Two-Loop Helicity Amplitudes for Gluon-Gluon Scattering in QCD and Supersymmetric Yang-Mills Theory

We present the two-loop helicity amplitudes for the scattering of two gluons into two gluons in QCD, which are relevant for next-to-next-to-leading order corrections to jet production at hadron colliders. We give the results in the `t Hooft-Veltman and four-dimensional helicity variants of dimensional regularization. Summing our expressions over helicities and colors, and converting to conventional dimensional regularization, gives results in complete agreement with those of Glover, Oleari and Tejeda-Yeomans. We also present the amplitudes for 2 to 2 scattering in pure N=1 supersymmetric Yang-Mills theory.Comment: 55 pages, 3 figures, corrected remark below eq. (4.33), other minor changes, version appearing in JHE

Minimal String Unification and Hidden Sector in Z_8 Orbifold Models

We study the minimal supersymmetric standard model derived from the $Z_8$ orbifold models and its hidden sectors. We use a target-space duality anomaly cancellation so as to investigate hidden sectors consistent with the MSSM unification. For the allowed hidden sectors, we estimate the running gauge coupling constants making use of threshold corrections due to the higher massive modes. The calculation is important from the viewpoint of gaugino condensations, which is one of the most promissing mechanism to break the supersymmetry.Comment: 14 pages, KANAZAWA-93-11, LaTeX fil

Soft SUSY Breaking Terms in Stringy Scenarios: Computation and Phenomenological Viability

We calculate the soft SUSY breaking terms arising from a large class of string scenarios, namely symmetric orbifold constructions, and study its phenomenological viability. They exhibit a certain lack of universality, unlike the usual assumptions of the minimal supersymmetric standard model. Assuming gaugino condensation in the hidden sector as the source of SUSY breaking, it turns out that squark and slepton masses tend to be much larger than gaugino masses. Furthermore, we show that these soft breaking terms can be perfectly consistent with both experimental and naturalness constraints (the latter comes from the absence of fine tuning in the $SU(2)\times U(1)_Y\rightarrow U(1)_{em}$ breaking process). This is certainly non--trivial and in fact imposes interesting constraints on measurable quantities. More precisely, we find that the gluino mass ($M_3$) and the chargino mass ($M_{\chi^{\pm}}$) cannot be much higher than their present experimental lower bounds ($M_3\stackrel{<}{{}_\sim}285\$GeV ; $M_{\chi^\pm}\stackrel{<}{{}_\sim}80\ $GeV), while squark and slepton masses must be much larger ($\stackrel{>}{{}_\sim} 1\ $TeV). This can be considered as an observational signature of this kind of stringy scenarios. Besides, the top mass is constrained to be within a range ($80\ $GeV$\stackrel{<}{{}_\sim}m_t\stackrel{<}{{}_\sim}165\ $GeV)Comment: 18 pages, CERN-TH.6681/9

Discrete Torsion and WZW Orbifolds

We propose a geometrical interpretation for the discrete torsion appearing in the algebraic formulation of quotients of WZW models by discrete abelian subgroups. Part of the discrete torsion corresponds to the choice of action of the subgroup, yielding different quotient spaces. Another part corresponds to the set of different choices of connection for the H field in each of these spaces. The former is for instance used to describe generalized lens spaces L(n,p).Comment: 11 pages, no figures; references added, typos correcte

QCD and QED Corrections to Light-by-Light Scattering

We present the QCD and QED corrections to the fermion-loop contributions to light-by-light scattering, gamma gamma to gamma gamma, in the ultrarelativistic limit where the kinematic invariants are much larger than the masses of the charged fermions.Comment: 17 pages, 3 figure files, JHEP styl

Package ecespa

Documentation for the R-package "ecespa

Duality-Invariant Gaugino Condensation and One-Loop Corrected Kahler Potentials in String Theory

The duality-invariant gaugino condensation with or without massive matter fields is re-analysed, taking into account the dependence of the string threshold corrections on the moduli fields and recent results concerning one-loop corrected K\"ahler potentials. The scalar potential of the theory for a generic superpotential is also calculated.Comment: 18 page

Threshold Corrections to Gauge Couplings in Orbifold Compactifications

We derive the moduli dependent threshold corrections to gauge couplings in toroidal orbifold compactifications. The underlying six dimensional torus lattice of the heterotic string theory is not assumed ---as in previous calculations--- to decompose into a direct sum of a four--dimensional and a two--dimensional sublattice, with the latter lying in a plane left fixed by a set of orbifold twists. In this more general case the threshold corrections are no longer automorphic functions of the modular group, but of certain congruence subgroups of the modular group. These groups can also be obtained by studying the massless spectrum; moreover they have larger classes of automorphic functions. As a consequence the threshold corrections cannot be uniquely determined by symmetry considerations and certain boundary conditions at special points in the moduli space, as was claimed in previous publications.Comment: 20 pages (Latex) (There was a minor Latex error in the original version. This is removed now

Broken sigma-model isometries in very special geometry

We show that the isometries of the manifold of scalars in $N=2$ supergravity in $d=5$ space-time dimensions can be broken by the supergravity interactions. The opposite conclusion holds for the dimensionally reduced $d=4$ theories, where the isometries of the scalar manifold are always symmetries of the full theory. These spaces, which form a subclass of the {\em special} K\"ahler manifolds, are relevant for superstring compactifications.Comment: 10 page