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 $\bar 3$ 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 $\pi R$ 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