1,860 research outputs found
On Heterotic/Type I Duality in d=8
We discuss heterotic corrections to quartic internal U(1) gauge couplings and
check duality by calculating one-loop open string diagrams and identifying the
D-instanton sum in the dual type I picture. We also compute SO(8)^4 threshold
corrections and finally R^2 corrections in type I theory.Comment: 9 pages, Latex, To appear in the proceedings of "Quantum Aspects of
Gauge Theories, Supersymmetries and Unification", Corfu, September 199
Generalized Calabi-Yau Manifolds and the Mirror of a Rigid Manifold
We describe the mirror of the Z orbifold as a representation of a class of
generalized Calabi-Yau manifolds that can be realized as manifolds of dimension
five and seven. Despite their dimension these correspond to superconformal
theories with and so are perfectly good for compactifying the heterotic
string to the four dimensions of space-time. As a check of mirror symmetry we
compute the structure of the space of complex structures of the mirror and
check that this reproduces the known results for the Yukawa couplings and
metric appropriate to the Kahler class parameters on the Z orbifold together
with their instanton corrections.Comment: 39 pages, plain Te
Impact of minority concentration on fundamental (H)D ICRF heating performance in JET-ILW
ITER will start its operation with non-activated hydrogen and helium plasmas at a reduced magnetic field of B-0 = 2.65 T. In hydrogen plasmas, the two ion cyclotron resonance frequency (ICRF) heating schemes available for central plasma heating (fundamental H majority and 2nd harmonic He-3 minority ICRF heating) are likely to suffer from relatively low RF wave absorption, as suggested by numerical modelling and confirmed by previous JET experiments conducted in conditions similar to those expected in ITER's initial phase. With He-4 plasmas, the commonly adopted fundamental H minority heating scheme will be used and its performance is expected to be much better. However, one important question that remains to be answered is whether increased levels of hydrogen (due to e. g. H pellet injection) jeopardize the high performance usually observed with this heating scheme, in particular in a full-metal environment. Recent JET experiments performed with the ITER-likewall shed some light onto this question and the main results concerning ICRF heating performance in L-mode discharges are summarized here
Scattering of Cosmic Rays by Magnetohydrodynamic Interstellar Turbulence
Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for substantial revisions in our understanding of cosmic ray transport. In this
paper we use gyroresonance recently obtained scaling laws for MHD modes to
calculate the scattering frequency for cosmic rays in the ISM. We consider
gyroresonance with MHD modes (Alfvenic, slow and fast) and transit-time damping
(TTD) by fast modes. We conclude that the gyroresonance with fast modes is the
dominant contribution to cosmic ray scattering for the typical interstellar
conditions. In contrast to earlier studies, we find that Alfvenic and slow
modes are inefficient because they are far from isotropy usually assumed.Comment: 4 pages, 2 figures, Phys. Rev. Lett. in press, minor change
Heterotic/type I duality, D-instantons and an N=2 AdS/CFT correspondence
D-instanton effects are studied for the IIB orientifold T^2/I\Omega(-1)^{F_L}
of Sen using type I/heterotic duality. An exact one loop threshold calculation
of t_8 \tr F^4 and t_8(\tr F^2)^2 terms for the heterotic string on T^2 with
Wilson lines breaking SO(32) to SO(8)^4 is related to D-instanton induced terms
in the worldvolume of D7 branes in the orientifold. Introducing D3 branes and
using the AdS/CFT correspondence in this case, these terms are used to
calculate Yang-Mills instanton contributions to four point functions of the
large N_c limit of N=2 USp(2N_c) SYM with four fundamental and one
antisymmetric tensor hypermultiplets.Comment: 25 pages, harvmac(b), one figure, v2: minor changes, version to
appear in PR
Infrared Exponents and the Running Coupling of Landau gauge QCD and their Relation to Confinement
The infrared behaviour of the gluon and ghost propagators in Landau gauge QCD
is reviewed. The Kugo-Ojima confinement criterion and the Gribov-Zwanziger
horizon condition result from quite general properties of the ghost
Dyson-Schwinger equation. The numerical solutions for the gluon and ghost
propagators obtained from a truncated set of Dyson-Schwinger equations provide
an explicit example for the anticipated infrared behaviour. The results are in
good agreement with corresponding lattice data obtained recently. The resulting
running coupling approaches a fix point in the infrared, . Two different fits for the scale dependence of the running coupling
are given and discussed.Comment: 3 pages, 3 figures; talk given by R.A. at the conference Quark
Nuclear Physics 200
New Symmetries of Supersymmetric Effective Lagrangians
We consider the structure of effective lagrangians describing the low-energy
dynamics of supersymmetric theories in which a global symmetry is
spontaneously broken to a subgroup while supersymmetry is unbroken. In
accordance with the supersymmetric Goldstone theorem, these lagrangians contain
Nambu--Goldstone superfields associated with a coset space ,
where is the complexification of and is the largest
subgroup of that leaves the order parameter invariant. The lagrangian may
also contain additional light matter fields. To analyze the effective
lagrangian for the matter fields, we first consider the case where the
effective lagrangian is obtained by integrating out heavy modes at weak
coupling (but including non-perturbative effects such as instantons). We show
that the superpotential of the matter fields is invariant, which can
give rise to non-trivial relations among independent -invariants in the
superpotential. We also show that the Kahler potential of the matter fields can
be restricted by a remnant of symmetry. These results are
non-perturbative and have a simple group-theoretic interpretation. When we
relax the weak-coupling constraint, there appear to be additional possibilities
for the action of on the matter fields, hinting that the constraints
imposed by may be even richer in strongly coupled theories.Comment: 23 pages, plain Te
Higher Loop Spin Field Correlators in D=4 Superstring Theory
We develop calculational tools to determine higher loop superstring
correlators involving massless fermionic and spin fields in four space time
dimensions. These correlation functions are basic ingredients for the
calculation of loop amplitudes involving both bosons and fermions in D=4
heterotic and superstring theories. To obtain the full amplitudes in Lorentz
covariant form the loop correlators of fermionic and spin fields have to be
expressed in terms of SO(1,3) tensors. This is one of the main achievements in
this work.Comment: 59 pages, 1 figure; v2: final version published in JHE
Quantum cohomology of partial flag manifolds
We compute the quantum cohomology rings of the partial flag manifolds
F_{n_1\cdots n_k}=U(n)/(U(n_1)\times \cdots \times U(n_k)). The inductive
computation uses the idea of Givental and Kim. Also we define a notion of the
vertical quantum cohomology ring of the algebraic bundle. For the flag bundle
F_{n_1\cdots n_k}(E) associated with the vector bundle E this ring is found.Comment: 33 page
Quantization of the N=2 Supersymmetric KdV Hierarchy
We continue the study of the quantization of supersymmetric integrable KdV
hierarchies. We consider the N=2 KdV model based on the affine
algebra but with a new algebraic construction for the L-operator, different
from the standard Drinfeld-Sokolov reduction. We construct the quantum
monodromy matrix satisfying a special version of the reflection equation and
show that in the classical limit, this object gives the monodromy matrix of N=2
supersymmetric KdV system. We also show that at both the classical and the
quantum levels, the trace of the monodromy matrix (transfer matrix) is
invariant under two supersymmetry transformations and the zero mode of the
associated U(1) current.Comment: LaTeX2e, 12 page
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