Is string theory a theory of quantum gravity?

Some problems in finding a complete quantum theory incorporating gravity are discussed. One is that of giving a consistent unitary description of high-energy scattering. Another is that of giving a consistent quantum description of cosmology, with appropriate observables. While string theory addresses some problems of quantum gravity, its ability to resolve these remains unclear. Answers may require new mechanisms and constructs, whether within string theory, or in another framework.Comment: Invited contribution for "Forty Years of String Theory: Reflecting on the Foundations," a special issue of Found. Phys., ed. by G 't Hooft, E. Verlinde, D. Dieks, S. de Haro. 32 pages, 5 figs., harvmac. v2: final version to appear in journal (small revisions

Black hole information, unitarity, and nonlocality

The black hole information paradox apparently indicates the need for a fundamentally new ingredient in physics. The leading contender is nonlocality. Possible mechanisms for the nonlocality needed to restore unitarity to black hole evolution are investigated. Suggestions that such dynamics arises from ultra-planckian modes in Hawking's derivation are investigated and found not to be relevant, in a picture using smooth slices spanning the exterior and interior of the horizon. However, no simultaneous description of modes that have fallen into the black hole and outgoing Hawking modes can be given without appearance of a large kinematic invariant, or other dependence on ultra-planckian physics; a reliable argument for information loss thus has not been constructed. This suggests that strong gravitational dynamics is important. Such dynamics has been argued to be fundamentally nonlocal in extreme situations, such as those required to investigate the fate of information.Comment: 34 pages, 4 figures. Major revision of hep-th/0604047. v2: minor corrections and added referenc

A hard coat, a tough choice? The effects of host seed morphology and mechanics on the egg laying behaviour of the bruchid beetle, Callosobruchus maculatus.

This study investigated whether the egg laying behaviour of Callosobruchus maculatus, an important storage pest of leguminous seed crops, was related to the mechanical properties of the host seed. The hypothesis was that females avoid laying eggs on seeds with particularly tough seed coats and hard cotyledons to reduce the resistance their larvae are subjected to when they bore into the seed to complete their development. Females were presented with seeds from three leguminous species: Vigna unguiculata, V. angularis and V. radiata. The distribution of oviposition sites on the seed's surface was related to the morphology and mechanical properties of the seed. Vickers microhardness and fracture tests were used to investigate regional variation and compare the properties of seeds with and without eggs adhered to their surface. There were no significant regional differences in the hardness of the cotyledon material along the longitudinal axis of the seed (P > 0.05). However, there were significant differences between the mechanical properties of the seed coat and the cotyledons; in V. unguiculata the seed coat was tougher, 1249 ± 80.8 J m−2, than the cotyledons, 402 ± 30.0 J m−2 (P 0.05). Mechanical data are discussed in relation to the egg laying behaviour of C. maculatus

Locality in quantum gravity and string theory

Breakdown of local physics in string theory at distances longer than the string scale is investigated. Such nonlocality would be expected to be visible in ultrahigh-energy scattering. The results of various approaches to such scattering are collected and examined. No evidence is found for non-locality from strings whose length grows linearly with the energy. However, local quantum field theory does apparently fail at scales determined by gravitational physics, particularly strong gravitational dynamics. This amplifies locality bound arguments that such failure of locality is a fundamental aspect of physics. This kind of nonlocality could be a central element of a possible loophole in the argument for information loss in black holes.Comment: 26 pages, 3 figures, harvmac. v2: minor changes to bring into accord with revised paper hep-th/060519

Cosmological diagrammatic rules

A simple set of diagrammatic rules is formulated for perturbative evaluation of ``in-in" correlators, as is needed in cosmology and other nonequilibrium problems. These rules are both intuitive, and efficient for calculational purposes.Comment: 7 pages, 3 figure

Nonlocality vs. complementarity: a conservative approach to the information problem

A proposal for resolution of the information paradox is that "nice slice" states, which have been viewed as providing a sharp argument for information loss, do not in fact do so as they do not give a fully accurate description of the quantum state of a black hole. This however leaves an information *problem*, which is to provide a consistent description of how information escapes when a black hole evaporates. While a rather extreme form of nonlocality has been advocated in the form of complementarity, this paper argues that is not necessary, and more modest nonlocality could solve the information problem. One possible distinguishing characteristic of scenarios is the information retention time. The question of whether such nonlocality implies acausality, and particularly inconsistency, is briefly addressed. The need for such nonlocality, and its apparent tension with our empirical observations of local quantum field theory, may be a critical missing piece in understanding the principles of quantum gravity.Comment: 11 pages of text and figures, + references. v2 minor text. v3 small revisions to match final journal versio

Gauge/String-Gravity Duality and Froissart Bound

The gauge/string-gravity duality correspondence opened renewed hope and possibility to address some of the fundamental and non-perturbative QCD problems in particle physics, such as hadron spectrum and Regge behavior of the scattering amplitude at high energies. One of the most fundamental and long-standing problem is the high energy behavior of total cross-sections. According to a series of exhaustive tests by the COMPETE group, (1). total cross-sections have a universal Heisenberg behavior in energy corresponding to the maximal energy behavior allowed by the Froissart bound, i.e., $A + B ln^2 (s/s_0)$ with $B \sim 0.32 mb$ and $s_0 \sim 34.41 GeV^2$ for all reactions, and (2). the factorization relation among $\sigma_{pp, even}, \sigma_{\gamma p}, and \sigma_{\gamma \gamma}$ is well satisfied by experiments. I discuss the recent interesting application of the gauge/string-gravity duality of $AdS/CFT$ correspondence with a deformed background metric so as to break the conformal symmetry that can lead to the Heisenberg behavior of rising total cross-sections, and present some preliminary results on the high energy QCD from Planckian scattering in $AdS$ and black-hole production.Comment: 10 pages, Presented to the Coral Gables Conference 2003, Launching of BelleE\'poque in High Energy Physics and Cosmology, 17 - 21 December 2003, Fort Lauderdale, Florid

Dynamics of warped compactifications and the shape of the warped landscape

The dynamics of warped/flux compactifications is studied, including warping effects, providing a firmer footing for investigation of the "landscape." We present a general formula for the four-dimensional potential of warped compactifications in terms of ten-dimensional quantities. This allows a systematic investigation of moduli-fixing effects and potentials for mobile branes. We provide a necessary criterion, "slope-dominance," for evading "no-go" results for de Sitter vacua. We outline the ten-dimensional derivation of the non-perturbative effects that should accomplish this in KKLT examples, and outline a systematic discussion of their corrections. We show that potentials for mobile branes receive generic contributions inhibiting slow-roll inflation. We give a linearized analysis of general scalar perturbations of warped IIB compactifications, revealing new features for both time independent and dependent moduli, and new aspects of the kinetic part of the four-dimensional effective action. The universal Kahler modulus is found_not_ to be a simple scaling of the internal metric, and a prescription is given for defining holomorphic Kahler moduli, including warping effects. In the presence of mobile branes, this prescription elucidates couplings between bulk and brane fields. Our results are thus relevant to investigations of the existence of de Sitter vacua in string theory, and of their phenomenology, cosmology, and statistics.Comment: (80 pages; two appendices; harvmac. v3: minor corrections, and references added. v4: argument that pure Kahler deformations are flat.

Entropy in Black Hole Pair Production

Pair production of Reissner-Nordstrom black holes in a magnetic field can be described by a euclidean instanton. It is shown that the instanton amplitude contains an explicit factor of $e^{A/4}$, where $A$ is the area of the event horizon. This is consistent with the hypothesis that $e^{A/4}$ measures the number of black hole states.Comment: 24 pages (harvmac l mode