59,649 research outputs found
Non-equilibrium behavior at a liquid-gas critical point
Second-order phase transitions in a non-equilibrium liquid-gas model with
reversible mode couplings, i.e., model H for binary-fluid critical dynamics,
are studied using dynamic field theory and the renormalization group. The
system is driven out of equilibrium either by considering different values for
the noise strengths in the Langevin equations describing the evolution of the
dynamic variables (effectively placing these at different temperatures), or
more generally by allowing for anisotropic noise strengths, i.e., by
constraining the dynamics to be at different temperatures in d_par- and
d_perp-dimensional subspaces, respectively. In the first, case, we find one
infrared-stable and one unstable renormalization group fixed point. At the
stable fixed point, detailed balance is dynamically restored, with the two
noise strengths becoming asymptotically equal. The ensuing critical behavior is
that of the standard equilibrium model H. At the novel unstable fixed point,
the temperature ratio for the dynamic variables is renormalized to infinity,
resulting in an effective decoupling between the two modes. We compute the
critical exponents at this new fixed point to one-loop order. For model H with
spatially anisotropic noise, we observe a critical softening only in the
d_perp-dimensional sector in wave vector space with lower noise temperature.
The ensuing effective two-temperature model H does not have any stable fixed
point in any physical dimension, at least to one-loop order. We obtain formal
expressions for the novel critical exponents in a double expansion about the
upper critical dimension d_c = 4 - d_par and with respect to d_par, i.e., about
the equilibrium theory.Comment: 17 pages, revtex, one figure and EPJB style files include
Boundary Conditions for Kerr-AdS Perturbations
The Teukolsky master equation and its associated spin-weighted spheroidal
harmonic decomposition simplify considerably the study of linear gravitational
perturbations of the Kerr(-AdS) black hole. However, the formulation of the
problem is not complete before we assign the physically relevant boundary
conditions. We find a set of two Robin boundary conditions (BCs) that must be
imposed on the Teukolsky master variables to get perturbations that are
asymptotically global AdS, i.e. that asymptotes to the Einstein Static
Universe. In the context of the AdS/CFT correspondence, these BCs allow a
non-zero expectation value for the CFT stress-energy tensor while keeping fixed
the boundary metric. When the rotation vanishes, we also find the gauge
invariant differential map between the Teukolsky and the Kodama-Ishisbashi
(Regge-Wheeler-Zerilli) formalisms. One of our Robin BCs maps to the scalar
sector and the other to the vector sector of the Kodama-Ishisbashi
decomposition. The Robin BCs on the Teukolsky variables will allow for a
quantitative study of instability timescales and quasinormal mode spectrum of
the Kerr-AdS black hole. As a warm-up for this programme, we use the Teukolsky
formalism to recover the quasinormal mode spectrum of global AdS-Schwarzschild,
complementing previous analysis in the literature.Comment: 33 pages, 6 figure
AdS nonlinear instability: moving beyond spherical symmetry
Anti-de Sitter (AdS) is conjectured to be nonlinear unstable to a weakly
turbulent mechanism that develops a cascade towards high frequencies, leading
to black hole formation [1,2]. We give evidence that the gravitational sector
of perturbations behaves differently from the scalar one studied in [2]. In
contrast with [2], we find that not all gravitational normal modes of AdS can
be nonlinearly extended into periodic horizonless smooth solutions of the
Einstein equation. In particular, we show that even seeds with a single normal
mode can develop secular resonances, unlike the spherically symmetric scalar
field collapse studied in [2]. Moreover, if the seed has two normal modes, more
than one resonance can be generated at third order, unlike the spherical
collapse of [2]. We also show that weak turbulent perturbative theory predicts
the existence of direct and inverse cascades, with the former dominating the
latter for equal energy two-mode seeds.Comment: 7 pages, no figures, 2 table
Klein-Gordon oscillator in a topologically nontrivial space-time
In this study, we analyze solutions of the wave equation for scalar particles
in a space-time with nontrivial topology. Solutions for the Klein--Gordon
oscillator are found considering two configurations of this space-time. In the
first one, it is assumed the space where the metric is
written in the usual inertial frame of reference. In the second case, we
consider a rotating reference frame adapted to the circle S1. We obtained
compact expressions for the energy spectrum and for the particles wave
functions in both configurations. Additionally, we show that the energy
spectrum of the solution associated to the rotating system has an additional
term that breaks the symmetry around
Ages and metallicities of star clusters: new calibrations and diagnostic diagrams from visible integrated spectra
We present homogeneous scales of ages and metallicities for star clusters
from very young objects, through intermediate-age ones up to the oldest known
clusters. All the selected clusters have integrated spectra in the visible
range, as well as reliable determinations of their ages and metallicities. From
these spectra equivalent widths (EWs) of KCaII, Gband(CH) and MgI metallic, and
Hdelta, Hgamma and Hbeta Balmer lines have been measured homogeneously. The
analysis of these EWs shows that the EW sums of the metallic and Balmer H
lines, separately, are good indicators of cluster age for objects younger than
10 Gyr, and that the former is also sensitive to cluster metallicity for ages
greater than 10 Gyr. We propose an iterative procedure for estimating cluster
ages by employing two new diagnostic diagrams and age calibrations based on the
above EW sums. For clusters older than 10 Gyr, we also provide a calibration to
derive their overall metal contents.Comment: 9 pages, 4 figures, accepted by A&
On the P-representable subset of all bipartite Gaussian separable states
P-representability is a necessary and sufficient condition for separability
of bipartite Gaussian states only for the special subset of states whose
covariance matrix are locally invariant. Although this
special class of states can be reached by a convenient
transformation over an arbitrary covariance matrix, it represents a loss of
generality, avoiding inference of many general aspects of separability of
bipartite Gaussian states.Comment: Final version with new results added. Slightly more detailed than the
accepted manuscript (to appear in Phys. Rev. A
A model for the time uncertainty measurements in the Auger surface detector array
The precise determination of the arrival direction of cosmic rays is a
fundamental prerequisite for the search for sources or the study of their
anisotropies on the sky. One of the most important aspects to achieve an
optimal measurement of these directions is to properly take into account the
measurement uncertainties in the estimation procedure. In this article we
present a model for the uncertainties associated with the time measurements in
the Auger surface detector array. We show that this model represents well the
measurement uncertainties and therefore provides the basis for an optimal
determination of the arrival direction. With this model and a description of
the shower front geometry it is possible to estimate, on an event by event
basis, the uncertainty associated with the determination of the arrival
directions of the cosmic rays
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