2,514 research outputs found
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
Vanishing of the conformal anomaly for strings in a gravitational wave
Using the non-symmetric-connection approach proposed by Osborn, we
demonstrate that, for a bosonic string in a specially chosen plane-fronted
gravitational wave and an axion background, the conformal anomaly vanishes at
the two-loop level. Under some conditions, the anomaly vanishes at all orders.Comment: Previously not available in hep-th. Published as Physics Letters B
313, 10 (1993). Plain TeX 6 pages. No figure
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
Sensitivity of deexcitation energies of superdeformed secondary minima to the density dependence of symmetry energy with the relativistic mean-field theory
The relationship between deexcitation energies of superdeformed secondary
minima relative to ground states and the density dependence of the symmetry
energy is investigated for heavy nuclei using the relativistic mean field (RMF)
model. It is shown that the deexcitation energies of superdeformed secondary
minima are sensitive to differences in the symmetry energy that are mimicked by
the isoscalar-isovector coupling included in the model. With deliberate
investigations on a few Hg isotopes that have data of deexcitation energies, we
find that the description for the deexcitation energies can be improved due to
the softening of the symmetry energy. Further, we have investigated
deexcitation energies of odd-odd heavy nuclei that are nearly independent of
pairing correlations, and have discussed the possible extraction of the
constraint on the density dependence of the symmetry energy with the
measurement of deexcitation energies of these nuclei.Comment: 14 pages, 3 figure
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 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 . 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
- …