526 research outputs found

### 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

### 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

### Contact interactions in low scale string models with intersecting $D6$-branes

We evaluate the tree level four fermion string amplitudes in the TeV string
mass scale models with intersecting $D6$-branes. The coefficient functions of
contact interactions subsuming the contributions of string Regge resonance and
winding mode excitations are obtained by subtracting out the contributions from
the string massless and massive momentum modes. Numerical applications are
developed for the Standard Model like solution of Cremades, Ibanez, and
Marchesano for a toroidal orientifold with four intersecting $D6$-brane stacks.
The chirality conserving contact interactions of the quarks and leptons are
considered in applications to high energy collider and flavor changing neutral
current phenomenology. The two main free parameters consist of the string and
compactification mass scales, $m_s$ and $M_c$. Useful constraints on these
parameters are derived from predictions for the Bhabha scattering differential
cross section and for the observables associated to the mass shifts of the
neutral meson systems $K-\bar K, B-\bar B, D-\bar D$ and the lepton number
violating three-body leptonic decays of the charged leptons $\mu$ and $\tau$.Comment: 34 pages, 7 figure

### 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

### 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

### Quenching of the Deuteron in Flight

We investigate the Lorentz contraction of a deuteron in flight. Our starting
point is the Blankenbecler-Sugar projection of the Bethe-Salpeter equation to a
3-dimensional quasi potential equation, wqhich we apply for the deuteron bound
in an harmonic oscillator potential (for an analytical result) and by the Bonn
NN potential for a more realistic estimate. We find substantial quenching with
increasing external momenta and a significant modification of the high momentum
spectrum of the deuteron.Comment: 11 pages, 4 figure

### Nonminimal supersymmetric standard model with lepton number violation

We carry out a detailed analysis of the nonminimal supersymmetric standard
model with lepton number violation. The model contains a unique trilinear
lepton number violating term in the superpotential which can give rise to
neutrino masses at the tree level. We search for the gauged discrete symmetries
realized by cyclic groups which preserve the structure of the associated
trilinear superpotential of this model, and which satisfy the constraints of
the anomaly cancellation. The implications of this trilinear lepton number
violating term in the superpotential and the associated soft supersymmetry
breaking term on the phenomenology of the light neutrino masses and mixing is
studied in detail. We evaluate the tree and loop level contributions to the
neutrino mass matrix in this model. We search for possible suppression
mechanism which could explain large hierarchies and maximal mixing angles.Comment: Latex file, 43 pages, 2 figure

### Nucleon decay in gauge unified models with intersecting D6-branes

Baryon number violation is discussed in gauge unified orbifold models of type
II string theory with intersecting Dirichlet branes. We consider setups of
D6-branes which extend along the flat Minkowski space-time directions and wrap
around 3-cycles of the internal 6-d manifold. The discussion is motivated by
the enhancement effect of low energy amplitudes anticipated for M-theory and
type II string theory models with matter modes localized at points of the
internal manifold. The conformal field theory formalism is used to evaluate the
open string amplitudes at tree level. We study the single baryon number
violating processes of dimension 6 and 5, involving four quarks and leptons and
in supersymmetry models, two pairs of matter fermions and superpartner
sfermions. The higher order processes associated with the baryon number
violating operators of dimension 7 and 9 are also examined, but in a
qualitative way. We discuss the low energy representation of string theory
amplitudes in terms of infinite series of poles associated to exchange of
string Regge resonance and compactification modes. The comparison of string
amplitudes with the equivalent field theory amplitudes is first studied in the
large compactification radius limit. Proceeding next to the finite
compactification radius case, we present a numerical study of the ratio of
string to field theory amplitudes based on semi-realistic gauge unified
non-supersymmetric and supersymmetric models employing the Z3 and Z2xZ2
orbifolds. We find a moderate enhancement of string amplitudes which becomes
manifest in the regime where the gauge symmetry breaking mass parameter exceeds
the compactification mass parameter, corresponding to a gauge unification in a
seven dimensional space-time.Comment: 63 pages revtex4. 8 postscript figures. 4 tables. Subsection II.B
revised. Several new references added. To appear in Physical Review

- …