59,995 research outputs found
Real photons produced from photoproduction in collisions
We calculate the production of real photons originating from the
photoproduction in relativistic collisions. The
Weizscker-Williams approximation in the photoproduction is
considered. Numerical results agree with the experimental data from
Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC). We find
that the modification of the photoproduction is more prominent in large
transverse momentum region.Comment: 2 figure
Renormalization Group Study of the Electron-phonon Interaction in the High Tc Cuprates
We generalize the numerical renormalization group scheme to study the
phonon-mediated retarded interactions in the high Tc cuprates. We find that
three sets of phonon-mediated retarded quasiparticle scatterings grow under RG
flow. These scatterings share the following common features: 1) the initial and
final quasiparticle momenta are in the antinodal regions, and 2) the scattering
amplitudes have a symmetry. All three sets of retarded interaction
are driven to strong coupling by the magnetic fluctuations around .
After growing strong, these retarded interaction will trigger density wave
orders with d-wave symmetry. However, due to the d-wave form factor they will
leave the nodal quasiparticle unaffected. We conclude that the main effect of
electron-phonon coupling in the cuprates is to promote these density wave
orders.Comment: 4 pages, 3 figures, references added, added more details about
others' previous studie
On Convergence of Epanechnikov Mean Shift
Epanechnikov Mean Shift is a simple yet empirically very effective algorithm
for clustering. It localizes the centroids of data clusters via estimating
modes of the probability distribution that generates the data points, using the
`optimal' Epanechnikov kernel density estimator. However, since the procedure
involves non-smooth kernel density functions, the convergence behavior of
Epanechnikov mean shift lacks theoretical support as of this writing---most of
the existing analyses are based on smooth functions and thus cannot be applied
to Epanechnikov Mean Shift. In this work, we first show that the original
Epanechnikov Mean Shift may indeed terminate at a non-critical point, due to
the non-smoothness nature. Based on our analysis, we propose a simple remedy to
fix it. The modified Epanechnikov Mean Shift is guaranteed to terminate at a
local maximum of the estimated density, which corresponds to a cluster
centroid, within a finite number of iterations. We also propose a way to avoid
running the Mean Shift iterates from every data point, while maintaining good
clustering accuracies under non-overlapping spherical Gaussian mixture models.
This further pushes Epanechnikov Mean Shift to handle very large and
high-dimensional data sets. Experiments show surprisingly good performance
compared to the Lloyd's K-means algorithm and the EM algorithm.Comment: AAAI 201
Numerical Study of Quantum Hall Bilayers at Total Filling : A New Phase at Intermediate Layer Distances
We study the phase diagram of quantum Hall bilayer systems with total filing
of the lowest Landau level as a function of layer distances
. Based on numerical exact diagonalization calculations, we obtain three
distinct phases, including an exciton superfluid phase with spontaneous
interlayer coherence at small , a composite Fermi liquid at large , and
an intermediate phase for ( is the magnetic length). The
transition from the exciton superfluid to the intermediate phase is identified
by (i) a dramatic change in the Berry curvature of the ground state under
twisted boundary conditions on the two layers; (ii) an energy level crossing of
the first excited state. The transition from the intermediate phase to the
composite Fermi liquid is identified by the vanishing of the exciton superfluid
stiffness. Furthermore, from our finite-size study, the energy cost of
transferring one electron between the layers shows an even-odd effect and
possibly extrapolates to a finite value in the thermodynamic limit, indicating
the enhanced intralayer correlation. Our identification of an intermediate
phase and its distinctive features shed new light on the theoretical
understanding of the quantum Hall bilayer system at total filling .Comment: 5 pages, 3 figures (main text); 5 pages, 4 figures (supplementary
material); to be published in PR
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