Threshold corrections in orbifold models and superstring unification of gauge interactions

The string one loop renormalization of the gauge coupling constants is examined in abelian orbifold models. The contributions to string threshold corrections independent of the compactification moduli fields are evaluated numerically for several representative examples of orbifold models. We consider cases with standard and non-standard embeddings as well as cases with discrete Wilson lines background fields which match reasonably well with low energy phenomenology. We examine one loop gauge coupling constants unification in a description incorporating the combined effects of moduli dependent and independent threshold corrections, an adjustable Kac-Moody level for the hypercharge group factor and a large mass threshold associated with an anomalous $U(1)$ mechanism.Comment: 24 pages. 2 figures. Revised version: Several misprints corrected. Few minor additions

R-parity violation and the cosmological gravitino problem

Based on the R-parity violation option of the minimal supersymmetric Standard Model, we examine the scenario where the massive gravitino, relic from the hot big-bang, is the lightest supersymmetric particle and can decay through one or several of the trilinear R-parity violating interactions. We calculate the rates of the gravitino decay via the various three-body decay channels with final states involving three quarks and/or leptons. By taking into account the present constraints on the trilinear R-parity violating coupling constants and assuming the gravitino and scalar superpartner masses do not exceed ${\cal O}(10TeV)$, it turns out that the gravitinos could easily have decayed before the present epoch but not earlier than the big-bang nucleosynthesis one. Therefore, the considered scenario would upset the standard big-bang nucleosynthesis and we conclude that it does not seem to constitute a natural solution for the cosmological gravitino problem.Comment: 22 pages, Latex file, 5 figure

Chiral symmetry breaking in strongly coupled scalar QED

Scalar QED with fermions is investigated in an expansion in powers of the inverse gauge coupling constant. The fermion mass generation is studied in next to leading order of the strong coupling expansion for the Higgs-phase of the model. Chiral symmetry breaking is discussed. Our approach supports from a strong coupling point of view the results obtained earlier by Miransky, Bardeen and Kondo.Comment: 17 pages, 2 figures, complete uu-file avaiable on reques

Implications of vacuum stability constraints on the nonminimal supersymmetric standard model with lepton number violation

We carry out a detailed analysis of the scalar sector of the nonminimal supersymmetric standard model with lepton number violation, and study the constraints imposed on it by the stability of the electroweak symmetry breaking vacuum. The model contains a trilinear lepton mumber violating term in the superpotential together with the associated \susy breaking interactions which can give rise to neutrino masses. We evaluate the mass matrices for the various boson and fermion modes and then discuss the effect that the lepton number violating interactions have on the mass spectra using a phenomenological precription to implement the experimental constraints on the light neutrinos mass matrix. We also discuss qualitatively the conditions on the lepton number violating parameters set by the unbounded from below directions, and from the absence of the charge and color breaking minima in this model.Comment: 39 pages, 5 figures, Latex file, ps figure

Neutron Electric Dipole Moment in Two Higgs Doublet Model

We study the effect of the "chromo-electric" dipole moment on the electric dipole moment(EDM) of the neutron in the two Higgs doublet model. We systematically investigate the Weinberg's operator O_{3g}=GG\t G and the operator O_{qg}=\bar q\sigma\t Gq, in the cases of \tan\b\gg 1, \tan\b\ll 1 and \tan\b\simeq 1. It is shown that $O_{sg}$ gives the main contribution to the neutron EDM compared to the other operators, and also that the contributions of $O_{ug}$ and $O_{3g}$ cancel out each other. It is pointed out that the inclusion of second lightest neutral Higgs scalar adding to the lightest one is of essential importance to estimate the neutron EDM. The neutron EDM is considerably reduced due to the destructive contribution with each other if the mass difference of the two Higgs scalars is of the order O(50\G).Comment: 20 pages with 12 figures. Figures will be sent by postal mail if requested. Late

Resonant sneutrino production at Tevatron Run II

We consider the single chargino production at Tevatron $p \bar p \to \tilde \nu_i \to \tilde \chi^{\pm}_1 l_i^{\mp}$ as induced by the resonant sneutrino production via a dominant \RPV coupling of type \l'_{ijk} L_i Q_j D_k^c. Within a supergravity model, we study the three leptons final state. The comparison with the expected background demonstrate that this signature allows to extend the sensitivity on the \susyq mass spectrum beyond the present LEP limits and to probe the relevant \RPV coupling down to values one order of magnitude smaller than the most stringent low energy indirect bounds. The trilepton signal offers also the opportunity to reconstruct the neutralino mass in a model independent way with good accuracy.Comment: 4 page

Timescales and mechanisms of formation of amorphous silica coatings on fresh basalts at Kilauea Volcano, Hawai’i

Young basalts from Kilauea Volcano, Hawai'i, frequently feature opaque surface coatings, 1–80 μm thick, composed of amorphous silica and Fe-Ti oxides. These coatings are the product of interaction of the basaltic surface with volcanically-derived acidic fluids. Previous workers have identified these coatings in a variety of contexts on Hawai'i, but the timescales of coating development, coating growth rates, and factors controlling lateral coating heterogeneity were largely unconstrained. We sampled and analyzed young lava flows (of varying ages, from hours to ~ 40 years) along Kilauea's southwest and east rift zones to characterize variation in silica coating properties across the landscape. Coating thickness varies as a function of flow age, flow surface type, and proximity to acid sources like local fissure vents and regional plumes emitted from Kilauea Caldera and Pu'u O'o. Silica coatings that form in immediate proximity to acid sources are more chemically pure than those forming in higher pH environments, which contain significant Al and Fe. Incipient siliceous alteration was observed on basalt surfaces as young as 8 days old, but periods of a year or more are required to develop contiguous coatings with obvious opaque coloration. Inferred coating growth rates vary with environmental conditions but were typically 1-5 μm/year. Coatings form preferentially on flow surfaces with glassy outer layers, such as spatter ramparts, volcanic bombs and dense pahoehoe breakouts, due to glass strain weakening during cooling. Microtextural evidence suggests that the silica coatings form both by in situ dissolution-reprecipitation and by deposition of silica mobilized in solution. Thin films of water, acidified by contact with volcanic vapors, dissolved near-surface basalt, then precipitated amorphous silica in place, mobilizing more soluble cations. Additional silica was transported to and deposited on the surface by silica-bearing altering fluids derived from the basalt interior

Two-pion-exchange parity-violating potential and n⃗p→dγ\vec{n} p \to d \gamma

We calculate the parity-violating nucleon-nucleon potential in heavy-baryon chiral perturbation theory up to the next-to-next-to-leading order. The one-pion exchange comes in the leading order and the next-to-next-to-leading order consists of two-pion-exchange and the two-nucleon contact terms. In order to investigate the effect of the higher order contributions, we calculate the parity-violating asymmetry in $\vec{n} p \to d \gamma$ at the threshold. The one-pion dominates the physical observable and the two-pion contribution is about or less than 10% of the one-pion contribution.Comment: 3 pages, contribution to the workshop PAVI06 held in Milos island, Greece, May 16-20, 200