9,203 research outputs found
Excitonic and Quasiparticle Life Time Effects on Silicon Electron Energy Loss Spectrum from First Principles
The quasiparticle decays due to electron-electron interaction in silicon are
studied by means of first-principles all-electron GW approximation. The
spectral function as well as the dominant relaxation mechanisms giving rise to
the finite life time of quasiparticles are analyzed. It is then shown that
these life times and quasiparticle energies can be used to compute the complex
dielectric function including many-body effects without resorting to empirical
broadening to mimic the decay of excited states. This method is applied for the
computation of the electron energy loss spectrum of silicon. The location and
line shape of the plasmon peak are discussed in detail.Comment: 4 pages, 3 figures, submitted to PR
An SZ/X-ray galaxy cluster model and the X-ray follow-up of the Planck clusters
Sunyaev-Zel'dovich (SZ) cluster surveys will become an important cosmological
tool over next few years, and it will be essential to relate these new surveys
to cluster surveys in other wavebands. We present an empirical model of cluster
SZ and X-ray observables constructed to address this question and to motivate,
dimension and guide X-ray follow-up of SZ surveys. As an example application of
the model, we discuss potential XMM-Newton follow-up of Planck clusters.Comment: 4 pages, 5 figures. To appear in the proceedings of the XXXXIIIrd
Rencontres de Morion
Rigorous Bounds to Retarded Learning
We show that the lower bound to the critical fraction of data needed to infer
(learn) the orientation of the anisotropy axis of a probability distribution,
determined by Herschkowitz and Opper [Phys.Rev.Lett. 86, 2174 (2001)], is not
always valid. If there is some structure in the data along the anisotropy axis,
their analysis is incorrect, and learning is possible with much less data
points.Comment: 1 page, 1 figure. Comment accepted for publication in Physical Review
Letter
BEC-BCS crossover in an optical lattice
We present the microscopic theory for the BEC-BCS crossover of an atomic
Fermi gas in an optical lattice, showing that the Feshbach resonance underlying
the crossover in principle induces strong multiband effects. Nevertheless, the
BEC-BCS crossover itself can be described by a single-band model since it
occurs at magnetic fields that are relatively far away from the Feshbach
resonance. A criterion is proposed for the latter, which is obeyed by most
known Feshbach resonances in ultracold atomic gases.Comment: 4 pages, 3 figure
Zero-Temperature Properties of the Quantum Dimer Model on the Triangular Lattice
Using exact diagonalizations and Green's function Monte Carlo simulations, we
have studied the zero-temperature properties of the quantum dimer model on the
triangular lattice on clusters with up to 588 sites. A detailed comparison of
the properties in different topological sectors as a function of the cluster
size and for different cluster shapes has allowed us to identify different
phases, to show explicitly the presence of topological degeneracy in a phase
close to the Rokhsar-Kivelson point, and to understand finite-size effects
inside this phase. The nature of the various phases has been further
investigated by calculating dimer-dimer correlation functions. The present
results confirm and complement the phase diagram proposed by Moessner and
Sondhi on the basis of finite-temperature simulations [Phys. Rev. Lett. {\bf
86}, 1881 (2001)].Comment: 10 pages, 16 figure
Pressure-Induced Simultaneous Metal-Insulator and Structural-Phase Transitions in LiH: a Quasiparticle Study
A pressure-induced simultaneous metal-insulator transition (MIT) and
structural-phase transformation in lithium hydride with about 1% volume
collapse has been predicted by means of the local density approximation (LDA)
in conjunction with an all-electron GW approximation method. The LDA wrongly
predicts that the MIT occurs before the structural phase transition. As a
byproduct, it is shown that only the use of the generalized-gradient
approximation together with the zero-point vibration produces an equilibrium
lattice parameter, bulk modulus, and an equation of state that are in excellent
agreement with experimental results.Comment: 7 pages, 4 figures, submitted to Europhysics Letter
On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters
The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the
field and in rich galaxy clusters are contrasted by juxtaposing the build-up of
heavy metals in the universe inferred from observed star formation and
supernovae rate histories with data on the evolution of Fe abundances in the
intracluster medium (ICM). Models for the chemical evolution of Fe in these
environments are constructed, subject to observational constraints, for this
purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial
mass function (IMF) are consistent with observations in the field, cluster Fe
enrichment immediately tracks a rapid, top-heavy phase of star formation --
although transport of Fe into the ICM may be more prolonged and star formation
likely continues to redshifts <1. The source of this prompt enrichment is Type
II supernovae (SNII) yielding at least 0.1 solar masses per explosion (if the
SNIa rate normalization is scaled down from its value in the field according to
the relative number of candidate progenitor stars in the 3-8 solar mass range)
and/or SNIa explosions with short delay times associated with the rapid star
formation mode. Star formation is >3 times more efficient in rich clusters than
in the field, mitigating the overcooling problem in numerical cluster
simulations. Both the fraction of baryons cycled through stars, and the
fraction of the total present-day stellar mass in the form of stellar remnants,
are substantially greater in clusters than in the field.Comment: 51 pages including 26 figures and 2 tables, accepted for publication
in ApJ 5/4/0
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