An SU(5) SUSY Model with R-Parity Violation and Radiatively Induced Neutrino Masses

The radiatively induced neutrino mass matrix is investigated on the basis of an SU(5) SUSY model. In order to evade the proton decay, an ansatz based on a discrete symmetry $Z_2$ is assumed: although, at the unification scale, we have two types of superfields $\Psi_{L(\pm)}=\bar{5}_{L(\pm)}+10_{L(\pm)}$, which are transformed as $\Psi_{L(\pm)} \to \pm \Psi_{L(\pm)}$ under the discrete symmetry Z$_2$, the particles $\Psi_{L(+)}$ are decoupled after the SU(5) symmetry is broken, so that our quarks and leptons belong to \Psi_{L(-)}. The R-parity-violating terms for our quarks and leptons \Psi_{L(-)} are basically forbidden under the symmetry Z_2. However, we assume that mixings between members of \Psi_{L(+)} and those of \Psi_{L(-)} are in part caused after SU(5) is broken. As a result, the R-parity-violating interactions are in part allowed, so that the neutrino masses are radiatively generated, while the proton decay due to the R-parity violating terms is still forbidden because the term d_R^c d_R^c u_R^c has z=-1.Comment: 6 pages, Revtex, no figur

Heating experiments of carbon grains: Implication for the origin of interstellar dust

Amorphous carbonaceous grains produced in a methane gas atmosphere were analyzed by high resolution transmission electron microscope (HRTEM). Structural alteration of the amorphous carbonaceous grains was directly observed by in situ HRTEM observation. The specimen was heated to a maximum of 550℃. The HRTEM image of a prepared specimen showed the structure of the onion-like carbon. The onion-like structure distorted at 100℃, which suggested the evaporation of -OH groups included in the grains. Upon heating to 260℃, the centers of the onion-like grains formed holes of the order of 3 nm in size. On further heating to 550℃, the structure of the chained grains with a size of 10 nm changed to graphite sheets with a length of 50 nm by the surface melting coalescence among chained grains. The structural changes at the above temperatures have been observed only in amorphous carbonaceous grains produced in a methane gas atmosphere and have been attributed to the existence of hydrogen in the grains