WZW-Toda Reduction using the Casimir Operator

We construct a quantum Hamiltonian operator for the Wess-Zumino-Witten (WZW) model in terms of the Casimir operator. This facilitates the discussion of the reduction of the WZW model to Toda field theory at the quantum level and provides a very straightforward derivation of the quantum central charge for the Toda field theory.Comment: 16pp, uses harvmac, LTH 304 (Revised version with improved discussion of non-perturbative effects

Six-loop divergences in the supersymmetric Kahler sigma model

The two-dimensional supersymmetric \s-model on a K\"ahler manifold has a non-vanishing \b-function at four loops, but the \b-function at five loops can be made to vanish by a specific choice of renormalisation scheme. We investigate whether this phenomenon persists at six loops, and conclude that it does not; there is a non-vanishing six-loop \b-function irrespective of renormalisation scheme ambiguities.Comment: 13pp, uses phyzzx, LTH 287 (published in Int. J. Mod. Phys. A

Quantum Non-abelian Toda Field Theories

We derive an explicit, exactly conformally invariant form for the action for the non-abelian Toda field theory. We demonstrate that the conformal invariance conditions, expressed in terms of the $\beta$-functions of the theory, are satisfied to all orders, and we use our results to obtain a value for the central charge agreeing with previous calculations.Comment: 28pp, harvmac (choose "b" option

Symmetries of higher-order string gravity actions

In this paper we explicitly prove the invariance of the time-dependent string gravity Lagrangian with up to four derivatives under the global $O(d,d)$ symmetry.Comment: 10 pages, LATEX file, several misprints corrected, two references added, the final version submitted to Phys.Lett.

T-Duality and Two-Loop Renormalization Flows

Manifest T-duality covariance of the one-loop renormalization group flows is shown for a generic bosonic sigma model with an abelian isometry, by referring a set of previously derived consistency conditions to the tangent space of the target. For a restricted background, T-duality transformations are then studied at the next order, and the ensuing consistency conditions are found to be satisfied by the two-loop Weyl anomaly coefficients of the model. This represents an extremely non-trivial test of the covariance of renormalization group flows under T-duality, and a stronger condition than T-duality invariance of the string background effective action.Comment: 18 pp., plain TeX + harvmac. Typos in Eqs. (4.3), (4.5) and (4.7) corrected, and references adde

Duality Transformations Away From Conformal Points

Target space duality transformations are considered for bosonic sigma models and strings away from RG fixed points. A set of consistency conditions are derived, and are seen to be nontrivially satisfied at one-loop order for arbitrary running metric, antisymmetric tensor and dilaton backgrounds. Such conditions are sufficiently stringent to enable an independent determination of the sigma model beta functions at this order.Comment: 11 pages, plain TeX. Uses harvmac.te

Higher Order Conformal Invariance of String Backgrounds Obtained by O(d,d) Transformations

Proposals that $O(d,d)$ boosts of trivial backgrounds lead to non-trivial conformally invariant backgrounds are checked to two loop order. We find that conformal invariance can be achieved by adding simple higher order corrections to the metric and dilaton.Comment: 8 page

The nonminimal scalar multiplet: duality, sigma-model, beta-function

We compute in superspace the one-loop beta-function for the nonlinear sigma-model defined in terms of the nonminimal scalar multiplet. The recently proposed quantization of this complex linear superfield, viewed as the field strength of an unconstrained gauge spinor superfield, allows to handle efficiently the infinite tower of ghosts via the Batalin-Vilkovisky formalism. We find that the classical duality of the nonminimal scalar and chiral multiplets is maintained at the quantum one-loop level.Comment: 19 pages, Latex, no figures. Few references adde

Boosting Away Singularities from Conformal String Backgrounds

Generalizing our previous work, we show how $O(d,d)$ transformations can be used to "boost away" in new dimensions the physical singularities that occur generically in cosmological and/or black-hole string backgrounds. As an example, we show how a recent model by Nappi and Witten can be made singularity-free via $O(3,3)$ boosts involving a fifth dimension.Comment: 11 pages, CERN-TH.6634/9

Macroscopic Charged Heterotic String

Classical solutions of equations of motion in low energy effective field theory, describing fundamental charged heterotic string, are found. These solutions automatically carry an electric current equal to the charge per unit length, and hence are accompanied by both, electric and magnetic fields. Force between two parallel strings vanish due to cancellation between electric and magnetic forces, and also between graviton, dilaton, and antisymmetric tensor field induced forces. Multi-string solutions describing configuration of parallel strings are also found. Finally, the solutions are shown to possess partially broken space-time supersymmetry.Comment: 20 pages, plain.te