Large N Elliptic Genus and AdS/CFT Correspondence

According to one of Maldacena's dualities, type IIB string theory on AdS_3 X S^3 X K3 is equivalent to a certain N=(4,4) superconformal field theory. In this note we compute the elliptic genus of the boundary theory in the supergravity approximation. A finite quantity is obtained once we introduce a particular exclusion principle. In the regime where the supergravity approximation is reliable, we find exact agreement with the elliptic genus of a sigma model with target space K3^N/S_N.Comment: 13 pages, LaTe

Wakimoto realizations of current algebras: an explicit construction

A generalized Wakimoto realization of $\widehat{\cal G}_K$ can be associated with each parabolic subalgebra ${\cal P}=({\cal G}_0 +{\cal G}_+)$ of a simple Lie algebra ${\cal G}$ according to an earlier proposal by Feigin and Frenkel. In this paper the proposal is made explicit by developing the construction of Wakimoto realizations from a simple but unconventional viewpoint. An explicit formula is derived for the Wakimoto current first at the Poisson bracket level by Hamiltonian symmetry reduction of the WZNW model. The quantization is then performed by normal ordering the classical formula and determining the required quantum correction for it to generate $\widehat{\cal G}_K$ by means of commutators. The affine-Sugawara stress-energy tensor is verified to have the expected quadratic form in the constituents, which are symplectic bosons belonging to ${\cal G}_+$ and a current belonging to ${\cal G}_0$. The quantization requires a choice of special polynomial coordinates on the big cell of the flag manifold $P\backslash G$. The effect of this choice is investigated in detail by constructing quantum coordinate transformations. Finally, the explicit form of the screening charges for each generalized Wakimoto realization is determined, and some applications are briefly discussed.Comment: 38 pages, LaTeX, contains improved formulations of theorems 3 and 6, two references and a remark added, plus minor stylistic change

General covariance of the non-abelian DBI-action

In this paper we study the action for N D0-branes in a curved background. In particular, we focus on the meaning of space-time diffeomorphism invariance. For a single D-brane, diffeomorphism invariance acts in a naive way on the world-volume fields, but for multiple D-branes, the meaning of diffeomorphism invariance is much more obscure. The problem goes beyond the determination of an ordering of the U(N)-valued fields, because one can show that there is no lift of ordinary diffeomorphisms to matrix-valued diffeomorphisms. On the other hand, the action can presumably be constructed from perturbative string theory calculations. Based on the general characteristics of such calculations we determine a set of constraints on the action for N D0-branes, that ensure space-time covariance. These constraints can be solved order by order, but they are insufficient to determine the action completely. All solutions to the constraints obey the axioms of D-geometry. Moreover the action must contain new terms. This exhibits clearly that the answer is more than a suitable ordering of the action of a single D0 brane.Comment: latex, 38 page

An explicit construction of Wakimoto realizations of current algebras

It is known from a work of Feigin and Frenkel that a Wakimoto type, generalized free field realization of the current algebra $\widehat{\cal G}_k$ can be associated with each parabolic subalgebra ${\cal P}=({\cal G}_0+{\cal G}_+)$ of the Lie algebra ${\cal G}$, where in the standard case ${\cal G}_0$ is the Cartan and ${\cal P}$ is the Borel subalgebra. In this letter we obtain an explicit formula for the Wakimoto realization in the general case. Using Hamiltonian reduction of the WZNW model, we first derive a Poisson bracket realization of the ${\cal G}$-valued current in terms of symplectic bosons belonging to ${\cal G}_+$ and a current belonging to ${\cal G}_0$. We then quantize the formula by determining the correct normal ordering. We also show that the affine-Sugawara stress-energy tensor takes the expected quadratic form in the constituents.Comment: 13 pages, LaTeX; a typo corrected in (5.5-6), refs and a remark adde

Target Space Supersymmetric Sigma Model Calculations

We briefly review the covariant formulation of the Green-Schwarz superstring by Berkovits, and describe how a detailed tree-level and one-loop analysis of this model leads, for the first time, to a derivation of the low-energy effective action of the heterotic superstring while keeping target-space supersymmetry manifest. The resulting low-energy theory is old-minimal supergravity coupled to tensor multiplet. The dilaton is part of the compensator multiplet.Comment: LaTeX, 8 pages; to appear in proceedings of workshop on Gauge Theory, Applied Supersymmetry and Gauge Theory, Imperial College, July 5-10 199

Conformal Field Theories: From Old to New

In a short review of recent work, we discuss the general problem of constructing the actions of new conformal field theories from old conformal field theories. Such a construction follows when the old conformal field theory admits new conformal stress tensors in its chiral algebra, and it turns out that the new conformal field theory is generically a new spin-two gauge theory. As an example we discuss the new spin-two gauged sigma models which arise in this fashion from the general conformal non-linear sigma model.Comment: 7 pages, LaTeX, to appear in a memorial issue of Theoretical and Mathematical Physics in memory of F.A. Lune

Two-dimensional Conformal Field Theories on AdS_{2d+1} Backgrounds

Various exact two-dimensional conformal field theories with AdS_{2d+1} target space are constructed. These models can be solved using bosonization techniques. Some examples are presented that can be used in building perturbative superstring theories with AdS backgrounds, including AdS_5.Comment: 36 pages, harvma

Success factors for managing purchasing groups: an empirical survey

In this article, we identify success factors for managing small and intensive purchasing groups by comparing successful and unsuccessful Dutch purchasing groups in a large-scale survey. Transaction costs economics and social exchange theory are used as theoretical frameworks for our broad empirical investigation. We found that the success factors studied that are related to interorganizational trust, the formality of the group, and uniformity of the group members are not success factors for managing purchasing groups. For our data set, the most important success factors are no enforced participation, sufficient total contribution of efforts, all members contribute knowledge, all members rarely change representatives, fair allocation of savings, and communication. We discuss the academic and practical implications of the success factors found