Stability of AdSp×Mq compactifications without supersymmetry

We study the stability of Freund-Rubin compactifications, AdSp×Mq, of (p+q)-dimensional gravity theories with a q-form field strength and no cosmological term. We show that the general AdSp×S^q vacuum is classically stable against small fluctuations, in the sense that all modes satisfy the Breitenlohner-Freedman bound. In particular, the compactifications used in the recent discussion of the proposed bosonic M theory are perturbatively stable. Our analysis treats all modes arising from the graviton and the q form, and is completely independent of supersymmetry. From the masses of the linearized perturbations, we obtain the dimensions of some operators in possible holographic dual CFT’s. Solutions with more general compact Einstein spaces need not be stable, and in particular AdSp×S^n×S^(q-n) is unstable for q~9. We also study the AdS4×S^6 compactification of massive type IIA supergravity, which differs from the usual Freund-Rubin compactification in that there is a cosmological term already in ten dimensions. This nonsupersymmetric vacuum is unstable

pQCD vs. AdS/CFT Tested by Heavy Quark Energy Loss

We predict the charm and bottom quark nuclear modification factors using weakly coupled pQCD and strongly coupled AdS/CFT drag methods. The log(pT/M_Q)/pT dependence of pQCD loss and the momentum independence of drag loss lead to different momentum dependencies for the R_{AA} predictions. This difference is enhanced by examining a new experimental observable, the double ratio of charm to bottom nuclear modification factors, R^{cb}=R^c_{AA}/R^b_{AA}. At LHC the weakly coupled theory predicts R^{cb} goes to 1; whereas the strongly coupled theory predicts R^{cb} .2 independent of pT. At RHIC the differences are less dramatic, as the production spectra are harder, but the drag formula is applicable to higher momenta, due to the lower temperature.Comment: 6 pages, 4 figures. Proceedings for the International Conference on Strangeness in Quark Matter (SQM 2007), Levoca, Slovakia, 24-29 June 200

Efficiency of a Brownian information machine

A Brownian information machine extracts work from a heat bath through a feedback process that exploits the information acquired in a measurement. For the paradigmatic case of a particle trapped in a harmonic potential, we determine how power and efficiency for two variants of such a machine operating cyclically depend on the cycle time and the precision of the positional measurements. Controlling only the center of the trap leads to a machine that has zero efficiency at maximum power whereas additional optimal control of the stiffness of the trap leads to an efficiency bounded between 1/2, which holds for maximum power, and 1 reached even for finite cycle time in the limit of perfect measurements.Comment: 9 pages, 2 figure

Entanglement and entropy operator for strings in pp-wave time dependent background

In this letter new aspects of string theory propagating in a pp-wave time dependent background with a null singularity are explored. It is shown the appearance of a 2d entanglement entropy dynamically generated by the background. For asymptotically flat observers, the vacuum close to the singularity is unitarily inequivalent to the vacuum at $\tau = -\infty$ and it is shown that the 2d entanglement entropy diverges close to this point. As a consequence, the positive time region is inaccessible for observers in $\tau =-\infty$. For a stationary measure, the vacuum at finite time is seen by those observers as a thermal state and the information loss is encoded as a heat bath of string states.Comment: revtex4, 15 pages, revised version to appear in Physics Letters

Neutrino Trapping in a Supernova and Ion Screening

Neutrino-nucleus elastic scattering is reduced in dense matter because of correlations between ions. The static structure factor for a plasma of electrons and ions is calculated from Monte Carlo simulations and parameterized with a least squares fit. Our results imply a large increase in the neutrino mean free path. This strongly limits the trapping of neutrinos in a supernova by coherent neutral current interactions.Comment: 9 pages, 1 postscript figure using epsf.st

Stringy Probe Particle and Force Balance

We directly derive the classical equation of motion, which governs the centre of mass of a test string, from the string action. In a certain case, the equation is basically same as one derived by Papapetrou, Dixon and Wald for a test extended body. We also discuss the force balance using a stringy probe particle for an exact spinning multi-soliton solution of Einstein-Maxwell-Dilaton-Axion theory. It is well known that the force balance condition yields the saturation of the Bogomol'nyi type bound in the lowest order. In the present formulation the gyromagnetic ratio of the stringy probe particle is automatically determined to be $g=2$ which is the same value as the background soliton. As a result we can confirm the force balance via the gravitational spin-spin interaction.Comment: 8 pages, references added, comments added, Phys. Rev. D accepte