D-Brane Recoil and Supersymmetry Breaking as a Relaxation Process

We propose a new mechanism for the formation of conical singularities on D-branes by means of recoil resulting from scattering of closed string states propagating in the (large) transverse dimensions. By viewing the (spatial part of the) four-dimensional world as a 3-brane with large transverse dimensions the above mechanism can lead to supersymmetry obstruction at the TeV scale. The vacuum remains supersymmetric while the mass spectrum picks up a supersymmetry obstructing mass splitting. The state with ``broken'' supersymmetry is not an equilibrium ground state, but is rather an excited state of the D-brane which relaxes to the supersymmetric ground state asymptotically in (cosmic) time.Comment: 9 pages revtex, uses axodraw style (Arguments clarified, citations added; no change in conclusions.

D-Brane Recoil and Supersymmetry Obstruction

We discuss a model in which our universe is pictured as a recoiling Dirichlet brane: we find that a proper treatment of the recoil leads naturally to supersymmetry obstruction on the four-dimensional world. An essential feature of our approach is the fact that the underlying worldsheet sigma model is non-critical, and the Liouville mode plays the role of the target time. Also, the extra bulk dimensions are viewed as sigma model couplings, and as such have to be averaged by appropriate summation over worldsheet genera. The recoiling brane is in an excited state rather than its ground state, to which it relaxes asymptotically in time, restoring supersymmetry. We also find that the excitation energy, which is considered as the observable effective cosmological `constant' on the brane, is naturally small and can accommodate upper bounds from observations.Comment: 9 pages, no figure

Light-Cone Broadening and TeV Scale Extra Dimensions

We examine the effect of light-cone broadening induced by quantum-gravity foam in the context of theories with ``large'' extra dimensions stretching between two parallel brane worlds. We consider the propagation of photon probes on one of the branes, including the response to graviton fluctuations, from both field- and string-theoretical viewpoints. In the latter approach, the dominant source of light-cone broadening may be the recoil of the D-brane, which scales linearly with the string coupling. Astrophysical constraints then place strong restrictions on consistent string models of macroscopic extra dimensions. The broadening we find in the field-theoretical picture seems to be close to the current sensitivity of gravity-wave interferometers, and therefore could perhaps be tested experimentally in the foreseeable future.Comment: 12 pages REVTeX, 2 axodraw figures incorporate

World-Sheet Duality, Space-Time Foam, and the Quantum Fate of a Stringy Black Hole

We interpret Minkowski black holes as world-sheet {\it spikes } which are related by world-sheet { \it duality} to {\it vortices } that correspond to Euclidean black holes. These world-sheet defects induce defects in the gauge fields of the corresponding coset Wess-Zumino descriptions of spherically-symmetric black holes. The low-temperature target space-time foam is a Minkowski black hole (spike) plasma with confined Euclidean black holes (vortices). The high-temperature phase is a {\it dense} vortex plasma described by a topological gauge field theory on the world-sheet, which possesses enhanced symmetry as in the target space-time singularity at the core of a black hole. Quantum decay via higher-genus effects induces a back-reaction which causes a Minkowski black hole to lose mass until it is indistinguishable from intrinsic fluctuations in the space-time foam.Comment: 16 pages, CERN-TH.6534/92, (correction of a minor typographical error on page 12

Electronic polarization in pentacene crystals and thin films

Electronic polarization is evaluated in pentacene crystals and in thin films on a metallic substrate using a self-consistent method for computing charge redistribution in non-overlapping molecules. The optical dielectric constant and its principal axes are reported for a neutral crystal. The polarization energies P+ and P- of a cation and anion at infinite separation are found for both molecules in the crystal's unit cell in the bulk, at the surface, and at the organic-metal interface of a film of N molecular layers. We find that a single pentacene layer with herring-bone packing provides a screening environment approaching the bulk. The polarization contribution to the transport gap P=(P+)+(P-), which is 2.01 eV in the bulk, decreases and increases by only ~ 10% at surfaces and interfaces, respectively. We also compute the polarization energy of charge-transfer (CT) states with fixed separation between anion and cation, and compare to electroabsorption data and to submolecular calculations. Electronic polarization of ~ 1 eV per charge has a major role for transport in organic molecular systems with limited overlap.Comment: 10 revtex pages, 6 PS figures embedde

The Origin of Space-Time as WW Symmetry Breaking in String Theory

Physics in the neighbourhood of a space-time metric singularity is described by a world-sheet topological gauge field theory which can be represented as a twisted $N=2$ superconformal Wess-Zumino model with a $W_{1+\infty} \otimes W_{1+\infty}$ bosonic symmetry. The measurable $W$-hair associated with the singularity is associated with Wilson loop integrals around gauge defects. The breaking of $W_{1+\infty}$ $\otimes$ $W_{1+\infty}$ $\rightarrow$ $W_{1+\infty}$ is associated with expectation values for open Wilson lines that make the metric non-singular away from the singularity. This symmetry breaking is accompanied by massless discrete `tachyon' states that appear as leg poles in $S$-matrix elements. The triviality of the $S$-matrix in the high-energy limit of the $c=1$ string model, after renormalisation by the leg pole factors, is due to the restoration of double $W$-symmetry at the singularity.Comment: 13 page

The Structure of Nanoscale Polaron Correlations in La1.2Sr1.8Mn2O7

A system of strongly-interacting electron-lattice polarons can exhibit charge and orbital order at sufficiently high polaron concentrations. In this study, the structure of short-range polaron correlations in the layered colossal magnetoresistive perovskite manganite, La1.2Sr1.8Mn2O7, has been determined by a crystallographic analysis of broad satellite maxima observed in diffuse X-ray and neutron scattering data. The resulting q=(0.3,0,1) modulation is a longitudinal octahedral-stretch mode, consistent with an incommensurate Jahn-Teller-coupled charge-density-wave fluctuations, that implies an unusual orbital-stripe pattern parallel to the directions.Comment: Reformatted with RevTe

Non-linear Dynamics in QED_3 and Non-trivial Infrared Structure

In this work we consider a coupled system of Schwinger-Dyson equations for self-energy and vertex functions in QED_3. Using the concept of a semi-amputated vertex function, we manage to decouple the vertex equation and transform it in the infrared into a non-linear differential equation of Emden-Fowler type. Its solution suggests the following picture: in the absence of infrared cut-offs there is only a trivial infrared fixed-point structure in the theory. However, the presence of masses, for either fermions or photons, changes the situation drastically, leading to a mass-dependent non-trivial infrared fixed point. In this picture a dynamical mass for the fermions is found to be generated consistently. The non-linearity of the equations gives rise to highly non-trivial constraints among the mass and effective (`running') gauge coupling, which impose lower and upper bounds on the latter for dynamical mass generation to occur. Possible implications of this to the theory of high-temperature superconductivity are briefly discussed.Comment: 29 pages LATEX, 7 eps figures incorporated, uses axodraw style. Discussion on the massless case (section 2) modified; no effect on conclusions, typos correcte

Heavy quarkonium: progress, puzzles, and opportunities

A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newly-found quarkonium-like states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K. Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D. Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A. Petrov, P. Robbe, A. Vair