RG-Flow, Gravity and the Cosmological Constant

We study the low energy effective action $S$ of gravity, induced by integrating out gauge and matter fields, in a general class of Randall-Sundrum type string compactification scenarios with exponential warp factors. Our method combines dimensional reduction with the holographic map between between 5-d supergravity and 4-d large $N$ field theory. Using the classical supergravity approximation, we derive a flow equation of the effective action $S$ that controls its behavior under scale transformations. We find that as a result each extremum of $S$ automatically describes a complete RG trajectory of classical solutions. This implies that, provided the cosmological constant is canceled in the high energy theory, classical flat space backgrounds naturally remain stable under the RG-flow. The mechanism responsible for this stability is that the non-zero vacuum energy generated by possible phase transitions, is absorbed by a dynamical adjustment of the contraction rate of the warp factor.Comment: 23 pages, 1 figur

Black Hole Evaporation and Quantum Gravity

In this note we consider some consequences of quantum gravity on the process of black hole evaporation. In particular, we will explain the suggestion by 't Hooft that quantum gravitational interactions effectively exclude simultaneous measurements of the Hawking radiation and of the matter falling into the black hole. The complementarity of these measurements is supported by the fact that the commutators between the corresponding observables can be shown to grow uncontrollably large. The only assumption that is needed to obtain this result is that the creation and annihilation modes of the in-falling and out-going matter act in the same Hilbert space. We further illustrate this phenomenon in the context of two-dimensional dilaton gravity.Comment: 28 pages, LaTex, uses epsf.tex, CERN-TH.7142/94, PUPT-144

Elliptic Genera of Symmetric Products and Second Quantized Strings

In this note we prove an identity that equates the elliptic genus partition function of a supersymmetric sigma model on the N-fold symmetric product $M^N/S_N$ of a manifold M to the partition function of a second quantized string theory on the space $M \times S^1$. The generating function of these elliptic genera is shown to be (almost) an automorphic form for O(3,2,Z). In the context of D-brane dynamics, this result gives a precise computation of the free energy of a gas of D-strings inside a higher-dimensional brane.Comment: 17 pages, latex, 1 figure, to appear in Commun. Math. Phy

Black Extended Objects, Naked Singularities and P-Branes

We treat the horizons of charged, dilaton black extended objects as quantum mechanical objects. We show that the S matrix for such an object can be written in terms of a p-brane-like action. The requirements of unitarity of the S matrix and positivity of the p-brane tension equivalent severely restrict the number of space-time dimensions and the allowed values of the dilaton parameter a. Generally, black objects transform at the extremal limit into p-branes.Comment: 9 pages, REVTE

Notes on Matrix and Micro Strings

We review some recent developments in the study of M-theory compactifications via Matrix theory. In particular we highlight the appearance of IIA strings and their interactions, and explain the unifying role of the M-theory five-brane for describing the spectrum of the T^5 compactification and its duality symmetries. The 5+1-dimensional micro-string theory that lives on the fivebrane world-volume takes a central place in this presentation.Comment: 27 pages, latex with espcrc2, 3 figures. References added. Some corrections at the end of section 10. Based on lectures given by H.V. at the APCTP Winter School held in Sokcho, Korea (Feb 1997) and joint lectures at Cargese Summer School (June 1997), as well as on talks given by H.V. at SUSY'97 (May 1997), and by R.D. and E.V. at STRINGS'97 (June 1997

On RG-flow and the Cosmological Constant

The AdS/CFT correspondence implies that the effective action of certain strongly coupled large $N$ gauge theories satisfy the Hamilton-Jacobi equation of 5d gravity. Using an analogy with the relativistic point particle, I construct a low energy effective action that includes the Einstein action and obeys a Callan-Symanzik-type RG-flow equation. It follows from the flow equation that under quite general conditions the Einstein equations admit a flat space-time solution, but other solutions with non-zero cosmological constant are also allowed. I discuss the geometric interpretation of this result in the context of warped compactifications.Comment: 11 pages, 1 figure, contribution to the proceedings of Strings '99, misprint correcte

Black Hole Horizons and Complementarity

We investigate the effect of gravitational back-reaction on the black hole evaporation process. The standard derivation of Hawking radiation is re-examined and extended by including gravitational interactions between the infalling matter and the outgoing radiation. We find that these interactions lead to substantial effects. In particular, as seen by an outside observer, they lead to a fast growing uncertainty in the position of the infalling matter as it approaches the horizon. We argue that this result supports the idea of black hole complementarity, which states that, in the description of the black hole system appropriate to outside observers, the region behind the horizon does not establish itself as a classical region of space-time. We also give a new formulation of this complementarity principle, which does not make any specific reference to the location of the black hole horizon.Comment: Some minor modifications in text and the title chang

Quantum Black Hole Evaporation

We investigate a recently proposed model for a full quantum description of two-dimensional black hole evaporation, in which a reflecting boundary condition is imposed in the strong coupling region. It is shown that in this model each initial state is mapped to a well-defined asymptotic out-state, provided one performs a certain projection in the gravitational zero mode sector. We find that for an incoming localized energy pulse, the corresponding out-going state contains approximately thermal radiation, in accordance with semi-classical predictions. In addition, our model allows for certain acausal strong coupling effects near the singularity, that give rise to corrections to the Hawking spectrum and restore the coherence of the out-state. To an asymptotic observer these corrections appear to originate from behind the receding apparent horizon and start to influence the out-going state long before the black hole has emitted most of its mass. Finally, by putting the system in a finite box, we are able to derive some algebraic properties of the scattering matrix and prove that the final state contains all initial information.Comment: 37 pages (figs 2 and 3 included as uuencoded compressed tar file), Latex, needs epsf.tex, PUPT-1395, IASSNS-HEP-93/25 (revised version has minor corrections, one reference added