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

We argue that vacua of string theory which asymptote at weak coupling to linear dilaton backgrounds are holographic. The full string theory in such vacua is ``dual'' to a theory without gravity in fewer dimensions. The dual theory is generically not a local quantum field theory. Excitations of the string vacuum, which can be studied in the weak coupling region using worldsheet methods, give rise to observables in the dual theory. An interesting example is string theory in the near-horizon background of parallel NS5-branes, the CHS model, which is dual to the decoupled NS5-brane theory (``little string theory''). This duality can be used to study some of the observables in this theory and some of their correlation functions. Another interesting example is the ``old'' matrix model, which gives a holographic description of two dimensional string theory.

Linear Dilatons, NS5-branes and Holography

We identify a large family of 1/16 BPS operators in = 4 SYM that qualitatively reproduce the relations between charge, angular momentum and entropy in regular supersymmetric AdS5 black holes when the main contribution to their masses is given by their angular momentum.

A Fermi surface model for large supersymmetric AdS 5 black holes

Arguably the simplest model of a cosmological singularity in string theory, the Lorentzian orbifold 1,1/boost is known to lead to severe divergences in scattering amplitudes of untwisted states, indicating a large backreaction towards the singularity. In this work we take a first step in investigating whether condensation of twisted states may remedy this problem and resolve the spacelike singularity. By using the formal analogy with charged open strings in an electric field, we argue that, contrary to earlier claims, twisted sectors do contain physical scattering states, which can be viewed as charged particles in an electric field. Correlated pairs of twisted states will therefore be produced by the ordinary Schwinger mechanism. For open strings in an electric field, on-shell wave functions for the zero-modes are determined, and shown to analytically continue to non-normalizable modes of the usual Landau harmonic oscillator in Euclidean space. Closed string scattering states of the Milne orbifold continue to non-normalizable modes in an unusual Euclidean orbifold of 2 by a rotation by an irrational angle. Irrespective of the formal analogy with the Milne Universe, open strings in a constant electric field, or colliding D-branes, may also serve as a useful laboratory to study time-dependence in string theory.

https://iopscience.iop.org/article/10.1088/1475-7516/2003/11/007/pdf

Strings in an electric field, and the Milne Universe

Misner space, also known as the Lorentzian orbifold , 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, tunnelling between these states corresponds to local pair production of winding strings. The tunnelling 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.

http://iopscience.iop.org/article/10.1088/1475-7516/2004/08/004/pdf

Closed strings in Misner space: cosmological production of winding strings

We exhibit a simple class of exactly marginal ``double-trace'' deformations of two-dimensional conformal field theories (CFTs) which have ${\mathrm{AdS}}_{3}$ duals, in which the deformation is given by a product of left- and right-moving U(1) currents. In this special case the deformation on ${\mathrm{AdS}}_{3}$ is generated by a local boundary term in three dimensions, which changes the physics also in the bulk via bulk-boundary propagators. However, the deformation is nonlocal in six dimensions and on the string world sheet, as in generic nonlocal string theories. Because of the simplicity of the deformation we can explicitly make computations in the nonlocal string theory and compare them to CFT computations, and we obtain precise agreement. We discuss the effect of the deformation on closed strings and on D branes. The examples we analyze include a supersymmetry-breaking but exactly marginal ``double-trace'' deformation, which is dual to a string theory in which no destabilizing tadpoles are generated for moduli nonperturbatively in all couplings, despite the absence of supersymmetry. We explain how this cancellation works on the gravity side in string perturbation theory, and also nonperturbatively at leading order in the deformation parameter. We also discuss possible flat space limits of our construction.

Micha Berkooz

Papers

Linear Dilatons, NS5-branes and Holography

A Fermi surface model for large supersymmetric AdS 5 black holes

Strings in an electric field, and the Milne Universe

Closed strings in Misner space: cosmological production of winding strings

Nonlocal string theories on AdS 3 ×S 3 and stable nonsupersymmetric backgrounds