Extensions of 2D Gravity

After reviewing some aspects of gravity in two dimensions, it is shown that non-trivial embeddings of sl(2) in a semi-simple (super) Lie algebra give rise to a very large class of extensions of 2D gravity. The induced action is constructed as a gauged WZW model and an exact expression for the effective action is given. (Talk presented at the Journees Relativistes '93, Brussels, April, 1993).Comment: 12 pages (LaTeX, 3 eps figures), LBL-34240, UCB-PTH-93/2

N = 2 world-sheet approach to D-branes on generalized Kaehler geometries: I. General formalism

We present an N = 2 world-sheet superspace description of D-branes on bihermitian or generalized Kaehler manifolds. To accomplish this, D-branes are considered as boundary conditions for a nonlinear sigma-model in what we call N = 2 boundary superspace. In this note the general formalism for such an approach is presented and the resulting classification sketched. This includes some remarks regarding target spaces whose parameterization includes semi-chiral superfields which have not appeared in the literature yet. In an accompanying note we turn to some examples and applications of the general setup presented here.Comment: 7 pages, contribution to the proceedings of the Fourth Workshop of the RTN project 'Constituents, Fundamental Forces and Symmetries of the Universe', Varna, September 11 - 17, 200

Superstrings from Hamiltonian Reduction

In any string theory there is a hidden, twisted superconformal symmetry algebra, part of which is made up by the BRST current and the anti-ghost. We investigate how this algebra can be systematically constructed for strings with $N\!-\!2$ supersymmetries, via quantum Hamiltonian reduction of the Lie superalgebras $osp(N|2)$. The motivation is to understand how one could systematically construct generalized string theories from superalgebras. We also briefly discuss the BRST algebra of the topological string, which is a doubly twisted $N\!=\!4$ superconformal algebra.Comment: 32p, LaTeX, CERN-TH.7379/9

Coset Construction and Character Sumrules for the Doubly Extended N=4N=4 Superconformal Algebras

Character sumrules associated with the realization of the $N=4$ superconformal algebra \At on manifolds corresponding to the group cosets SU(3)_{\ktp }/U(1) are derived and developed as an important tool in obtaining the modular properties of \At characters as well as information on certain extensions of that algebra. Their structure strongly suggests the existence of rational conformal field theories with central charges in the range $1 \le c\le 4$. The corresponding characters appear in the massive sector of the sumrules and are completely specified in terms of the characters for the parafermionic theory $SU(3)/(SU(2)\times U(1))$ and in terms of the branching functions of massless \At characters into SU(2)_{\ktp }\times SU(2)_1 characters.Comment: 31 pages, DTP/92/49 NBI-HE-92-73 (latex file

On the Landau-Ginzburg Realization of Topological Gravities

We study the equivariant cohomology of a class of multi-field topological LG models, and find that such systems carry intrinsic information about $W$-gravity. As a result, we can construct the gravitational chiral ring in terms of LG polynomials. We find, in particular, that the spectrum of such theories seems to be richer than so far expected. We also briefly discuss the BRST operator for non-linear topological $W$-gravity.Comment: 26p, harvmac, 4 uuencoded PostScript figure

Strings, gravity and particle physics

This contribution, aimed mostly at experimental particle physicists, reviews some of the main ideas and results of String Theory in a non-technical language. It originates from the talks presented by the authors at the Electro-Weak session of the 2002 Moriond Meeting, here merged in an attempt to provide a more complete and concise view of the subject.Comment: LaTeX, 28 pages, 13 figures. Contribution to the proceedings of the 2002 Rencontres de Moriond "Electroweak interactions and unified theories