) at a $10^{-38}\,\textrm{cm}^2$ level, a TeV scale heavy quark $Q$ is required for the gluon--quark fusion process. The decay of $Q$ to axizilla plus quark, and the subsequent decay of the axizilla to two photons can be fitted at the required level of $10^{-38}\,\textrm{cm}^2$.Comment: 9 pages of latex file with 3 figure