36,526 research outputs found
Wilson-'t Hooft operators in four-dimensional gauge theories and S-duality
We study operators in four-dimensional gauge theories which are localized on
a straight line, create electric and magnetic flux, and in the UV limit break
the conformal invariance in the minimal possible way. We call them Wilson-'t
Hooft operators, since in the purely electric case they reduce to the
well-known Wilson loops, while in general they may carry 't Hooft magnetic
flux. We show that to any such operator one can associate a maximally symmetric
boundary condition for gauge fields on AdS^2\times S^2. We show that Wilson-'t
Hooft operators are classifed by a pair of weights (electric and magnetic) for
the gauge group and its magnetic dual, modulo the action of the Weyl group. If
the magnetic weight does not belong to the coroot lattice of the gauge group,
the corresponding operator is topologically nontrivial (carries nonvanishing 't
Hooft magnetic flux). We explain how the spectrum of Wilson-'t Hooft operators
transforms under the shift of the theta-angle by 2\pi. We show that, depending
on the gauge group, either SL(2,Z) or one of its congruence subgroups acts in a
natural way on the set of Wilson-'t Hooft operators. This can be regarded as
evidence for the S-duality of N=4 super-Yang-Mills theory. We also compute the
one-point function of the stress-energy tensor in the presence of a Wilson-'t
Hooft operator at weak coupling.Comment: 32 pages, latex. v2: references added. v3: numerical factors
corrected, other minor change
ROSAT Detection and High Precision Localization of X-ray Sources in the November 19, 1978 Gamma-Ray Burst Error Box
We report on observations of the 1978, November 19 Gamma-Ray Burst source,
performed with the ROSAT X-ray HRI experiment. Two sources were detected, one
of which is possibly variable. The latter source is identical to the source
discovered in 1981 by the EINSTEIN satellite, and recently detected by ASCA.
The precise localization of these sources is given, and our data are compared
with optical, radio and previous X-ray data.Comment: 10 pages with 2 figures, Accepted for publication in the
Astrophysical Journal (Letters), Latex, aastex macros neede
Single Hadronic-Spin Asymmetries in Weak Interaction Processes
We show that measurements of single-spin asymmetries (SSAs) in charged
current weak interaction processes such as deep inelastic neutrino scattering
on a polarized target and inclusive production in polarized hadron-hadron
collisions discriminate between the two fundamental QCD mechanisms (the Sivers
and Collins effects) which have been proposed to explain such time-reversal-odd
asymmetries. It has recently been shown that QCD final-state interactions due
to gluon exchange between the struck quark and the proton spectators in
semi-inclusive deep inelastic lepton scattering will produce non-zero
Sivers-type single-spin asymmetries which survive in the Bjorken limit. We show
that this QCD final-state interaction produces identical SSAs in charged and
neutral current reactions. Furthermore, the contribution of each quark to the
SSA from this mechanism is proportional to the contribution of that quark to
the polarized baryon's anomalous magnetic moment. In contrast, the Collins
effect contribution to SSAs depends on the transversity distribution of quarks
in the polarized target. Since the charged current only couples to quarks of
one chirality, it cannot sense the transversity distribution of the target, and
thus it gives no Collins-type contribution to single-spin correlations.Comment: 12 pages, 1 figur
Unification of the General Non-Linear Sigma Model and the Virasoro Master Equation
The Virasoro master equation describes a large set of conformal field
theories known as the affine-Virasoro constructions, in the operator algebra
(affine Lie algebra) of the WZW model, while the Einstein equations of the
general non-linear sigma model describe another large set of conformal field
theories. This talk summarizes recent work which unifies these two sets of
conformal field theories, together with a presumable large class of new
conformal field theories. The basic idea is to consider spin-two operators of
the form in the background of a general
sigma model. The requirement that these operators satisfy the Virasoro algebra
leads to a set of equations called the unified Einstein-Virasoro master
equation, in which the spin-two spacetime field couples to the usual
spacetime fields of the sigma model. The one-loop form of this unified system
is presented, and some of its algebraic and geometric properties are discussed.Comment: 18 pages, Latex. Talk presented by MBH at the NATO Workshop `New
Developments in Quantum Field Theory', June 14-20, 1997, Zakopane, Polan
TMD evolution and the Higgs transverse momentum distribution
The effect of the linear polarization of gluons on the transverse momentum
distribution in Higgs production is studied within the framework of TMD
factorization. For this purpose we consider the TMD evolution for general
colorless scalar boson production, from the lower mass -even scalar
quarkonium states and to the Higgs mass scale. In the
absence of an intrinsic nonperturbative linearly polarized gluon distribution
the results correspond to the CSS formalism, indicating a rather rapid decrease
with increasing energy scale. At the Higgs mass scale the contribution from
linearly polarized gluons is in this case found to be on the percent level,
somewhat larger than an earlier finding in the literature. At the lower mass
scale of quarkonium states and we find contributions at
the 15-70% level, albeit with considerable uncertainty. In the presence of an
intrinsic linear gluon polarization, percent level effects are also found at
the Higgs mass scale, but with a considerably slower evolution. Although these
results were obtained using a model for the TMDs that are approximately
Gaussian at small transverse momenta and have the correct perturbative power
law fall off at large transverse momenta, it illustrates well the differences
that can exist between results obtained from a TMD formalism as compared to a
CSS formalism. The behavior of the TMDs at small can affect the results
for all transverse momenta of the produced boson, even for a particle as heavy
as the Higgs. The TMD evolution from to may be used to
constrain the nonperturbative contributions and improve on the prediction of
the effect at the Higgs mass scale.Comment: 12 pages, 5 figures, minor additions, matches version accepted for
publication in Nuclear Physics
Unified Einstein-Virasoro Master Equation in the General Non-Linear Sigma Model
The Virasoro master equation (VME) describes the general affine-Virasoro
construction T=L^{ab}J_aJ_b+iD^a \dif J_a in the operator algebra of the WZW
model, where is the inverse inertia tensor and is the
improvement vector. In this paper, we generalize this construction to find the
general (one-loop) Virasoro construction in the operator algebra of the general
non-linear sigma model. The result is a unified Einstein-Virasoro master
equation which couples the spacetime spin-two field to the background
fields of the sigma model. For a particular solution , the unified
system reduces to the canonical stress tensors and conventional Einstein
equations of the sigma model, and the system reduces to the general
affine-Virasoro construction and the VME when the sigma model is taken to be
the WZW action. More generally, the unified system describes a space of
conformal field theories which is presumably much larger than the sum of the
general affine-Virasoro construction and the sigma model with its canonical
stress tensors. We also discuss a number of algebraic and geometrical
properties of the system, including its relation to an unsolved problem in the
theory of -structures on manifolds with torsion.Comment: LaTeX, 55 pages, one postscript figure, uses epsfig.sty. contains a
few minor corrections; version to be published in Int. J. Mod. Phys.
Cancellation of quantum mechanical higher loop contributions to the gravitational chiral anomaly
We give an explicit demonstration, using the rigorous Feynman rules developed
in~\0^{1}, that the regularized trace \tr \gamma_5 e^{-\beta \Dslash^2} for
the gravitational chiral anomaly expressed as an appropriate quantum mechanical
path integral is -independent up to two-loop level. Identities and
diagrammatic notations are developed to facilitate rapid evaluation of graphs
given by these rules.Comment: 10 pages, LaTeX and psfig (many figures
New Duality Transformations in Orbifold Theory
We find new duality transformations which allow us to construct the stress
tensors of all the twisted sectors of any orbifold A(H)/H, where A(H) is the
set of all current-algebraic conformal field theories with a finite symmetry
group H \subset Aut(g). The permutation orbifolds with H = Z_\lambda and H =
S_3 are worked out in full as illustrations but the general formalism includes
both simple and semisimple g. The motivation for this development is the
recently-discovered orbifold Virasoro master equation, whose solutions are
identified by the duality transformations as sectors of the permutation
orbifolds A(D_\lambda)/Z_\lambda.Comment: 48 pages,typos correcte
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