arXiv subjects

Itzhak Bars

Publications and source records attributed to Itzhak Bars.

89 records · Page 5Linked to original sources

arXiv1996

Algebraic Structure of S-Theory

The algebraic structure of S-Theory and its representations are described. This structure includes up to 13 hidden dimensions. It implies the existence of an SO(10,2) covariant supergravity theory as a limit of the secret theory behind string theory. The black hole entropy is invariant under transformations including the 11th and 12th dimensions. The discussion includes generalization into curved spacetime via various contractions of the superalgebras OSp(1/32), OSp(1/64) etc..

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arXiv1996

S-Theory

The representation theory of the maximally extended superalgebra with 32 fermionic and 528 bosonic generators is developed in order to investigate non-perturbative properties of the democratic secret theory behind strings and other p-branes. The presence of Lorentz non-singlet central extensions is emphasized, their role for understanding up to 13 hidden dimensions and their physical interpretation as boundaries of p-branes is elucidated. The criteria for a new larger set of BPS-like non-perturbative states is given and the methods of investigation are illustrated with several explicit examples.

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arXiv1996

Duality and hidden dimensions

Using a global superalgebra with 32 fermionic and 528 bosonic charges, many features of p-brane dualities and hidden dimensions are discussed.

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arXiv1996

Supersymmetry, p-brane duality and hidden space and time dimensions

A global superalgebra with 32 supercharges and all possible central extensions is studied in order to extract some general properties of duality and hidden dimensions in a theory that treats $p$-branes democratically. The maximal number of dimensions is 12, with signature (10,2), containing one space and one time dimensions that are hidden from the point of view of perturbative 10-dimensional string theory or its compactifications. When the theory is compactified on $R^{d-1,1}\otimes T^{c+1,1}$ with $d+c+2=12,$ there are isometry groups that relate to the hidden dimensions as well as to duality. Their combined classification schemes provide some properties of non-perturbative states and their couplings.

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arXiv1996

Consistency between 11D and U-duality

U duality transformations must act on a basis of states that form complete multiplets of the U group, at any coupling, even though the states may not be mass degenerate, as for a broken symmetry. Similarly, if superstring theory is related to a non-perturbative 11D M-theory, then an 11D supermultiplet structure is expected, even though the multiplet may contain states of different masses. We analyse the consistency between these two multiplet schemes at the higher excited string levels for various compactifications of the type IIA superstring. While we find complete consistency for a number of compactifications, there remain some unanswered questions in others. The relation to D-branes also needs further clarification.

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arXiv1995

Solution of the SL(2,R) string in curved spacetime

The SL(2,R) WZW model, one of the simplest models for strings propagating in curved space time, was believed to be non-unitary in the algebraic treatment involving affine current algebra. It is shown that this was an error that resulted from neglecting a zero mode that must be included to describe the correct physics of non-compact WZW models. In the presence of the zero mode the mass-shell condition is altered and unitarity is restored. The correct currents, including the zero mode, have logarithmic cuts on the worldsheet. This has physical consequences for the spectrum because a combination of zero modes must be quantized in order to impose periodic boundary conditions on mass shell in the physical sector. To arrive at these results and to solve the model completely, the SL(2,R) WZW model is quantized in a free field formalism that differs from previous ones in that the fields and the currents are Hermitean, there are cuts, and there is a new term that could be present more generally, but is excluded in the WZW model.

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arXiv1995

U-duality multiplets and non-perturbative superstring states

We employ an algebraic approach for unifying perturbative and non-perturbative superstring states on an equal footing, in the form of U-duality multiplets, at all excited string levels. In compactified type-IIA supertring theory we present evidence that the multiplet is labelled by two spaces, ``index'' space and ``base'' space, on which U acts without mixing them. Both spaces are non-perturbative extensions of similar spaces that label perturbative T-duality multiplets. Base space consists of all the central charges of the 11D SUSY algebra, while index space corresponds to represetations of the maximal compact subgroup K in U. This structure predicts the quantum numbers of the non-perturbative states. We also discuss whether and how U-multiplets may coexist with 11-dimensional multiplets, that are associated with an additional non-perturbative 11D structure that seems to be lurking behind in the underlying theory.

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arXiv1995

Ghost-Free Spectrum of a Quantum String in SL(2,R) Curved Spacetime

The unitarity problem in curved spacetime is solved for the string described by the SL(2,R) WZW model. The spectrum is computed exactly and demonstratedto be ghost-free. The new features include (i) SL(2,R) left/right symmetrycurrents that have logarithmic cuts on the world sheet but that satisfy theusual local operator products or commutation rules, (ii) physical statesconsistent with the monodromy condition of closed strings despite thelogarithmic singularity in the currents, and (iii) a new free boson realization for these currents which render the SL(2,R) WZW model completely solvable.

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arXiv1995

STRINGY EVIDENCE FOR D=11 STRUCTURE IN STRONGLY COUPLED TYPE II-A SUPERSTRING

Witten proposed that the low energy physics of strongly coupled D=10 type-IIA superstring may be described by D=11 supergravity. To explore the stringy aspects of the underlying theory we examine the stringy massive states. We propose a systematic formula for identifying non-perturbative states in D=10 type-IIA superstring theory, such that, together with the elementary excited string states, they form D=11 supersymmetric multiplets multiplets in SO(10) representations. This provides hints for the construction of a weakly coupled D=11 theory that is dual to the strongly coupled D=10 type IIA superstring.

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arXiv1994

Folded Strings

Recent progress on the complete set of solutions of two dimensional classical string theory in any curved spacetime is reviewed. When the curvature is smooth the string solutions are deformed folded string solutions as compared to flat spacetime folded strings that were known for 19 years. However, surprizing new stringy behavior becomes evident at singularities such as black holes. The global properties of these solutions require that the ``bare singularity region"of the black hole be included along with the usual black hole spacetime. The mathematical structure needed to describe the solutions include a recursion relation that is analogous to the transfer matrix of lattice theories. This encodes lattice properties on the worldsheet on the one hand and the geometry of spacetime on the other hand. A case is made for the presence of folded strings in the quantum theory of non-critical strings for $d\geq 2$.

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arXiv1994

Classical Solutions of 2D String Theory in any Curved Spacetime

The complete set of solutions of two dimensional classical string theory are constructed for any curved spacetime. They describe folded strings moving in curved spacetime. Surprizing stringy behavior becomes evident at singularities such as black holes.The solutions are given in the form ofa map from the world sheet to target spacetime, where the world sheet has to be divided into lattice -like patches corresponding to different maps. A recursion relation analogous to a transfer matrix connects these maps into a single continuous map. This ``transfer matrix'' encodes the properties of the world sheet lattice as well as the geometry of spacetime. The solutions are completely classified by their behavior in the asymptotically flat region of spacetime where they reduce, as boundary conditions, to the folded string solutions that have been known for 19 years.

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arXiv1994

Folded Strings in Curved Spacetime

Two dimensional classical string theory is solved in any curved spacetime. The complete spacetime required to describe the classical string motions turns out to be larger than the global space required by complete particle geodesics. The solutions are fully classified by their behavior in the asymptotically flat region of spacetime. When the curvature is smooth, the string solutions are deformed folded string solutions as compared to flat spacetime folded strings that were known for 19 years. However, surprizing new stringy behavior becomes evident at curvature singularities such as black holes. The global properties of the classical string theory require that the ``bare singularity region'' of the black hole be included along with the usual black hole spacetime. The mathematical structure needed to describe the solutions include a recursion relation that is analogous to the transfer matrix of lattice theories. This encodes lattice-like properties on the worldsheet on the one hand and the geometry of spacetime on the other hand. A case is made for the presence of folded strings in the quantum theory of non-critical strings for $d\geq 2$.

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arXiv1994

Folded Strings Falling into a Black Hole

We find all the classical solutions (minimal surfaces) of open or closed strings in {\it any} two dimensional curved spacetime. As examples we consider the SL(2,R)/R two dimensional black hole, and any 4D black hole in the Schwarzschild family, provided the motion is restricted to the time-radial components. The solutions, which describe longitudinaly oscillating folded strings (radial oscillations in 4D), must be given in lattice-like patches of the worldsheet, and a transfer operation analogous to a transfer matrix determines the future evolution. Then the swallowing of a string by a black hole is analyzed. We find several new features that are not shared by particle motions. The most surprizing effect is the tunneling of the string into the bare singularity region that lies beyond the black hole that is classically forbidden to particles.

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arXiv1993

QCD and Strings in 2D

In two dimensions large N QCD with quarks, defined on the plane, is equivalent to a modified string theory with quarks at the ends and taken in the zero fold sector. The equivalence that was established in 1975 was expressed in the form of an interacting string action that reproduces the spectrum and the 1/N interactions of 2D QCD. This action may be a starting point for an analytic continuation to a four dimensional string version of QCD. After reviewing the old work I discuss relations to recent developments in the pure QCD-string equivalence on more complicated background %geometries.

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arXiv1993

Curved Spacetime Geometry for Strings and Affine Non-compact Algebras

Based on lectures delivered at (1) the AMS meeting at USC, Nov. 1992 (2) Conference on Quantum Aspects of Black Holes, ITP, UC- Santa %Barbara, %%June 1993. (3) 25th Summer Institute, Ecole Normale Superieure, % Paris, Aug. 1992. To appear in "Interface Between Mathematics and Physics", Ed. S.-T. Yau. 1--Itroduction to String Theory in Curved Spacetime 2--G/H Coset Conformal Field Theory and String Theory 3--Time, Space and Classification of Non-Compact Cosets 4--Heterotic Strings in Curved Spacetime as gauged WZW Models 5--The Spacetime Manifold and the Geometry 6--Examples in 2D, 3D and 4D

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arXiv1992

Superstrings on Curved Spacetimes

In this lecture I summarize recent developments on strings propagating in curved spacetime. Exact conformal field theories that describe gravitational backgrounds such as black holes and more intricate gravitational singularities have been discovered and investigated at the classical and quantum level. These models are described by gauged Wess-Zumino-Witten models, or equivalently current algebra G/H coset models based on non-compact groups, with a single time coordinate. The classification of such models for all dimensions is complete. Furthermore the heterotic superstrings in curved spacetime based on non-compact groups have also been constructed. For many of the $d\le 4$ models the gravitational geometry described by a sigma model has been determined. Some general results outlined here include a global analysis of the geometry and the exact classical geodesics for any G/H model. Moreover, in the quantized theory, the conformally exact metric and dilaton are obtained for all orders in an expansion of $k$ (the central extension). All such models have large-small (or mirror) duality properties which we reformulate as an inversion in group space. To illustrate model building techniques a specific 4-dimensional heterotic string in curved spacetime is presented. Finally the methods for investigating the quantum theory are outlined. The construction and analysis of these models at the classical and quantum level involve some aspects of noncompact groups which are not yet sufficiently well understood. Some of the open problems in the physics and mathematics areas are outlined.

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arXiv1992

Heterotic String Models in Curved Spacetime

We explore the possibility of string theories in only four spacetime dimensions without any additional compactified dimensions. We show that, provided the theory is defined in curved spacetime that has a cosmological interpration, it is possible to construct consistent heterotic string theories based on a few non-compact current algebra cosets. We classify these models. The gauge groups that emerge fall within a remarkably narrow range and include the desirable low energy flavor symmetry of $SU(3)\times SU(2)\times U(1)$. The quark and lepton states, which come in color triplets and $SU(2)$ doublets, are expected to emerge in several families.

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