String Theory: A Framework for Quantum Gravity and Various Applications

In this semi-technical review we discuss string theory (and all that goes by that name) as a framework for a quantum theory of gravity. This is a new paradigm in theoretical physics that goes beyond relativistic quantum field theory. We provide concrete evidence for this proposal. It leads to the resolution of the ultra-violet catastrophe of Einstein's theory of general relativity and an explanation of the Bekenstein-Hawking entropy (of a class of black holes) in terms of Boltzmann's formula for entropy in statistical mechanics. We discuss `the holographic principle' and its precise and consequential formulation in the AdS/CFT correspondence of Maldacena. One consequence of this correspondence is the ability to do strong coupling calculations in SU(N) gauge theories in terms of semi-classical gravity. In particular, we indicate a connection between dissipative fluid dynamics and the dynamics of black hole horizons. We end with a discussion of elementary particle physics and cosmology in the framework of string theory. We do not cover all aspects of string theory and its applications to diverse areas of physics and mathematics, but follow a few paths in a vast landscape of ideas. (This article has been prepared for the TWAS Silver Jubilee)Comment: 38 pages, 5 figures, Article for TWAS Jubilee Publication, References and Comments adde

Black Holes: A Window into A New Theory of Space Time

S. Chandrasekhar wrote in the prologue to his book on black holes, "The black holes of nature are the most perfect macroscopic objects there are in the universe: the only elements in their construction are our concepts of space and time." In this contribution I briefly discuss recent developments in fundamental theory and black holes that vindicate this statement in a modern perspective. I also include some of my reminiscences of Chandra.Comment: One reference correcte

Increasing women's representation in France and India

Cet article présente la question de la représentation politique des femmes en France et en Inde. Tout d’abord, il vise à mettre en évidence comment la représentation des femmes était inscrite à l’agenda politique de chaque pays. Ensuite, il propose un examen critique des arguments utilisés pour justifier la demande d’une meilleure représentation ainsi que de ceux pour s’y opposer. Enfin, il considère les conclusions que l’on peut tirer de ces deux cas. Dépassant les cadres comparatifs traditionnels utilisés par les féministes occidentales et en contestant l’insistance française sur l'idée d'une France unique, cet article identifie les particularismes et les points communs de chaque cas, pour tenter d’atteindre à ce que Shirin Rai appelle “un dépassement enraciné des frontières culturelles, historiques et politiques.” (Rai, 2000: 15)

A Time-Dependent Classical Solution of C=1 String Field Theory and Non-Perturbative Effects

We describe a real-time classical solution of $c=1$ string field theory written in terms of the phase space density, $u(p,q,t)$, of the equivalent fermion theory. The solution corresponds to tunnelling of a single fermion above the filled fermi sea and leads to amplitudes that go as \exp(- C/ \gst). We discuss how one can use this technique to describe non-perturbative effects in the Marinari-Parisi model. We also discuss implications of this type of solution for the two-dimensional black hole.Comment: 23

Stringy Quantum Effects in 2-Dimensional Black-Hole

We discuss the classical 2-dim. black-hole in the framework of the non-perturbative formulation (in terms of non-relativistic fermions) of c=1 string field theory. We identify an off-shell operator whose classical equation of motion is that of tachyon in the classical graviton-dilaton black-hole background. The black-hole `singularity' is identified with the fermi surface in the phase space of a single fermion, and as such is a consequence of the semi-classical approximation. An exact treatment reveals that stringy quantum effects wash away the classical singularity.Comment: 17p, TIFR/TH/92-63; (v3) tex error correcte