3,839 research outputs found
Exponentially Small Couplings and the Hierarchy Problem
We propose a stringy mechanism whereby a large hierarchy between symmetry
breaking scales is generated. This mechanism is based upon the existence of a
fifth dimension compactified on a segment. We focus on a simple supersymmetric
model with one massless Higgs field in the 3 of SU(3) and another one in the
on each four dimensional end-point of the fifth dimension. Along
supersymmetric flat directions the gauge symmetry is broken down to SU(2) due
to the vacuum expectation value of the Higgs fields on one of the end points.
The remaining massless mode on the other end point acquires a potential due to
a massive five dimensional state propagating between the end points. This
potential breaks the SU(2) symmetry at an exponentially suppressed scale
compared to the SU(3) breaking scale. The suppression factor depends
exponentially on the mass M of the massive state and the length of the
fifth dimension. For reasonably large values of the length scale R one can
achieve a factor of order M_{W}/M_GUT}.Comment: 8 pages, latex, 2 figure
New one-loop techniques and first applications to LHC phenomenology
In this talk we describe our approach for the computation of multi-leg
one-loop amplitudes and present some first results relevant for LHC
phenomenology.Comment: 5 pages, to appear in the proceedings of the conference "Loops and
Legs", Eisenach, 200
Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)
We present a next-to-leading order QCD calculation for single-inclusive
high-p_T jet production in longitudinally polarized pp collisions within the
``small-cone'' approximation. The fully analytical expressions obtained for the
underlying partonic hard-scattering cross sections greatly facilitate the
analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet}
for this process in terms of the unknown polarization of gluons in the nucleon.
We simultaneously rederive the corresponding QCD corrections to unpolarized
scattering and confirm the results existing in the literature. We also
numerically compare to results obtained with Monte-Carlo methods and assess the
range of validity of the ``small-cone'' approximation for the kinematics
relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure
Generalized Gibbs ensembles for time dependent processes
An information theory description of finite systems explicitly evolving in
time is presented for classical as well as quantum mechanics. We impose a
variational principle on the Shannon entropy at a given time while the
constraints are set at a former time. The resulting density matrix deviates
from the Boltzmann kernel and contains explicit time odd components which can
be interpreted as collective flows. Applications include quantum brownian
motion, linear response theory, out of equilibrium situations for which the
relevant information is collected within different time scales before entropy
saturation, and the dynamics of the expansion
Complete resummation of chirally-enhanced loop-effects in the MSSM with non-minimal sources of flavor-violation
In this article we present the complete resummation of the leading
chirally-enhanced corrections stemming from gluino-squark, chargino-sfermion
and neutralino-sfermion loops in the MSSM with non-minimal sources of
flavor-violation. We compute the finite renormalization of fermion masses and
the CKM matrix induced by chirality-flipping self-energies. In the decoupling
limit Msusy>>v, which is an excellent approximation to the full theory, we give
analytic results for the effective gaugino(higgsino)-fermion-sfermion and the
Higgs-fermion-fermion vertices. Using these vertices as effective Feynman
rules, all leading chirally-enhanced corrections can consistently be included
into perturbative calculations of Feynman amplitudes. We also give a
generalized parametrization for the bare CKM matrix which extends the classic
Wolfenstein parametrization to the case of complex parameters lambda and A.Comment: 31 pages, 3 figures; typos correcte
On the photoproduction of jets at HERA
We discuss the inclusive jet production at HERA in the next-to-leading
logarithm approximation. Theoretical uncertainties are considered in some
details. We show the importance of the jet rapidity distribution to constrain
the parton densities in the photon. A comparison is made with the recent H1
data.Comment: 10 + 7 figures included uuencoded tar-compressed
([email protected]) , ENSLAPP-A-484/94, LPTHE Orsay 94-8
Massless D-strings and moduli stabilization in type I cosmology
We consider the cosmological evolution induced by the free energy F of a gas
of maximally supersymmetric heterotic strings at finite temperature and weak
coupling in dimension D>=4. We show that F, which plays the role of an
effective potential, has minima associated to enhanced gauge symmetries, where
all internal moduli can be attracted and dynamically stabilized. Using the fact
that the heterotic/type I S-duality remains valid at finite temperature and can
be applied at each instant of a quasi-static evolution, we find in the dual
type I cosmology that all internal NS-NS and RR moduli in the closed string
sector and the Wilson lines in the open string sector can be stabilized. For
the special case of D=6, the internal volume modulus remains a flat direction,
while the dilaton is stabilized. An essential role is played by light D-string
modes wrapping the internal manifold and whose contribution to the free energy
cannot be omitted, even when the type I string is at weak coupling. As a
result, the order of magnitude of the internal radii expectation values on the
type I side is (lambda_I alpha')^{1/2}, where lambda_I is the ten-dimensional
string coupling. The non-perturbative corrections to the type I free energy can
alternatively be described as effects of "thermal E1-instantons", whose
worldsheets wrap the compact Euclidean time cycle.Comment: 39 pages, 1 figur
- âŠ