42,122 research outputs found
Thermodynamical quantities of lattice full QCD from an efficient method
I extend to QCD an efficient method for lattice gauge theory with dynamical
fermions. Once the eigenvalues of the Dirac operator and the density of states
of pure gluonic configurations at a set of plaquette energies (proportional to
the gauge action) are computed, thermodynamical quantities deriving from the
partition function can be obtained for arbitrary flavor number, quark masses
and wide range of coupling constants, without additional computational cost.
Results for the chiral condensate and gauge action are presented on the
lattice at flavor number , 1, 2, 3, 4 and many quark masses and coupling
constants. New results in the chiral limit for the gauge action and its
correlation with the chiral condensate, which are useful for analyzing the QCD
chiral phase structure, are also provided.Comment: Latex, 11 figures, version accepted for publicatio
Theoretical modeling of spatial and temperature dependent exciton energy in coupled quantum wells
Motivated by a recent experiment of spatial and temperature dependent average
exciton energy distribution in coupled quantum wells [S. Yang \textit{et al.},
Phys. Rev. B \textbf{75}, 033311 (2007)], we investigate the nature of the
interactions in indirect excitons. Based on the uncertainty principle, along
with a temperature and energy dependent distribution which includes both
population and recombination effects, we show that the interplay between an
attractive two-body interaction and a repulsive three-body interaction can lead
to a natural and good account for the nonmonotonic temperature dependence of
the average exciton energy. Moreover, exciton energy maxima are shown to locate
at the brightest regions, in agreement with the recent experiments. Our results
provide an alternative way for understanding the underlying physics of the
exciton dynamics in coupled quantum wells.Comment: 8 pages, 5 figure
Pulsed THz radiation due to phonon-polariton effect in [110] ZnTe crystal
Pulsed terahertz (THz) radiation, generated through optical rectification
(OR) by exciting [110] ZnTe crystal with ultrafast optical pulses, typically
consists of only a few cycles of electromagnetic field oscillations with a
duration about a couple of picoseconds. However, it is possible, under
appropriate conditions, to generate a long damped oscillation tail (LDOT)
following the main cycles. The LDOT can last tens of picoseconds and its
Fourier transform shows a higher and narrower frequency peak than that of the
main pulse. We have demonstrated that the generation of the LDOT depends on
both the duration of the optical pulse and its central wavelength. Furthermore,
we have also performed theoretical calculations based upon the OR effect
coupled with the phonon-polariton mode of ZnTe and obtained theoretical THz
waveforms in good agreement with our experimental observation.Comment: 9 pages, 5 figure
Study of charm and beauty mass spectra, semileptonic decays of and in a phenomenological potential model
Using a non-relativistic potential model, we obtain the mass spectra,
leptonic decay constants, and parameters of the Isgur-Wise function for the
beauty and charm mesons. With the calculated quantities, we investigate purely
leptonic decays of , , , semileptonic decay modes and for three lepton
channels , and obtain the corresponding branching fractions. transitions are also studied. Next, we
apply the form factors for spin zero and spin one transitions of to
calculate the nonleptonic branching ratios of , where and stand for the vector meson and the
pseudoscalar meson, respectively. Our results are found to be in agreement with
those obtained in the experimental and theoretical results
Deformation and spallation of shocked Cu bicrystals with Σ3 coherent and symmetric incoherent twin boundaries
We perform molecular dynamics simulations of Cu bicrystals with two important grain boundaries (GBs), Σ3 coherent twin boundaries (CTB), and symmetric incoherent twin boundaries (SITB) under planar shock wave loading. It is revealed that the shock response (deformation and spallation) of the Cu bicrystals strongly depends on the GB characteristics. At the shock compression stage, elastic shock wave can readily trigger GB plasticity at SITB but not at CTB. The SITB can induce considerable wave attenuation such as the elastic precursor decay via activating GB dislocations. For example, our simulations of a Cu multilayer structure with 53 SITBs (∼1.5-μm thick) demonstrate a ∼80% elastic shock decay. At the tension stage, spallation tends to occur at CTB but not at SITB due to the high mobility of SITB. The SITB region transforms into a threefold twin via a sequential partial dislocation slip mechanism, while CTB preserves its integrity before spallation. In addition, deformation twinning is a mechanism for inducing surface step during shock tension stage. The drastically different shock response of CTB and SITB could in principle be exploited for, or benefit, interface engineering and materials design
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