Infrared Fixed Point Solution for the Top Quark Mass and Unification of Couplings in the MSSM

We analyze the implications of the infrared quasi fixed point solution for the top quark mass in the Minimal Supersymmetric Standard Model. This solution could explain in a natural way the relatively large value of the top quark mass and, if confirmed experimentally, may be suggestive of the onset of nonperturbative physics at very high energy scales. In the framework of grand unification, the expected bottom quark - tau lepton Yukawa coupling unification is very sensitive to the fixed point structure of the top quark mass. For the presently allowed values of the electroweak parameters and the bottom quark mass, the Yukawa coupling unification implies that the top quark mass must be within ten percent of its fixed point values.Comment: 11 pages, 3 figures (not included), MPI-Ph/93-5

Analytic Estimates of the QCD Corrections to Neutrino-Nucleus Scattering

We study the QCD corrections to neutrino deep-inelastic scattering on a nucleus, and analytically estimate their size. For an isoscalar target, we show that the dominant QCD corrections to the ratio of the neutral- to charged-current events are suppressed by sin^4 theta_W, where theta_W is the weak mixing angle. We then discuss the implications for the NuTeV determination of sin^2 theta_W.Comment: 16 pages, Late

Gauge Coupling Constant Unification With Planck Scale Values Of Moduli

Convergence of the standard model gauge coupling constants to a common value at around $2\times 10^{16}$ GeV is studied in the context of orbifold theories where the modular symmetry groups for $T$ and $U$ moduli are broken to subgroups of $PSL(2, Z)$. The values of the moduli required for this unification of coupling constants are studied for this case and also for the case where string unification is accompanied by unification to a gauge group larger then $SU(3)\times SU(2)\times U(1).$Comment: Tex, 15 pages, minor typos corrected and some references adde

Gravitational field around a screwed superconducting cosmic string in scalar-tensor theories

We obtain the solution that corresponds to a screwed superconducting cosmic string (SSCS) in the framework of a general scalar-tensor theory including torsion. We investigate the metric of the SSCS in Brans-Dicke theory with torsion and analyze the case without torsion. We show that in the case with torsion the space-time background presents other properties different from that in which torsion is absent. When the spin vanish, this torsion is a $\phi$-gradient and then it propagates outside of the string. We investigate the effect of torsion on the gravitational force and on the geodesics of a test-particle moving around the SSCS. The accretion of matter by wakes formation when a SSCS moves with speed $v$ is investigated. We compare our results with those obtained for cosmic strings in the framework of scalar-tensor theory.Comment: 22 pages, LaTeX, presented at the "XXII - Encontro Nacional de Fisica de Particulas e Campos", Sao Lourenco, MG, Brazi

A Detailed Study of the Gluino Decay into the Third Generation Squarks at the CERN LHC

In supersymmetric models a gluino can decay into tb\tilde{\chi}^{\pm}_1 through a stop or a sbottom. The decay chain produces an edge structure in the m_{tb} distribution. Monte Carlo simulation studies show that the end point and the edge height would be measured at the CERN LHC by using a sideband subtraction technique. The stop and sbottom masses as well as their decay branching ratios are constrained by the measurement. We study interpretations of the measurement in the minimal supergravity model. We also study the gluino decay into tb and \tilde{\chi}^{\pm}_2 as well as the influence of the stop left-right mixing on the m_{bb} distribution of the tagged $tb$ events.Comment: revtex, 20 pages in PRD format, 35 eps file

Synergistic warm inflation

We consider an alternative warm inflationary scenario in which $n$ scalar fields coupled to a dissipative matter fluid cooperate to produce power--law inflation. The scalar fields are driven by an exponential potential and the bulk dissipative pressure coefficient is linear in the expansion rate. We find that the entropy of the fluid attains its asymptotic value in a characteristic time proportional to the square of the number of fields. This scenario remains nearly isothermal along the inflationary stage. The perturbations in energy density and entropy are studied in the long--wavelength regime and seen to grow roughly as the square of the scale factor. They are shown to be compatible with COBE measurements of the fluctuations in temperature of the CMB.Comment: 13 pages, Revtex 3 To be published in Physical Review

On the exact gravitational lens equation in spherically symmetric and static spacetimes

Lensing in a spherically symmetric and static spacetime is considered, based on the lightlike geodesic equation without approximations. After fixing two radius values r_O and r_S, lensing for an observation event somewhere at r_O and static light sources distributed at r_S is coded in a lens equation that is explicitly given in terms of integrals over the metric coefficients. The lens equation relates two angle variables and can be easily plotted if the metric coefficients have been specified; this allows to visualize in a convenient way all relevant lensing properties, giving image positions, apparent brightnesses, image distortions, etc. Two examples are treated: Lensing by a Barriola-Vilenkin monopole and lensing by an Ellis wormhole.Comment: REVTEX, 11 pages, 12 eps-figures, figures partly improved, minor revision

Neutralino Dark Matter, b-tau Yukawa Unification and Non-Universal Sfermion Masses

We study the implications of minimal non-Universal Boundary Conditions in the sfermion Soft SUSY Breaking (SSB) masses of mSUGRA. We impose asymptotic b-tau Yukawa coupling Unification and we resort to a parameterization of the deviation from Universality in the SSB motivated by the multiplet structure of SU(5) GUT. A set of cosmo-phenomenological constraints, including the recent results from WMAP, determines the allowed parameter space of the models under consideration. We highlight a new coannihilation corridor where neutralino-sbottom and neutralino-tau sneutrino-stau coannihilations significantly contribute to the reduction of the neutralino relic density.Comment: 38 pages, 27 Figures, Latex; Version accepted for publication in PR

Light Gluinos and the Parton Structure of the Nucleon

We study the effects of light gluinos with mass below about 1 GeV on the nucleon parton densities and the running of alpha_(S). It is shown that from the available high-statistics DIS data no lower bound on the gluino mass can be derived. Also in the new kinematical region accessible at HERA the influence of such light gluinos on structure f unctions is found to be very small and difficult to detect. For use in more direct searches involving final state signatures we present a radiative estimate of the gluino distribution in the nucleon.Comment: 23 pages, LateX, 8 figures, MPI-PhT/94-22, LMU-3/9

Bottom-Tau Unification in SUSY SU(5) GUT and Constraints from b to s gamma and Muon g-2

An analysis is made on bottom-tau Yukawa unification in supersymmetric (SUSY) SU(5) grand unified theory (GUT) in the framework of minimal supergravity, in which the parameter space is restricted by some experimental constraints including Br(b to s gamma) and muon g-2. The bottom-tau unification can be accommodated to the measured branching ratio Br(b to s gamma) if superparticle masses are relatively heavy and higgsino mass parameter \mu is negative. On the other hand, if we take the latest muon g-2 data to require positive SUSY contributions, then wrong-sign threshold corrections at SUSY scale upset the Yukawa unification with more than 20 percent discrepancy. It has to be compensated by superheavy threshold corrections around the GUT scale, which constrains models of flavor in SUSY GUT. A pattern of the superparticle masses preferred by the three requirements is also commented.Comment: 21pages, 6figure