What is Holography in the Plane-Wave Limit of AdS/CFT Correspondence ?

The issue of holographic principle in the PP-wave limit of the AdS/CFT correspondence is discussed, in the hope of clarifying some confusions in the literature. We show that, in the plane-wave limit, the relation between the partition function in the bulk and the gauge-invariant correlation functions on the boundary should be interpreted on the basis of a tunneling picture in the semi-classical approximation which is appropriate for the plane-wave limit. This leads to a natural relation between Euclidean S-matrix in the bulk and the short-distance operator-product expansion of the so-called BMN operators on the boundary.Comment: 17 pages, 2 figures, an expanded written version of talk at the Nishinomiya Yukawa Memorial Symposium, Nishinomiya, November, 200

A digital library of language learning exercises

Recent years have seen widespread adoption of the Internet for language teaching and learning. Interactive systems on the World-Wide Web provide useful alternatives to face-to-face tuition, and both teachers and learners can benefit from the exercises available. However, although there is a wealth of suitable material, it is hard to find because it is scattered around the web. Moreover, teachers are restricted by the material that is available, and cannot provide their own. To tackle these problems we have constructed a digital library of language learning exercises that presents students with different kinds of exercise, and also lets teachers contribute new material. We first reviewed existing language learning systems on the web in order to develop a taxonomy of exercise types used for language activity. A prototype, ELLE, based on this taxonomy, provides various kinds of interactive exercises using material that teachers submit. The system has been evaluated by practicing language teachers

Cargese Lectures on the Kerr/CFT Correspondence

We give a short introduction, beginning with the Kerr geometry itself, to the basic results, motivation, open problems and future directions of the Kerr/CFT correspondence.Comment: Lectures given by A. Strominger at Cargese 2010. References update

Historical and futuristic perturbative and non-perturbative aspects of QCD jet physics

A brief review of jet physics is presented with an emphasis upon open theoretical problems (non-perturbative domain; hadronization and confinement) and new phenomena (hadroproduction in heavy ion collisions).Comment: Invited talk at the XXXIV International Symposium on Multiparticle Dynamics, Sonoma State University, California, USA, July 26 - August 1, 200

Holographic Protection of Chronology in Universes of the Godel Type

We analyze the structure of supersymmetric Godel-like cosmological solutions of string theory. Just as the original four-dimensional Godel universe, these solutions represent rotating, topologically trivial cosmologies with a homogeneous metric and closed timelike curves. First we focus on "phenomenological" aspects of holography, and identify the preferred holographic screens associated with inertial comoving observers in Godel universes. We find that holography can serve as a chronology protection agency: The closed timelike curves are either hidden behind the holographic screen, or broken by it into causal pieces. In fact, holography in Godel universes has many features in common with de Sitter space, suggesting that Godel universes could represent a supersymmetric laboratory for addressing the conceptual puzzles of de Sitter holography. Then we initiate the investigation of "microscopic" aspects of holography of Godel universes in string theory. We show that Godel universes are T-dual to pp-waves, and use this fact to generate new Godel-like solutions of string and M-theory by T-dualizing known supersymmetric pp-wave solutions.Comment: 35 pages, 5 figures. v2: typos corrected, references adde

Failure of Perturbation Theory Near Horizons: the Rindler Example

Persistent puzzles to do with information loss for black holes have stimulated critical reassessment of the domain of validity of semiclassical EFT reasoning in curved spacetimes, particularly in the presence of horizons. We argue here that perturbative predictions about evolution for very long times near a horizon are subject to problems of secular growth - i.e. powers of small couplings come systematically together with growing functions of time. Such growth signals a breakdown of naive perturbative calculations of late-time behaviour, regardless of how small ambient curvatures might be. Similar issues of secular growth also arise in cosmology, and we build evidence for the case that such effects should be generic for gravitational fields. In particular, inferences using free fields coupled only to background metrics can be misleading at very late times due to the implicit assumption they make of perturbation theory when neglecting other interactions. Using the Rindler horizon as an example we show how this secular growth parallels similar phenomena for thermal systems, and how it can be resummed to allow late-time inferences to be drawn more robustly. Some comments are made about the appearance of an IR/UV interplay in this calculation, as well as on the possible relevance of our calculations to predictions near black-hole horizons.Comment: LaTeX, 17 pages plus appendix; added references and subsection on back-reactio