719 research outputs found
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 GeV is studied in the context of orbifold theories
where the modular symmetry groups for and moduli are broken to
subgroups of . 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 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
-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 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 events.Comment: revtex, 20 pages in PRD format, 35 eps file
Synergistic warm inflation
We consider an alternative warm inflationary scenario in which 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
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