S. P. de Alwis

Moduli potentials in string compactifications with fluxes: Mapping the discretuum

We find de Sitter and flat space solutions with all moduli stabilized in four dimensional supergravity theories derived from the heterotic and type II string theories, and explain how all the previously known obstacles to finding such solutions can be removed. Further, we argue that if the compact manifold allows a large enough space of discrete topological choices then it is possible to tune the parameters of the four dimensional supergravity such that a hierarchy is created and the solutions lie in the outer region of moduli space in which the compact volume is large in string units, the string coupling is weak, and string perturbation theory is valid. We show that at least two light chiral superfields are required for this scenario to work, however, one field is sufficient to obtain a minimum with an acceptably small and negative cosmological constant. We discuss cosmological issues of the scenario and the possible role of anthropic considerations in choosing the vacuum of the theory. We conclude that the most likely stable vacuua are in or near the central region of moduli space where string perturbation theory is not strictly valid, and that anthropic considerations cannot help much in choosing a vacuum.

Effective potentials for light moduli

Abstract We examine recent work on compactifications of string theory with fluxes, where effective potentials for light moduli have been derived after integrating out moduli that are assumed to be heavy at the classical level, and then adding non-perturbative (NP) corrections to the superpotential. We find that this two stage procedure is not valid and that the correct potential has additional terms. Althought this does not affect the conclusion of Kachru et al. (KKLT) that the Kaehler moduli may be stabilized by NP effects, it can affect the detailed physics. In particular, it is possible to get metastable dS minima without adding uplifting terms.

A note on brane tension and M-theory

Abstract We point out that some M-theory results for brane tension can be derived from Polchinskis formula for D-brane tension. We also argue that this formula determines gravitational and gauge couplings in the low energy but quantum exact effective action.

Thermodynamics of quantum fields in black hole backgrounds

We discuss the relation between the microcanonical and the canonical ensemble for black holes, and highlight some problems associated with extreme black holes already at the classical level. Then we discuss the contribution of quantum fields and demonstrate that the partition functions for scalar and Dirac (Majorana) fields in static space-time backgrounds can be expressed as functional integrals in the corresponding optical space, and point out that the difference between this and the functional integrals in the original metric is a Liouville-type action. The optical method gives both the correction to the black hole entropy and the bulk contribution to the entropy due to the radiation, while the conical singularity method just gives the divergent contribution to the black hole entropy unless one takes into account nonlocal terms. A simple derivation of a general formula for the free energy in the high-temperature approximation is given and applied to various cases. We conclude with a discussion of the second law.

Potentials from fluxes

We discuss the compactification of type IIB supergravity with fluxes to generate a potential for the moduli. In particular we resolve an apparent conflict with the no-go theorem for de Sitter space. It is shown that a positive potential for certain moduli is possible in situations where the volume modulus has no critical point. We also point out that the derivation of the potential is strictly valid only for a trivial warp factor. To go beyond that seems to require the inclusion of all the Kaluza-Klein excitations. We end with a discussion of the stabilization of the volume modulus.

Heterotic strings with tree level cosmological constant

Abstract We discuss heterotic (and super) string compactification with tree level cosmological constant. The question of having a small supersymmetry breaking is also addressed.

Quantization of a theory of 2D dilaton gravity

Abstract We discuss the quantization of the 2D gravity theory of Callan, Giddings, Harvey, and Strominger (CGHS), following the procedure of David, and of Distler and Kawai. We find that the physics depends crucially on whether the number of matter fields is greater than or less than 24. In the latter case the singularity pointed out by several authors is absent but the physical interpretation is unclear. In the former case (the one studied by CGHS) the quantum theory which gives CGHS in the linear dilaton semi-classical limit, is different from that which gives CGHS in the extreme Liouville regime.

D strings and F strings from string loops

Since the background fields of the string low energy action are supposed to be the long range manifestation of a condensate of strings, the addition of world sheet actions to the low energy effective action needs some string theoretic explanation. In this paper we suggest that this may be understood as being due to string loop effects. We first present arguments using an equation due to Tseytlin and then more rigorously in the particular case of type IIB theory by invoking the Fischler-Susskind effect. The argument provides further justification for SL(2,{ital Z}) duality between {ital D}-strings and {ital F} (fundamental)-strings. In an Appendix we comment on recent attempts to relate the type IIA membrane to the 11-dimensional membrane. {copyright} {ital 1996 The American Physical Society.}

The dilation vertex in the path integral formulation of strings

Abstract It is shown that the explicit dilaton vertex of Fradkin and Tseytlyn must be necessarily present in order to define conformally invariant dilaton S -matrix elements in the path integral formulation of strings.

Classical and Quantum SUSY Breaking Effects in IIB Local Models

We discuss the calculation of soft supersymmery breaking terms in type IIB string theoretic models in the Large Volume Scenario (LVS). The suppression of FCNC gives a lower bound on the size of the compactification volume. This leads to soft terms which are strongly suppressed relative to the gravitino mass so that the dominant contribution to the gaugino massses comes from the Weyl anomaly. The other soft terms are essentially generated by the renormalization group running from the string scale to the TeV scale.