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QED processes at electron-positron colliders are considerd. We present differential cross-sections for large--angle Bhabha scattering, annihilation into muons and photons. Radiative corrections in the first order are taken into account exactly. Leading logarithmic contributions are calculated in all orders by means of the structure-function method. An accuracy of the calculation can be estimated about 0.2%. [ABSTRACT FROM AUTHOR]

We study some aspects of the strong coupling dynamics of Dirichlet six branes, anti- six branes, and orientifold planes by using the equivalence of type IIA string theory and M-theory on S1. In the strong coupling limit there exists static configuration of brane and anti-brane at arbitrary separation, suspended in an external magnetic field. The mass of the open string stretched between the brane and the anti-brane approaches a finite positive value even when the branes coincide. Similar result is obtained for a Dirichlet six brane on top of an orientifold six plane. We also derive the anomalous gravitational interaction on the brane and the orientifold plane from M-theory. [ABSTRACT FROM AUTHOR]

We continue our study of heterotic/type-I duality in D < 10 dimensions. We consider the heterotic and type-I theories compactified on tori to lower dimensions. We calculate the special (``BPS-saturated'') ℱ4 and ℛ4 terms in the effective one-loop heterotic action. These terms are expected to be non-perturbatively exact for D > 4. The heterotic result is compared with the associated type-I result. In D < 9 dimensions, the type-I theory has instanton corrections due to D1 instantons. In D = 8 we use heterotic/type-I duality to give a simple prescription of the D-instanton calculation on the type-I side. We allow arbitrary Wilson lines and show that the D1-instanton determinant is the affine character-valued elliptic genus evaluated at the induced complex structure of the D1-brane world-volume. The instanton result has an expansion in terms of Hecke operators that suggests an interpretation in terms of an SO(N) matrix model of the D1-brane. The total result can be written in terms of generalized prepotentials, revealing an underlying holomorphic structure. In D < 8 we calculate again the heterotic perturbative thresholds and show that they agree with the D1-instanton calculation using the rules derived in D = 8. [ABSTRACT FROM AUTHOR]

We show that QCD observables defined as infrared- and collinear-safe, according to the usual Sterman-Weinberg criteria, can nevertheless be infinite at accessible points inside phase space, to any finite order of perturbation theory. Infrared finiteness is restored after resummation of divergent terms to all orders. The resulting characteristic structure, which we call a Sudakov shoulder, represents an interesting new class of QCD predictions. [ABSTRACT FROM AUTHOR]

Processes of electron--positron annihilation into charged pions and kaons are considered. Radiative corrections are taken into account exactly in the first order and within the leading logarithmic approximation in higher orders. A combined approach for accounting exact calculations and electron structure functions is used. An accuracy of the calculation can be estimated about 0.2%. [ABSTRACT FROM AUTHOR]

If the gravitino is light and all the other supersymmetric particles are heavy, we can consider the effective theory describing the interactions of its goldstino components with ordinary matter. To discuss the model-dependence of these interactions, we take the simple case of spontaneously broken supersymmetry and only two chiral superfields, associated with the goldstino and a massless matter fermion. We derive the four-point effective coupling involving two matter fermions and two goldstinos, by explicit integration of the heavy spin-0 degrees of freedom in the low-energy limit. Surprisingly, our result is not equivalent to the usual non-linear realization of supersymmetry, where a pair of goldstinos couples to the energy-momentum tensor of the matter fields. We solve the puzzle by enlarging the non-linear realization to include a second independent invariant coupling, and we show that there are no other independent couplings of this type up to this order in the low-energy expansion. We conclude by commenting on the interpretation of our results and on their possible phenomenological implications. [ABSTRACT FROM AUTHOR]

We discuss the relation between the Ramond-Ramond charges of D-branes and the topology of Chan-Paton vector bundles. We show that a topologically nontrivial normal bundle induces RR charge and that the result fits in perfectly with the proposal that D-brane charge is the topology of the Chan-Paton bundle, regarded as an element of K-theory. [ABSTRACT FROM AUTHOR]

We show how certain non-perturbative superpotentials W̃(Σ), which are the two-dimensional analogs of the Seiberg-Witten prepotential in 4d, can be computed via geometric engineering from 4-folds. We analyze an explicit example for which the relevant compact geometry of the 4-fold is given by ℙ1 fibered over ℙ2. In the field theory limit, this gives an effective U(1) gauge theory with N = (2,2) supersymmetry in two dimensions. We find that the analog of the SW curve is a K3 surface, and that the complex FI coupling is given by the modular parameter of this surface. The FI potential itself coincides with the middle period of a meromorphic differential. However, it only shows up in the effective action if a certain 4-flux is switched on, and then supersymmetry appears to be non-perturbatively broken. This can be avoided by tuning the bare FI coupling by hand, in which case the supersymmetric minimum naturally corresponds to a singular K3. [ABSTRACT FROM AUTHOR]

Covariant field equations of M-fivebrane in eleven dimensional curved superspace are obtained from the requirement of κ-symmetry of an open supermembrane ending on a fivebrane. The worldvolume of the latter is a (6|16) dimensional supermanifold embedded in the (11|32) dimensional target superspace. The κ-symmetry of the system imposes a constraint on this embedding, and a constraint on a modified super 3-form field strength on the fivebrane worldvolume. These constraints govern the dynamics of the M-fivebrane. [ABSTRACT FROM AUTHOR]

Extremal black holes in M-theory compactification on M × S1 are microscopically represented by fivebranes wrapping P × S1, where M is a Calabi-Yau threefold and P is a four-cycle in M. Additional spacetime charges arise from momentum around the S1 and expectation values for the self-dual three-form field strength in the fivebrane. The microscopic entropy of the fivebrane as a function of all the charges is determined from a two-dimensional (0,4) sigma model whose target space includes the fivebrane moduli space. This entropy is compared to the macroscopic formula. Precise agreement is found for both the tree-level and one-loop expressions. [ABSTRACT FROM AUTHOR]

We consider a one-brane probe in the presence of a five-dimensional black hole in the classical limit. The velocity-dependent force on a slowly-moving probe is characterized by a metric on the probe moduli space. This metric is computed for large black holes using low-energy supergravity, and for small black holes using D-brane gauge theory. The results are compared. [ABSTRACT FROM AUTHOR]

We propose a nonperturbative definition of heterotic string theory on arbitrary multidimensional tori. [ABSTRACT FROM AUTHOR]

We construct two quantum spin chains hamiltonians with quantum sl(2|1) invariance. These spin chains define variants of the Hubbard model and describe electron models with pair hoppings. A cubic algebra that admits the Birman-Wenzl-Murakami algebra as a quotient allows exact solvability of the periodic chain. The two hamiltonians, respectively built using the distinguished and the fermionic bases of 풰q(sl(2|1)) differ only in the boundary terms. They are actually equivalent, but the equivalence is non local. Reflection equations are solved to get exact solvability on open chains with non trivial boundary conditions. Two families of diagonal solutions are found. The centre and the scasimirs of the quantum enveloping algebra of sl(2|1) appear as tools for the construction of exactly solvable hamiltonians. [ABSTRACT FROM AUTHOR]

We discuss several mechanisms to cancel the anomalies of a 5-brane embedded in M-theory. Two of them work, provided we impose suitable conditions either on the 11-dimensional manifold of M-theory or on the 4-form field strength of M-theory. [ABSTRACT FROM AUTHOR]

More general constructions are given of six-dimensional theories that look at low energy like six-dimensional super Yang-Mills theory. The constructions start with either parallel fivebranes in Type IIB, or M-theory on (ℂ2 × S1)/Γ for Γ a suitable finite group. Via these constructions, one can obtain six-dimensional theories with any simple gauge group, and SU(r) theories with any rational theta angle. A matrix construction of these theories is also possible. [ABSTRACT FROM AUTHOR]

The worldvolume field equations of M-branes and D-branes are known to admit p-brane soliton solutions. These solitons are shown to saturate a BPS-type bound on their p-volume tensions, which are expressed in terms of central charges that are expected to appear in the worldvolume supertranslation algebra. The cases we consider include vortices, `BIons', instantons and dyons (both abelian and non-abelian), and the string boundaries of M-2-branes in the M-5-brane. [ABSTRACT FROM AUTHOR]

Within two specific string cosmology scenarios - differing in the way the pre- and post-big bang phases are joined - we compute the size and spectral slope of various types of cosmologically amplified quantum fluctuations that arise in generic compactifications of heterotic string theory. By further imposing that these perturbations become the dominant source of energy at the onset of the radiation era, we obtain physical bounds on the background's moduli, and discuss the conditions under which both a (quasi-) scale-invariant spectrum of axionic perturbations and sufficiently large seeds for the galactic magnetic fields are generated. We also point out a potential problem with achieving the exit to the radiation era when the string coupling is near its present value. [ABSTRACT FROM AUTHOR]

A connection is made between the Witten index of relevance to threshold bound states of D-particles in the type IIA superstring theory and the measure that enters D-instanton sums for processes dominated by single multiply-charged D-instantons in the type IIB theory. [ABSTRACT FROM AUTHOR]

The low-energy supersymmetric quantum mechanics describing D-particles in the background of D8-branes and orientifold planes is analyzed in detail, including a careful discussion of Gauss' law and normal ordering of operators. This elucidates the mechanism that binds D-particles to an orientifold plane, in accordance with the predictions of heterotic/type I duality. The ocurrence of enhanced symmetries associated with massless bound states of a D-particle with one orientifold plane is illustrated by the enhancement of SO(14) × U(1) to E8 and SO(12) × U(1) to E7 at strong type I' coupling. Enhancement to higher-rank groups involves both orientifold planes. For example, the enhanced E8 × E8 × SU(2) symmetry at the self-dual radius of the heterotic string is seen as the result of two D8-branes coinciding midway between the orientifold planes, while the enhanced SU(18) symmetry results from the coincidence of all sixteen D8-branes and SO(34) when they also coincide with an orientifold plane. As a separate by-product, the s-rule of brane-engineered gauge theories is derived by relating it through a chain of dualities to the Pauli exclusion principle. [ABSTRACT FROM AUTHOR]

We describe various approaches that give matrix descriptions of compactified NS five-branes. As a result, we obtain matrix models for Yang-Mills theories with sixteen supersymmetries in dimensions 2,3,4 and 5. The equivalence of the various approaches relates the Coulomb branch of certain gauge theories to the moduli space of instantons on T4. We also obtain an equivalence between certain six-dimensional string theories. Further, we discuss how various perturbative and non-perturbative features of these Yang-Mills theories appear in their matrix formulations. The matrix model for four-dimensional Yang-Mills is manifestly S-dual. In this case, we describe how electric fluxes, magnetic fluxes and the interaction between vector particles are realized in the matrix model. [ABSTRACT FROM AUTHOR]

We present a crude Matrix Theory model for Schwarzschild black holes in uncompactified dimension greater than 5. The model accounts for the size, entropy, and long range static interactions of black holes. The key feature of the model is a Boltzmann gas of D0 branes, a concept which depends on certain qualitative features of Matrix Theory which have not previously been utilized in studies of black holes. [ABSTRACT FROM AUTHOR]

Based on a gas picture of D0-brane partons, it is shown that the entropy, as well as the geometric size of an infinitely boosted Schwarzschild black hole, can be accounted for in matrix theory by interactions involving spins, or interactions involving more than two bodies simultaneously. [ABSTRACT FROM AUTHOR]

We consider a system of D0-branes in toroidally compactified space with interactions described by a Born-Infeld-type generalisation of the leading v2+v4/rD−4 terms (D is the number of non-compact directions in M-theory, including the longitudinal one). This non-linear action can be interpreted as an all-loop large N super Yang-Mills effective action and has a remarkable scaling property. We first study the classical dynamics of a brane probe in the field of a central brane source and observe the interesting difference between the D = 5 and D > 5 cases: for D > 5 the center acts as a completely absorbing black hole of effective size proportional to a power of the probe energy, while for D = 5 there is no absorption for any impact parameter. A similar dependence on D is found in the behaviour of the Boltzmann partition function Z of an ensemble of D0-branes. For D = 5 (i.e. for compactification on 6-torus) Z is convergent at short distances and is analogous to the ideal gas one. For D > 5 the system has short-distance instability. For sufficiently low temperature Z is shown to describe the thermodynamics of a Schwarzschild black hole in D > 5 dimensions, supporting recent discussions of black holes in Matrix theory. [ABSTRACT FROM AUTHOR]

The perturbative all-order analysis of the jet-broadening B-distribution in the small-B region is carried out with single-logarithmic accuracy, which requires the control of both the sum of the moduli and the modulus of the sum of the transverse momenta of soft gluons. We confirm the master equation for the B-distribution derived by Catani, Turnock and Webber (CTW). Proper treatment of quark recoil is necessary at this accuracy. This effect was neglected in the CTW solution. We show that the answer can be expressed in terms of the CTW result but evaluated at a properly rescaled B value. [ABSTRACT FROM AUTHOR]

We show how to obtain a ``heavy'' meson effective lagrangian for the case where the number of heavy particles is not conserved. We apply the method in a simple example at tree level and perform then the reduction for the case of vector mesons in Chiral Perturbation Theory in a manifestly chiral invariant fashion. Some examples showing that ``heavy'' meson effective theory also reproduces the correct non-analytical terms at the one-loop level are included. [ABSTRACT FROM AUTHOR]

We calculate the cross section for s-wave neutralino annihilation to three-body final states below the W+W− and tt̄ thresholds. Such three-body channels may dominate the annihilation cross section if the neutralino mass is not too much less than mt and mW respectively. Furthermore, because neutrinos produced in these channels are much more energetic than those from the bb̄ or τ+τ− channels, they can dominate the energetic-neutrino fluxes from neutralino annihilation in the Sun or Earth far below these thresholds and significantly enhance the neutrino signal in certain regions of the supersymmetric parameter space. [ABSTRACT FROM AUTHOR]

Supersymmetric N = 1, D = 4 string vacua are known to be finite in perturbation theory. However, the effective low energy D = 4, N = 1 field theory lagrangian does not yield, in general, finite theories. In this note we present the first (to our knowledge) such example. It may be constructed in three dual ways: i) as a Z3 , SO(32) heterotic orbifold; ii) as a type-IIB, Z3 orientifold with only ninebranes and a Wilson line, or iii) as a type-IIB , Z6 orientifold with only fivebranes. The gauge group is SU(4)3 with three chiral generations. Although chiral, a subsector of the model is continously connected to a model with globalN = 4 supersymmetry. From the Z6, type IIB orientifold point of view the above connection may be understood as a transition of four dynamical fivebranes from a fixed point to the bulk. The N = 1 model is, thus, also expected to be S-dual. We also remark that, using the untwisted dilaton and moduli fields of these constructions as spurion fields, soft SUSY-breaking terms which preserve finiteness even for N = 0 are yielded. [ABSTRACT FROM AUTHOR]

The point where a D2-brane intersecting a stack of D2-branes is proposed as a candidate for the 't Hooft vortex in the world-volume theory of N D2-branes. This straightforwardly generalizes to D3-branes, where a vortex line is generated by the intersection. Similarly, there are such objects on M-branes. We use Maldacena's conjecture to compute the static potential between a vortex and an anti-vortex in each case, in the large N limit. [ABSTRACT FROM AUTHOR]

This is the first of a series of papers devoted to the group-theoretical analysis of the conditions which must be satisfied for a configuration of intersecting M5-branes to be supersymmetric. In this paper we treat the case of static branes. We start by associating (a maximal torus of) a different subgroup of Spin10 with each of the equivalence classes of supersymmetric configurations of two M5-branes at angles found by Ohta and Townsend. We then consider configurations of more than two intersecting branes. Such a configuration will be supersymmetric if and only if the branes are G-related, where G is a subgroup of Spin10 contained in the isotropy of a spinor. For each such group we determine (a lower bound for) the fraction of the supersymmetry which is preserved. We give examples of configurations consisting of an arbitrary number of non-coincident intersecting fivebranes with fractions: 1/32, 1/16, 3/32, 1/8, 5/32, 3/16, and 1/4, and we determine the resulting (calibrated) geometry. [ABSTRACT FROM AUTHOR]

We complete the classification of supersymmetric configurations of two M5-branes, started by Ohta and Townsend. The novel configurations not considered before are those in which the two branes are moving relative to one another. These configurations are obtained by starting with two coincident branes and Lorentz-transforming one of them while preserving some supersymmetry. We completely classify the supersymmetric configurations involving two M5-branes, and interpret them group-theoretically. We also present some partial results on supersymmetric configurations involving an arbitrary number of M5-branes. We show that these configurations correspond to Cayley planes in eight-dimensions which are null-rotated relative to each other in the remaining (2+1) dimensions. The generic configuration preserves 1/32 of the supersymmetry, but other fractions (up to 1/4) are possible by restricting the planes to certain subsets of the Cayley grassmannian. We discuss some examples with larger fractions as well as their associated geometries. [ABSTRACT FROM AUTHOR]

In the mapping from four-dimensional gauge theories to string theory in AdS space, many features of gauge theory can be described by branes wrapped in different ways on S5, RP5, or subspaces therefore. These include a baryon vertex coupling N external charges in the fundamental representation of SU(N), a bound state of k gluons in SO(2k) gauge theory, strings coupled to external charges in the spinor representation of the gauge group, and domain walls across which the low energy gauge group changes. [ABSTRACT FROM AUTHOR]

Solving the QCD renormalization group equation at the 2-loop and 3-loop orders we obtain explicit expressions for the coupling as a function of the scale in terms of the Lambert W function. We study the nature of the ``Landau singularities'' in the complex Q2 plane and show that perturbative freezing can lead, in certain cases, to an analyticity structure that is consistent with causality. We analyze the Analytic Perturbation Theory (APT) approach which is intended to remove the ``Landau singularities'', and show that at 2-loops it is uniquely defined in terms of the Lambert W function, and that, depending on the value of the first two β function coefficients β0 and β1, it is either consistent with perturbative freezing (for β1 < −β02) with an infrared limit of −β0/β1 or leads to a non-perturbative infrared coupling with a limit of 1/β0 (for β1 > −β02). The possibility of a causal perturbative coupling is in accordance with the idea that a purely perturbative Banks-Zaks phase with an infrared fixed-point exists in QCD if the number of flavours (Nf) is increased. The causality condition implies that the perturbative phase is realized for Nf ≥ 10. [ABSTRACT FROM AUTHOR]

Experiments at CEBAF will scan the intermediate-energy region of the QCD dynamics for the nucleon form factors and for Compton Scattering. These experiments will definitely clarify the role of resummed perturbation theory and of quark-hadron duality (QCD sum rules) in this regime. With this perspective in mind, we review the factorization theorem of perturbative QCD for exclusive processes at intermediate energy scales, which embodies the transverse degrees of freedom of a parton and the Sudakov resummation of the corresponding large logarithms. We concentrate on the pion and proton electromagnetic form factors and on pion Compton scattering. New ingredients, such as the evolution of the pion wave function and the complete two-loop expression of the Sudakov factor, are included. The sensitivity of our predictions to the infrared cutoff for the Sudakov evolution is discussed. We also elaborate on QCD sum rule methods for Compton Scattering, which provide an alternative description of this process. We show that, by comparing the local duality analysis to resummed perturbation theory, it is possible to describe the transition of exclusive processes to perturbative QCD. [ABSTRACT FROM AUTHOR]

The non-commutative algebra which defines the theory of zero-branes on T4/Z2 allows a unified description of moduli spaces associated with zero-branes, two-branes and four-branes on the orbifold space. Bundles on a dual space T̂4/Z2 play an important role in this description. We discuss these moduli spaces in the context of dualities of K3 compactifications, and in terms of properties of instantons on T4. Zero-branes on the degenerate limits of the compact orbifold lead to fixed points with six-dimensional scale but not conformal invariance. We identify some of these in terms of the ADS dual of the (0,2) theory at large N, giving evidence for an interesting picture of ``where the branes live'' in ADS. [ABSTRACT FROM AUTHOR]

We demonstrate how some problems arising in simplicial quantum gravity can be successfully addressed within the framework of combinatorial group theory. In particular, we argue that the number of simplicial 3-manifolds having a fixed homology type grows exponentially with the number of tetrahedra they are made of. We propose a model of 3D gravity interacting with scalar fermions, some restriction of which gives the 2-dimensional self-avoiding-loop-gas matrix model. We propose a qualitative picture of the phase structure of 3D simplicial gravity compatible with the numerical experiments and available analytical results. [ABSTRACT FROM AUTHOR]

We study brane configurations in the presence of orientifold six-planes. After deriving the curves for 풩 = 2 supersymmetric SU(Nc) gauge theories with one flavor in the symmetric or antisymmetric representation and Nf fundamental flavors, we rotate the brane configuration, reducing the supersymmetry to 풩 = 1. For the case of an antisymmetric flavor and less than two fundamental flavors, nonperturbative effects lead to a brane configuration that is topologically a torus. Using the description of the orientifold six-planes as Dn singularities we discuss the Higgs branches for 풩 = 2 brane configurations with Sp/SO gauge groups and the related 풩 = 1 theories with tensor representations. [ABSTRACT FROM AUTHOR]

We consider the F-theory description of non-simply-connected gauge groups appearing in the E8 × E8 heterotic string. The analysis is closely tied to the arithmetic of torsion points on an elliptic curve. The general form of the corresponding elliptic fibration is given for all finite subgroups of E8 which are applicable in this context. We also study the closely-related question of point-like instantons on a K3 surface whose holonomy is a finite group. As an example we consider the case of the heterotic string on a K3 surface having the E8 gauge symmetry broken to SU(9)/ℤ3 or (E6 × SU(3))/ℤ3 by point-like instantons with ℤ3 holonomy. [ABSTRACT FROM AUTHOR]

We consider field theories arising from a large number of D3-branes near singularities in F-theory. We study the theories at various conformal points, and compute, using their conjectured string theory duals, their large N spectrum of chiral primary operators. This includes, as expected, operators of fractional conformal dimensions for the theory at Argyres-Douglas points. Additional operators, which are charged under the (sometimes exceptional) global symmetries of these theories, come from the 7-branes. In the case of a D4 singularity we compare our results with field theory and find agreement for large N. Finally, we consider deformations away from the conformal points, which involve finding new supergravity solutions for the geometry produced by the 3-branes in the 7-brane background. We also discuss 3-branes in a general background. [ABSTRACT FROM AUTHOR]

We discuss quotients of Anti-de Sitter (AdS) spacetime by a discrete group in light of the AdS-CFT correspondence. Some quotients describe closed universes which expand from zero volume to a maximum size and then contract. Maldacena's conjecture suggests that they should be represented in string theory by suitable quotients of the boundary conformal field theory. We discuss the required identifications, and construct the states associated with the linearized supergravity modes in the cosmological background. [ABSTRACT FROM AUTHOR]

An exact solution for a nonrotating boson star in (2+1) dimensional gravity with a negative cosmological constant is found. The relations among mass, particle number, and radius of the (2+1) dimensional boson star are shown. [ABSTRACT FROM AUTHOR]

A generalized spinor structure is constructed as a GL(2,ℂ) principal fiber bundle over the metric-affine manifold. Relations between vectors and spinors are established explicitly through the generalized Pauli and Dirac matrices. An expression for generalized spinor connection is obtained. The Dirac equation in metric-affine space-time is written in the form representing an interaction of spinors with nonmetricity explicitly. A possible physical meaning of nonmetrical objects is discussed in brief. [ABSTRACT FROM AUTHOR]

We present a manifestly Lorentz invariant and supersymmetric component field action for D = 10, type IIB supergravity, using a newly developed method for the construction of actions with chiral bosons, which implies only a single scalar non propagating auxiliary field. With the same method we construct also an action in which the complex two-form gauge potential and its Hodge-dual, a complex six-form gauge potential, appear in a symmetric way in compatibility with supersymmetry and Lorentz invariance. The duals of the two physical scalars of the theory turn out to be described by a SL(2,ℝ) triplet of eight-forms whose curvatures are constrained by a single linear relation. We present also a supersymmetric action in which the basic fields and their duals, six-form and eight-form potentials, appear in a symmetric way. All these actions are manifestly invariant under the global SL(2,ℝ)-duality group of D = 10, IIB supergravity and are equivalent to each other in that their dynamics corresponds to the well known equations of motion of D = 10, IIB supergravity. [ABSTRACT FROM AUTHOR]

It is shown that the BPS spectrum of Super-Yang-Mills theory on Td × ℝ, which fits into representations of the U-duality group for M-theory compactified on Td, in accordance with the matrix-theory conjecture, in fact fits into representations of the U-duality group for M-theory on Td+1, with the extra dualities realised as generalised Nahm transformations. The spectrum of BPS M-branes is analysed, new branes are discussed and matrix theory applications described. [ABSTRACT FROM AUTHOR]

The NLL corrections to the BFKL kernel are known to be very large, to the extent that even for small values of αs, they lead to physical cross sections which are not positive definite. It is shown in the context of a toy model, that such pathological behaviour is an artifact of the truncation at NLL order, and is associated in particular with double transverse logarithms. These are resummed in a manner consistent with the full NLL kernel, and are shown to change its properties quite considerably. [ABSTRACT FROM AUTHOR]

T-Duality on a timelike circle does not interchange IIA and IIB string theories, but takes the IIA theory to a type IIB* theory and the IIB theory to a type IIA* theory. The type II* theories admit E-branes, which are the images of the type II D-branes under timelike T-duality and correspond to imposing Dirichlet boundary conditions in time as well as some of the spatial directions. The effective action describing an En-brane is the n-dimensional Euclidean super-Yang-Mills theory obtained by dimensionally reducing 9+1 dimensional super-Yang-Mills on 9−n spatial dimensions and one time dimension. The IIB* theory has a solution which is the product of 5-dimensional de Sitter space and a 5-hyperboloid, and the E4-brane corresponds to a non-singular complete solution which interpolates between this solution and flat space. This leads to a duality between the large N limit of the Euclidean 4-dimensional U(N) super-Yang-Mills theory and the IIB* string theory in de Sitter space, and both are invariant under the same de Sitter supergroup. This theory can be twisted to obtain a large N topological gauge theory and its topological string theory dual. Flat space-time appears to be an unstable vacuum for the type II* theories, but they have supersymmetric cosmological solutions. [ABSTRACT FROM AUTHOR]

In this letter we quantize a previously proposed non-local lagrangian for the classical dual electrodynamics [4], showing how it can be used to construct probability amplitudes. Our results are shown to agree with those obtained in the context of Schwinger and Zwanziger formulations, but without necessity of introducing strings. [ABSTRACT FROM AUTHOR]

We calculate the Weyl anomaly for conformal field theories that can be described via the adS/CFT correspondence. This entails regularizing the gravitational part of the corresponding supergravity action in a manner consistent with general covariance. Up to a constant, the anomaly only depends on the dimension d of the manifold on which the conformal field theory is defined. We present concrete expressions for the anomaly in the physically relevant cases d = 2,4 and 6. In d = 2 we find for the central charge c = 3l/2GN, in agreement with considerations based on the asymptotic symmetry algebra of adS3. In d = 4 the anomaly agrees precisely with that of the corresponding 풩 = 4 superconformal SU(N) gauge theory. The result in d = 6 provides new information for the (0, 2) theory, since its Weyl anomaly has not been computed previously. The anomaly in this case grows as N3, where N is the number of coincident M5 branes, and it vanishes for a Ricci-flat background. [ABSTRACT FROM AUTHOR]

We present the explicit expressions for the resummation of large-xT Sudakov effects in the transverse-energy distribution of prompt-photons produced in hadronic collisions, to next-to-leading logarithmic (NLL) accuracy. Fragmentation processes do not contribute to the Sudakov resummation at NLL level. In Mellin space, the resummed radiative factor is the product of independent radiators for each external coloured parton appearing in the Born process, times a simple factor describing the interferences between initial- and final-state soft-gluon radiation. The formulae are given in terms of Mellin moments, and can be used for phenomenological applications using standard techniques for the inverse-Mellin transforms. The calculations presented in this work, when added to the existing works on DY and DIS production, complete the theoretical ground-work necessary to carry out global fits of parton densities with a uniform NLL accuracy in the large-x region. [ABSTRACT FROM AUTHOR]

In this paper we investigate the relation between the bulk and boundary in AdS/CFT. We first discuss the relation between the Poincaré and the global vacua, and then study various probes of the bulk from the boundary theory point of view. We derive expressions for retarded propagators and note that objects in free fall look like expanding bubbles in the boundary theory. We also study several Yang-Mills theory examples where we investigate thermal screening and confinement using propagators. In the case of confinement we also calculate the profile of a flux tube and provide an alternative derivation of the tension. [ABSTRACT FROM AUTHOR]