13,514 research outputs found
Relativistic Einstein-Podolsky-Rosen correlation and Bell's inequality
We formulate the Einstein-Podolsky-Rosen (EPR) gedankenexperiment within the
framework of relativistic quantum theory to analyze a situation in which
measurements are performed by moving observers. We point out that under certain
conditions the perfect anti-correlation of an EPR pair of spins in the same
direction is deteriorated in the moving observers' frame due to the Wigner
rotation, and show that the degree of the violation of Bell's inequality prima
facie decreases with increasing the velocity of the observers if the directions
of the measurement are fixed. However, this does not imply a breakdown of
non-local correlation since the perfect anti-correlation is maintained in
appropriately chosen different directions. We must take account of this
relativistic effect in utilizing in moving frames the EPR correlation and the
violation of Bell's inequality for quantum communication.Comment: 33 pages, 6 figure
On Recovering the Nonlinear Bias Function from Counts in Cells Measurements
We present a simple and accurate method to constrain galaxy bias based on the
distribution of counts in cells. The most unique feature of our technique is
that it is applicable to non-linear scales, where both dark matter statistics
and the nature of galaxy bias are fairly complex. First, we estimate the
underlying continuous distribution function from precise counts-in-cells
measurements assuming local Poisson sampling. Then a robust, non-parametric
inversion of the bias function is recovered from the comparison of the
cumulative distributions in simulated dark matter and galaxy catalogs.
Obtaining continuous statistics from the discrete counts is the most delicate
novel part of our recipe. It corresponds to a deconvolution of a (Poisson)
kernel. For this we present two alternatives: a model independent algorithm
based on Richardson-Lucy iteration, and a solution using a parametric skewed
lognormal model. We find that the latter is an excellent approximation for the
dark matter distribution, but the model independent iterative procedure is more
suitable for galaxies. Tests based on high resolution dark matter simulations
and corresponding mock galaxy catalogs show that we can reconstruct the
non-linear bias function down to highly non-linear scales with high precision
in the range of . As far as the stochasticity of the bias,
we have found a remarkably simple and accurate formula based on Poisson noise,
which provides an excellent approximation for the scatter around the mean
non-linear bias function. In addition we have found that redshift distortions
have a negligible effect on our bias reconstruction, therefore our recipe can
be safely applied to redshift surveys.Comment: 32 pages, 18 figures; submitted to Ap
Orbital and spin chains in ZnV2O4
Our powder inelastic neutron scattering data indicate that \zvo is a system
of spin chains that are three dimensionally tangled in the cubic phase above 50
K due to randomly occupied orbitals of V () ions. Below
50 K in the tetragonal phase, the chains become straight due to
antiferro-orbital ordering. This is evidenced by the characteristic wave vector
dependence of the magnetic structure factor that changes from symmetric to
asymmetric at the cubic-to-tetragonal transition
Staggered magnetism in LiVO at low temperatures probed by the muon Knight shift
We report on the muon Knight shift measurement in single crystals of LiV2O4.
Contrary to what is anticipated for the heavy-fermion state based on the Kondo
mechanism, the presence of inhomogeneous local magnetic moments is demonstrated
by the broad distribution of the Knight shift at temperatures well below the
presumed "Kondo temperature" ( K). Moreover, a significant
fraction ( %) of the specimen gives rise to a second component which
is virtually non-magnetic. These observations strongly suggest that the
anomalous properties of LiV2O4 originates from frustration of local magnetic
moments.Comment: 11 pages, 5 figures, sbmitted to J. Phys.: Cond. Mat
Bose-Einstein droplet in free space
We show that a droplet of a Bose-Einstein condensate can be dynamically
stabilized in free space by rapid oscillations of interatomic interactions
between attractive and repulsive through, e.g., the Feshbach resonance. Energy
dissipation, which is present in realistic situations, is found to play a
crucial role to suppress dynamical instabilities inherent in nonlinear
nonequilibrium systems.Comment: 5 pages, 5 figure
Evaluation of Effective Astrophysical S factor for Non-Resonant Reactions
We derived analytic formulas of the effective S astrophysical S factor,S^eff
for a non-resonant reaction of charged particles using a Taylor expension of
the astrophysical S factor and a uniform approximation.The formulas will be
able to generate generate more accurate approximation to S^eff than previous
ones
Criteria of off-diagonal long-range order in Bose and Fermi systems based on the Lee-Yang cluster expansion method
The quantum-statistical cluster expansion method of Lee and Yang is extended
to investigate off-diagonal long-range order (ODLRO) in one- and
multi-component mixtures of bosons or fermions. Our formulation is applicable
to both a uniform system and a trapped system without local-density
approximation and allows systematic expansions of one- and multi-particle
reduced density matrices in terms of cluster functions which are defined for
the same system with Boltzmann statistics. Each term in this expansion can be
associated with a Lee-Yang graph. We elucidate a physical meaning of each
Lee-Yang graph; in particular, for a mixture of ultracold atoms and bound
dimers, an infinite sum of the ladder-type Lee-Yang 0-graphs is shown to lead
to Bose-Einstein condensation of dimers below the critical temperature. In the
case of Bose statistics, an infinite series of Lee-Yang 1-graphs is shown to
converge and gives the criteria of ODLRO at the one-particle level.
Applications to a dilute Bose system of hard spheres are also made. In the case
of Fermi statistics, an infinite series of Lee-Yang 2-graphs is shown to
converge and gives the criteria of ODLRO at the two-particle level.
Applications to a two-component Fermi gas in the tightly bound limit are also
made.Comment: 21 pages, 10 figure
X-ray Dust Scattering at Small Angles: The Complete Halo around GX13+1
The exquisite angular resolution available with Chandra should allow
precision measurements of faint diffuse emission surrounding bright sources,
such as the X-ray scattering halos created by interstellar dust. However, the
ACIS CCDs suffer from pileup when observing bright sources, and this creates
difficulties when trying to extract the scattered halo near the source. The
initial study of the X-ray halo around GX13+1 using only the ACIS-I detector
done by Smith, Edgar & Shafer (2002) suffered from a lack of sensitivity within
50'' of the source, limiting what conclusions could be drawn.
To address this problem, observations of GX13+1 were obtained with the
Chandra HRC-I and simultaneously with the RXTE PCA. Combined with the existing
ACIS-I data, this allowed measurements of the X-ray halo between 2-1000''.
After considering a range of dust models, each assumed to be smoothly
distributed with or without a dense cloud along the line of sight, the results
show that there is no evidence in this data for a dense cloud near the source,
as suggested by Xiang et al. (2005). Finally, although no model leads to
formally acceptable results, the Weingartner & Draine (2001) and nearly all of
the composite grain models from Zubko, Dwek & Arendt (2004) give poor fits.Comment: 8 pages, 6 figures, accepted for publication in Ap
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