arXiv subjects

Alok Kumar

Publications and source records attributed to Alok Kumar.

67 records · Page 4Linked to original sources

arXiv1995

Symmetries of Heterotic String Theory

We study the symmetries of the two dimensional Heterotic string theory by following the approach of Kinnersley et al for the study of stationary-axially symmetric Einstein-Maxwell equations. We identify the finite dimensional groups $G'$ and $H'$ for the Einstein-Maxwell equations. We also give the constructions for the infinite number of conserved currents and the affine $\hat{o}(8, 24)$ symmetry algebra in this formulation. The generalized Ehlers and Harrison transformations are identified and a parallel between the infinite dimensional symmetry algebra for the heterotic string case with $\hat{sl}(3, R)$ that arise in the case of Einstein-Maxwell equations is pointed out.

hep-th↗

arXiv1994

Entropy of Extremal Black Holes in Two Dimensions

Entropy for two dimensional extremal black holes is computed explicitly in a finite-space formulation of the black hole thermodynamics and is shown to be zero {\it locally}. Our results are in conformity with the recent one by Hawking et al in four dimensions.

hep-th↗

arXiv1994

Thermodynamics of Two Dimensional Black Holes

Thermodynamic relations for a class of 2D black holes are obtained corresponding to observations made from finite spatial distances. We also study the thermodynamics of the charged version of the Jackiw-Teitelboim black holes found recently by Lowe and Strominger. Our results corroborate, in appropriate limits, to those obtained previously by other methods. We also analyze the stability of these black holes thermodynamically.

hep-th↗

arXiv1994

Exact Duality and Nilpotent Gauging

We obtain new duality transformations relating some exact string backgrounds, by defining the nilpotent duality. We show that the ungauged $SL(2, R)$ WZW model transforms by its action into the three dimensional plane wave geometry. We also give the inverse transformation from the plane wave to the $SL(2, R)$ model and discuss the implications of the results.

hep-th↗

arXiv1993

Singular Limits and String Solutions

It is shown that new leading ($\al'$) as well as all-order solutions of String theory can be obtained by taking appropriate singular limits of the known solutions. We give several leading order solutions for the bosonic as well as the heterotic string. We then present all-order forms of the previously known two dimensional cosmological solutions. An all-order form for the cosmological solution in three dimensions is also predicted. The physical implications of our results are discussed.

hep-th↗

arXiv1993

Gauging of T-Duality Invariant Worldsheet String Actions

T-Duality invariant worldsheet string actions, recently written down by Schwarz and Sen, are coupled to the worldsheet gauge fields. It is shown that the integration of the dual coordinates gives the conventional, vector, axial and chiral, gauged string actions for the appropriate choice of the gauged isometries. Alternatively, the gauge field integration is shown to give a T-duality invariant action which matches with the corresponding results known earlier.

hep-th↗

arXiv1993

$O(\tilde d,\tilde d)$ Transformations and 3D Black Hole

We generalize the results of a previous paper by one of the authors to show a relationship among a class of string solutions through $O(\tilde d, \tilde d)$ transformations. The results are applied to a rotating black hole solution of three dimensional general relativity discussed recently. We extend the black hole solution to string theory and show its connection with the three dimensional black string with nonzero momentum through an $O(\tilde d, \tilde d)$ transformation of the above type.

hep-th↗

arXiv1993

A New $N = 4$ Superconformal Algebra

It is shown that the previously known $N=3$ and $N=4$ superconformal algebras can be contracted consistently by singular scaling of some of the generators. For the later case, by a contraction which depends on the central term, we obtain a new $N=4$ superconformal algebra which contains an $SU(2)\times {U(1)}^4$ Kac-Moody subalgebra and has nonzero central extension.

hep-th↗

arXiv1992

Hidden Isometry in a Chiral Gauged WZW Model

It is shown that the asymmetric chiral gauging of the WZW models give rise to consistent string backgrounds. The target space structure of the ${[{SL(2,\Re)/ {SO(1,1)}}]}_L \bigotimes {[{SL(2,\Re)/U(1)}]}_R$ model is analyzed and the presence of a hidden isometry in this background is demonstrated. A nonlinear coordinate transformation is obtained which transforms the asymmetric model to the symmetric one, analyzed recently by two of the present authors.

hep-th↗

arXiv1992

Gauged String Actions and O($\tilde{d}$, $\tilde{d}$) Transformation

An O($\tilde{d}$, $\tilde{d}$) transformation is given which relates ungauged string actions to the gauged ones for a large class of models discussed recently by Giveon and Rocek. Interestingly, the transformation is background independent and has a unique matrix representation in a given space-time dimension.

hep-th↗

arXiv1992

Target Space Structure of a Chiral Gauged Wess-Zumino-Witten Model

The background for string propagation is obtained by a chiral gauging of the $SL(2,R)$ Wess-Zumino-Witten model. It is shown explicitly that the resulting background fields satisfy the field equations of the three dimensional string effective action and the target space has curvature singularity. Close connection of our solution with the three dimensional black string is demonstrated.

hep-th↗

arXiv1991

Topological Kac-Moody Algebra and Wakimoto Representation

It is shown, using the Wakimoto representation, that the level zero SU(2) Kac-Moody conformal field theory is topological and can be obtained by twisting an N=2 superconformal theory. Expressions for the associated N=2 superconformal generators are written down and the Kac-Moody generators are shown to be BRST exact.

hep-th↗

arXiv1991

String Effective Action and Two Dimensional Charged Black Hole

Graviton-dilaton background field equations in three space-time dimensions, following from the string effective action are solved when the metric has only time dependence. By taking one of the two space dimensions as compact, our solution reproduces a recently discovered charged black hole solution in two space-time dimensions. Solutions in presence of nonvanishing three dimensional background antisymmetric tensor field are also discussed.

hep-th↗