17,534 research outputs found
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
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 breaking process). This is certainly non--trivial and in fact
imposes interesting constraints on measurable quantities. More precisely, we
find that the gluino mass () and the chargino mass ()
cannot be much higher than their present experimental lower bounds
(GeV ; $M_{\chi^\pm}\stackrel{<}{{}_\sim}80\
\stackrel{>}{{}_\sim} 1\ 80\
\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
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 supergravity
in space-time dimensions can be broken by the supergravity interactions.
The opposite conclusion holds for the dimensionally reduced 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
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