206 research outputs found
Towards supersymmetric cosmology in M theory
We present a new solution in the heterotic M-theory in which the metric
depends on (cosmic) time. The solution preserves N=1 supersymmetry in 4
dimensions in the leading order of the expansion. It is the
first example of the time-dependent supersymmetric solution in M-theory on
. It describes expanding 4-dimensional space-time with shrinking
orientifold interval and static Calabi-Yau internal space.Comment: latex, 12 page
New brane solutions in higher order gravity
We consider the higher order gravity with dilaton and with the leading string
theory corrections taken into account. The domain wall type solutions are
investigated for arbitrary number of space-time dimensions. The explicit
formulae for the fixed points and asymptotic behavior of generic solutions are
given. We analyze and classify solutions with finite effective gravitational
constant. There is a class of such solutions which have no singularities. We
discuss in detail the relation between fine tuning and self tuning and clarify
in which sense our solutions are fine-tuning free. The stability of such
solutions is also discussed.Comment: 22 pages, Latex, 3 figures; discussion of effective gravitational
constant and of one type of solutions extended; references adde
Higher order dilaton gravity: brane equations of motion in the covariant formulation
Dilaton gravity with general brane localized interactions is investigated.
Models with corrections up to arbitrary order in field derivatives are
considered. Effective gravitational equations of motion at the brane are
derived in the covariant approach. Dependence of such brane equations on the
bulk quantities is discussed. It is shown that the number of the bulk
independent brane equations of motion depends strongly on the symmetries
assumed for the model and for the background. Examples with two and four
derivatives of the fields are presented in more detail.Comment: 32 pages, references added, discussion extended, typos corrected,
version to be publishe
Effects of Supersymmetric Threshold Corrections on High-Scale Flavor Textures
Integration of superpartners out of the spectrum induces potentially large
contributions to Yukawa couplings. These corrections, the supersymmetric
threshold corrections, therefore influence the CKM matrix prediction in a
non-trivial way. We study effects of threshold corrections on high-scale flavor
structures specified at the gauge coupling unification scale in supersymmetry.
In our analysis, we first consider high-scale Yukawa textures which qualify
phenomenologically viable at tree level, and find that they get completely
disqualified after incorporating the threshold corrections. Next, we consider
Yukawa couplings, such as those with five texture zeroes, which are incapable
of explaining flavor-changing proceses. Incorporation of threshold corrections,
however, makes them phenomenologically viable textures. Therefore,
supersymmetric threshold corrections are found to leave observable impact on
Yukawa couplings of quarks, and any confrontation of high-scale textures with
experiments at the weak scale must take into account such corrections.Comment: 25 pages, submitted to JHE
Domain walls without cosmological constant in higher order gravity
We consider a class of higher order corrections with arbitrary power of
the curvature tensor to the standard gravity action in arbitrary space-time
dimension . The corrections are in the form of Euler densities and are
unique at each and . We present a generating functional and an explicit
form of the corresponding conserved energy-momentum tensors. The case of
conformally flat metrics is discussed in detail. We show that this class of
corrections allows for domain wall solutions since, despite the presence of
higher powers of the curvature tensor, the singularity structure at the wall is
of the same type as in the standard gravity. However, models with higher order
corrections have larger set of domain wall solutions and the existence of these
solutions no longer depends on the presence of cosmological constants. We find
for example that the Randall-Sundrum scenario can be realized without any need
for bulk and/or brane cosmological constant.Comment: latex, 10 pages, introduction extended, references added, typos
correcte
Supersymmetric Electroweak Renormalization of the Z-Width in the MSSM (I)
Within the framework of the MSSM, we compute the complete set of electroweak
one-loop supersymmetric quantum effects on the width of the
-boson in the on-shell renormalization scheme. Numerical analyses of the
corrections to the various partial widths into leptons and quarks are
presented. On general grounds, the average size of the electroweak SUSY
corrections to may well saturate the level of the present
theoretical uncertainties, even if considering the full supersymmetric spectrum
lying in the neighbourhood of the unaccessible LEP 200 range. Remarkably
enough, for the present values of the top quark mass, the electroweak SUSY
effects could be, globally, very close or even bigger than the electroweak SM
corrections, but opposite in sign. Therefore, in the absence of theoretical
errors, there are large regions of parameter space where one could find that,
effectively, the electroweak SM corrections are ``missing'', or even having the
``wrong'' sign. This should be helpful in discriminating between the SM and the
MSSM. However, an accurate prediction of the electroweak quantum effects on
will only be possible, if and are pinned down
in the future with enough precision.Comment: 17 p. in LaTeX. Preprint UAB-FT-343. Error in figure caption #3
corrected. Results unchange
Sparticle Mass Spectra from SO(10) Grand Unified Models with Yukawa Coupling Unification
We examine the spectrum of superparticles obtained from the minimal SO(10)
grand unified model, where it is assumed the gauge symmetry breaking yields the
Minimal Supersymmetric Standard Model (MSSM) as the effective theory at
GeV. In this model, unification of Yukawa
couplings implies a value of . At such high values of
, assuming universality of scalar masses, the usual mechanism of
radiative electroweak symmetry breaking breaks down. We show that a set of weak
scale sparticle masses consistent with radiative electroweak symmetry breaking
can be generated by imposing non-universal GUT scale scalar masses consistent
with universality within SO(10) plus extra -term contributions associated
with the reduction in rank of the gauge symmetry group when SO(10)
spontaneously breaks to . We comment upon the
consequences of the sparticle mass spectrum for collider searches for
supersymmetry. One implication of SO(10) unification is that the light bottom
squark can be by far the lightest of the squarks. This motivates a dedicated
search for bottom squark pair production at and colliders.Comment: 12 page REVTEX file including 3 PS figures; revised manuscript
includes minor changes to coincide with published versio
Do electroweak precision data and Higgs-mass constraints rule out a scalar bottom quark with mass of O(5 GeV)?
We investigate the phenomenological implications of a light scalar bottom
quark, with a mass of about the bottom quark mass, within the minimal
supersymmetric standard model. The study of such a scenario is of theoretical
interest, since, depending on their production and decay modes, light sbottoms
may have escaped experimental detection up to now and, in addition, may
naturally appear for large values of \tan\beta. In this article we show that
such a light sbottom cannot be ruled out by the constraints from the
electroweak precision data and the present bound on the lightest CP-even Higgs
boson mass at LEP. It is inferred that a light sbottom scenario requires in
general a relatively light scalar top quark whose mass is typically about the
top-quark mass. It is also shown that under these conditions the lightest
CP-even Higgs boson decays predominantly into scalar bottom quarks in most of
the parameter space and that its mass is restricted to m_h ~< 123 GeV.Comment: 7 pages, 2 figures, LateX. Discussion about fine tuning and
low-energy experiments enlarged. Version to appear in Phys. Rev. Let
Perspectives for Detection of a Higgsino-like Relic Neutralino
It has been conjectured by Ambrosanio, Kane, Kribs, Martin and Mrenna (AKM)
that the CDF event is due to
a decay chain involving two neutralino states (the lightest and the
next-to-lightest ones). The lightest neutralino () has been further
considered by Kane and Wells as a candidate for cold dark matter. In this paper
we examine the properties of relic 's in their full parameter
space, and examine the perspectives for detection by comparing theoretical
predictions to sensitivities of various experimental searches. We find that for
most regions of the parameter space the detectability of a relic
would require quite substantial improvements in current experimental
sensitivities. The measurements of neutrino fluxes from the center of the Earth
and of an excess of in cosmic rays are shown to offer some
favorable perspectives for investigating a region of the parameter
space around the maximal value allowed by the model.Comment: 16 pages, LaTeX, 10 postscript figure
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