Deformations of Closed Strings and Topological Open Membranes

We study deformations of topological closed strings. A well-known example is the perturbation of a topological closed string by itself, where the associative OPE product is deformed, and which is governed by the WDVV equations. Our main interest will be closed strings that arise as the boundary theory for topological open membranes, where the boundary string is deformed by the bulk membrane operators. The main example is the topological open membrane theory with a nonzero 3-form field in the bulk. In this case the Lie bracket of the current algebra is deformed, leading in general to a correction of the Jacobi identity. We identify these deformations in terms of deformation theory. To this end we describe the deformation of the algebraic structure of the closed string, given by the BRST operator, the associative product and the Lie bracket. Quite remarkably, we find that there are three classes of deformations for the closed string, two of which are exemplified by the WDVV theory and the topological open membrane. The third class remains largely mysterious, as we have no explicit example.Comment: 50 pages, LaTeX; V2: minor changes, 2 references added, V3: typos corrected, signs added, modified discussion on higher correlator

U-Duality of Born-Infeld on the Noncommutative Two-Torus

We discuss Born-Infeld on the noncommutative two-torus as a description of compactified string theory. We show that the resulting theory, including the fluctuations, is manifestly invariant under the T-duality group SO(2,2;Z). The BPS mass even has a full SL(3,Z)xSL(2,Z) U-duality symmetry. The direct identification of the noncommutative parameter \theta with the B-field modulus however seems to be problematic at finite volume

σ\sigma Models for Bundles on Calabi-Yau: A Proposal for Matrix String Compactifications

We describe a class of supersymmetric gauged linear sigma-model, whose target space is the infinite dimensional space of bundles on a Calabi-Yau 3- or 2-fold. This target space can be considered the configuration space of D-branes wrapped around the Calabi-Yau. We propose that this model can be used to define matrix string theory compactifications. In the infrared limit the model flows to a superconformal non-linear sigma-model whose target space is the moduli space of BPS configurations of branes on the compact space, containing the moduli space of semi-stable bundles. We argue that the bulk degrees of freedom decouple in the infrared limit if semi-stability implies stability. We study topological versions of the model on Calabi-Yau 3-folds. The resulting B-model is argued to be equivalent to the holomorphic Chern-Simons theory proposed by Witten. The A-model and half-twisted model define the quantum cohomology ring and the elliptic genus, respectively, of the moduli space of stable bundles on a Calabi-Yau 3-fold

How Well Does AdS/QCD Describe QCD?

AdS/QCD is an extra-dimensional approach to modeling hadronic physics, motivated by the AdS/CFT correspondence in string theory. AdS/QCD models are often more accurate than would have been expected at energies below a few GeV. We address the question of why these models are so successful, and respond to some of the criticisms that have been waged against these models.Comment: To appear in proceedings of Crossing the Boundaries: Gauge Dynamics at Strong Coupling (Shifmania), Minnesota, May 14-17, 2009. 12 pages, 2 eps figure

On Central Charges and Hamiltonians for 0-brane dynamics

We consider general properties of central charges of zero branes and associated duality invariants, in view of their double role, on the bulk and on the world volume (quantum-mechanical) theory. A detailed study of the BPS condition for the mass spectrum arising from toroidal compactifications is given for 1/2, 1/4 and 1/8 BPS states in any dimensions. As a byproduct, we retreive the U-duality invariant conditions on the charge (zero mode) spectrum and the orbit classification of BPS states preserving different fractions of supersymmetry. The BPS condition for 0-branes in theories with 16 supersymmetries in any dimension is also discussed.Comment: 23 pages, latex fil

An M-theory solution generating technique and SL(2,R)

In this paper we generalize the O(p+1,p+1) solution generating technique (this is a method used to deform Dp-branes by turning on a NS-NS B-field) to M-theory, in order to be able to deform M5-brane supergravity solutions directly in eleven dimensions, by turning on a non zero three form A. We find that deforming the M5-brane, in some cases, corresponds to performing certain SL(2,R) transformations of the Kahler structure parameter for the three-torus, on which the M5-brane has been compactified. We show that this new M-theory solution generating technique can be reduced to the O(p+1,p+1) solution generating technique with p=4. Further, we find that it implies that the open membrane metric and generalized noncommutativity parameter are manifestly deformation independent for electric and light-like deformations. We also generalize the O(p+1,p+1) method to the type IIA/B NS5-brane in order to be able to deform NS5-branes with RR three and two forms, respectively. In the type IIA case we use the newly obtained solution generating technique and deformation independence to derive a covariant expression for an open D2-brane coupling, relevant for OD2-theory.Comment: 24 pages, Latex. v2:Sections 3.2 and 3.3 improved. v3:Some clarifications added. Version published in JHE

Repositioning of Verrucosidin, a purported inhibitor of chaperone protein GRP78, as an inhibitor of mitochondrial electron transport chain complex I.

Verrucosidin (VCD) belongs to a group of fungal metabolites that were identified in screening programs to detect molecules that preferentially kill cancer cells under glucose-deprived conditions. Its mode of action was proposed to involve inhibition of increased GRP78 (glucose regulated protein 78) expression during hypoglycemia. Because GRP78 plays an important role in tumorigenesis, inhibitors such as VCD might harbor cancer therapeutic potential. We therefore sought to characterize VCD's anticancer activity in vitro. Triple-negative breast cancer cell lines MDA-MB-231 and MDA-MB-468 were treated with VCD under different conditions known to trigger increased expression of GRP78, and a variety of cellular processes were analyzed. We show that VCD was highly cytotoxic only under hypoglycemic conditions, but not in the presence of normal glucose levels, and VCD blocked GRP78 expression only when glycolysis was impaired (due to hypoglycemia or the presence of the glycolysis inhibitor 2-deoxyglucose), but not when GRP78 was induced by other means (hypoxia, thapsigargin, tunicamycin). However, VCD's strictly hypoglycemia-specific toxicity was not due to the inhibition of GRP78. Rather, VCD blocked mitochondrial energy production via inhibition of complex I of the electron transport chain. As a result, cellular ATP levels were quickly depleted under hypoglycemic conditions, and common cellular functions, including general protein synthesis, deteriorated and resulted in cell death. Altogether, our study identifies mitochondria as the primary target of VCD. The possibility that other purported GRP78 inhibitors (arctigenin, biguanides, deoxyverrucosidin, efrapeptin, JBIR, piericidin, prunustatin, pyrvinium, rottlerin, valinomycin, versipelostatin) might act in a similar GRP78-independent fashion will be discussed