7,872 research outputs found
Mode coupling theory in the FDR-preserving field theory of interacting Brownian particles
We develop a renormalized perturbation theory for the dynamics of interacting
Brownian particles, which preserves the fluctuation-dissipation relation order
by order. We then show that the resulting one-loop theory gives a closed
equation for the density correlation function, which is identical with that in
the standard mode coupling theory.Comment: version to be published in Fast Track Communication in Journal of
Physics A:Math. Theo
Cross-correlating the Thermal Sunyaev-Zel'dovich Effect and the Distribution of Galaxy Clusters
We present the analytical formulas, derived based on the halo model, to
compute the cross-correlation between the thermal Sunyaev-Zel'dovich (SZ)
effect and the distribution of galaxy clusters. By binning the clusters
according to their redshifts and masses, this cross-correlation, the so-called
stacked SZ signal, reveals the average SZ profile around the clusters. The
stacked SZ signal is obtainable from a joint analysis of an
arcminute-resolution cosmic microwave background (CMB) experiment and an
overlapping optical survey, which allows for detection of the SZ signals for
clusters whose masses are below the individual cluster detection threshold. We
derive the error covariance matrix for measuring the stacked SZ signal, and
then forecast for its detection from ongoing and forthcoming combined
CMB-optical surveys. We find that, over a wide range of mass and redshift, the
stacked SZ signal can be detected with a significant signal to noise ratio
(total S/N \gsim 10), whose value peaks for the clusters with intermediate
masses and redshifts. Our calculation also shows that the stacking method
allows for probing the clusters' SZ profiles over a wide range of scales, even
out to projected radii as large as the virial radius, thereby providing a
promising way to study gas physics at the outskirts of galaxy clusters.Comment: 11 pages, 6 figures, 3 tables, minor revisions reflect PRD published
versio
Magnetic Diode Effect in Double Barrier Tunnel Junctions
A quantum statistical theory of spin-dependent tunneling through asymmetric
magnetic double barrier junctions is presented which describes ballistic
and diffuse tunneling by a single analytical expression. It is evidenced that
the key parameter for the transition between these two tunneling regimes is the
electron scattering. For these junctions a strong asymmetric behaviour in the
I-V characteristics and the tunnel magnetoresistance (TMR) is predicted which
can be controlled by an applied magnetic field. This phenomenon relates to the
quantum well states in the middle metallic layer. The corresponding resonances
in the current and the TMR are drastically phase shifted under positive and
negative voltage.Comment: 10 pages, 4 Postscript figures, submitted to Europhys. Let
Optimizing future imaging survey of galaxies to confront dark energy and modified gravity models
We consider the extent to which future imaging surveys of galaxies can
distinguish between dark energy and modified gravity models for the origin of
the cosmic acceleration. Dynamical dark energy models may have similar
expansion rates as models of modified gravity, yet predict different growth of
structure histories. We parameterize the cosmic expansion by the two
parameters, and , and the linear growth rate of density fluctuations
by Linder's , independently. Dark energy models generically predict
, while the DGP model . To determine
if future imaging surveys can constrain within 20 percent (or
), we perform the Fisher matrix analysis for a weak lensing
survey such as the on-going Hyper Suprime-Cam (HSC) project. Under the
condition that the total observation time is fixed, we compute the Figure of
Merit (FoM) as a function of the exposure time \texp. We find that the
tomography technique effectively improves the FoM, which has a broad peak
around \texp\simeq {\rm several}\sim 10 minutes; a shallow and wide survey is
preferred to constrain the parameter. While
cannot be achieved by the HSC weak-lensing survey alone, one can improve the
constraints by combining with a follow-up spectroscopic survey like WFMOS
and/or future CMB observations.Comment: 18 pages, typos correcte
Combining cluster observables and stacked weak lensing to probe dark energy: Self-calibration of systematic uncertainties
We develop a new method of combining cluster observables (number counts and
cluster-cluster correlation functions) and stacked weak lensing signals of
background galaxy shapes, both of which are available in a wide-field optical
imaging survey. Assuming that the clusters have secure redshift estimates, we
show that the joint experiment enables a self-calibration of important
systematic errors including the source redshift uncertainty and the cluster
mass-observable relation, by adopting a single population of background source
galaxies for the lensing analysis. It allows us to use the relative strengths
of stacked lensing signals at different cluster redshifts for calibrating the
source redshift uncertainty, which in turn leads to accurate measurements of
the mean cluster mass in each bin. In addition, our formulation of stacked
lensing signals in Fourier space simplifies the Fisher matrix calculations, as
well as the marginalization over the cluster off-centering effect, the most
significant uncertainty in stacked lensing. We show that upcoming wide-field
surveys yield stringent constraints on cosmological parameters including dark
energy parameters, without any priors on nuisance parameters that model
systematic uncertainties. Specifically, the stacked lensing information
improves the dark energy FoM by a factor of 4, compared to that from the
cluster observables alone. The primordial non-Gaussianity parameter can also be
constrained with a level of f_NL~10. In this method, the mean source redshift
is well calibrated to an accuracy of 0.1 in redshift, and the mean cluster mass
in each bin to 5-10% accuracies, which demonstrates the success of the
self-calibration of systematic uncertainties from the joint experiment.
(Abridged)Comment: 29 pages, 17 figures, 6 tables, accepted for publication in Phys.
Rev.
Critical fluctuations and breakdown of Stokes-Einstein relation in the Mode-Coupling Theory of glasses
We argue that the critical dynamical fluctuations predicted by the
mode-coupling theory (MCT) of glasses provide a natural mechanism to explain
the breakdown of the Stokes-Einstein relation. This breakdown, observed
numerically and experimentally in a region where MCT should hold, is one of the
major difficulty of the theory, for which we propose a natural resolution based
on the recent interpretation of the MCT transition as a bona fide critical
point with a diverging length scale. We also show that the upper critical
dimension of MCT is d_c=8.Comment: Proceedings of the workshop on non-equilibrium phenomena in
supercooled fluids, glasses and amorphous materials (17-22 September, 2006,
Pisa
A Molecular Hydrodynamic Theory of Supercooled Liquids and Colloidal Suspensions under Shear
We extend the conventional mode-coupling theory of supercooled liquids to
systems under stationary shear flow. Starting from generalized fluctuating
hydrodynamics, a nonlinear equation for the intermediate scattering function is
constructed. We evaluate the solution numerically for a model of a two
dimensional colloidal suspension and find that the structural relaxation time
decreases as with an exponent , where
is the shear rate. The results are in qualitative agreement with
recent molecular dynamics simulations. We discuss the physical implications of
the results.Comment: 5 pages, 1 figur
Bi-layer Heisenberg model studied by the Schwinger-boson Gutzwiller-projection method
A two-dimensional bi-layer, square lattice Heisenberg model with different
intraplane() and interplane() couplings is
investigated. The model is first solved in the Schwinger boson mean-field
approximation. %It is shown that order-disorder transition occurs as the
interplane Coupling %is increased. The critical ratio is J_{\perp/\p=4.48J
Then the solution is Gutzwiller projected to satisfy the local constraint that
there should be only one boson at each site. For these wave functions, we
perform variational Monte Carlo simulation up to sites.
It is shown that the N\'eel order is destroyed as the interplane coupling is
increased. The obtained critical value, , is
smaller than that by the mean-field theory. Excitation spectrum is calculated
by a single mode approximation. It is shown that energy gap develops once the
N\'eel order is destroyed.Comment: 19 pages(including figure captions) RevTex3.0, 10 figures, available
upon reques
Superconductivity of Quasi-Two-Dimensional Tight-Binding Electrons in a Strong Magnetic Field
We have investigated the transition temperature of
superconductiv ity in quasi-two-dimensional (Q2D) tight-binding electrons in a
strong magnetic field. When the magnetic field is parallel to 2D conducting
plane, of the Q2D superconductor is shown to increase in an
oscillatory manner as the magnetic field becomes large and to reach in a strong magnetic f ield limit for the spin-triplet superconductor.
We consider the cases of on-site and nearest sites attractive interaction, and
calculate the magnetic field depe ndences of the transition temperature for
various types of symmetry. The first o rder transition from -wave to
-wave is shown to occur at T w hen the magnetic field is
parallel to the direction, which will be observed in a triplet
superconductor, SrRuO.Comment: 13pages,6figure
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