http://inspirehep.net/record/499969/files/arXiv:hep-th_9905111.pdf

Large N Field Theories, String Theory and Gravity

Superstring theoryをめぐって(放談室)

Journal of Physics Condensed Matter: Preface

In the first part of this paper we find supergravity solutions corresponding to branes on worldvolumes of the form Rd×Σ where Σ is a Riemann surface. These theories arise when we wrap branes on holomorphic Riemann surfaces inside K3 or CY manifolds. In some cases the theory at low energies is a conformal field theory with two less dimensions. We find some non-singular supersymmetric compactifications of M-theory down to AdS5. We also propose a criterion for permissible singularities in supergravity solutions. In the second part of this paper, which can be read independently of the first, we show that there are no non-singular Randall-Sundrum or de-Sitter compactifications for large class of gravity theories.

http://cds.cern.ch/record/445802/files/0007018.pdf

Supergravity description of field theories on curved manifolds and a no go theorem

Flux compactifications in string theory: A Comprehensive review

A proposal on some microscopic aspects of the AdS/CFT duality

Misner space, also known as the Lorentzian orbifold $R^{1,1}/boost$, is one of the simplest examples of a cosmological singularity in string theory. In this work, the study of weakly coupled closed strings on this space is pursued in several directions: (i) physical states in the twisted sectors are found to come in two kinds: short strings, which wind along the compact space-like direction in the cosmological (Milne) regions, and long strings, which wind along the compact time-like direction in the (Rindler) whiskers. The latter can be viewed as infinitely long static open strings, stretching from Rindler infinity to a finite radius and folding back onto themselves. (ii) As in the Schwinger effect, tunneling between these states corresponds to local pair production of winding strings. The tunneling rate approaches unity as the winding number $w$ gets large, as a consequence of the singular geometry. (iii) The one-loop string amplitude has singularities on the moduli space, associated to periodic closed string trajectories in Euclidean time. In the untwisted sector, they can be traced to the combined existence of CTCs and Regge trajectories in the spectrum. In the twisted sectors, they indicate pair production of winding strings. (iv) At a classical level and in sufficiently low dimension, the condensation of winding strings can indeed lead to a bounce, although the required initial conditions are not compatible with Misner geometry at early times. (v) The semi-classical analysis of winding string pair creation can be generalized to more general (off-shell) geometries. We show that a regular geometry regularizes the divergence at large winding number.

Closed Strings in Misner Space: Cosmological Production of Winding Strings

We examine the scattering behavior from a single non magnetic impurity in a helical liquid. A helical liquid is a one dimensional system with a pair of counter propagating edge states, which are time reversal partners. In the absence of a magnetic field, time reversal symmetry is conserved and hence single particle scattering is prohibited. However, multi particle processes are possible. We examine the backscattering current and noise, and derive the effective scattering charge. A magnetic field enhances the backscattered current, but reduces the effective scattering charge. We find that the scattering charge can vary between $e$ and $2e$, depending on the strength of electron-electron interactions and the magnetic field.

Single and multi-particle scattering in Helical liquid with an impurity

Stationary solutions of 5D supergravity with U(1) isometry can be efficiently studied by dimensional reduction to three dimensions, where they reduce to solutions to a locally supersymmetric non-linear sigma model. We generalize this procedure to 5D gauged supergravity, and identify the corresponding gauging in 3D. We pay particular attention to the case where the Killing spinor is non constant along the fibration, which results, even for ungauged supergravity in 5D, in an additional gauging in 3D, without introducing any extra potential. We further study SU(2)\times U(1) symmetric solutions, which correspond to geodesic motion on the sigma model (with potential in the gauged case). We identify and study the algebra of BPS constraints relevant for the Breckenridge-Myers-Peet-Vafa black hole, the Gutowski-Reall black hole and several other BPS solutions, and obtain the corresponding radial wave functions in the semi-classical approximation.

5D Black Holes and Non-linear Sigma Models

In a class of anomaly mediated supersymmetry breaking (AMSB) models, the splitting in the $W$-ino multiplet turns out to be very small, such as the often-quoted 170 MeV in minimal AMSB, which originates from minimal supersymmetric standard model loops. Such a small mass gap is potentially a window into higher scale physics, as it may be sensitive to higher-dimensional operators. We show that still within AMSB one can get a much larger splitting in the $W$-ino multiplet---a few GeV---if the scale of the new physics is comparable to the gravitino mass (which is indeed often the scale of new physics in anomaly mediation).

Micha Berkooz

Papers

A proposal on some microscopic aspects of the AdS/CFT duality

Closed Strings in Misner Space: Cosmological Production of Winding Strings

Single and multi-particle scattering in Helical liquid with an impurity

5D Black Holes and Non-linear Sigma Models

Splitting the W -ino multiplet by higher-dimensional operators in anomaly mediation