1,374 research outputs found
The radial defocusing energy-supercritical cubic nonlinear wave equation in R^{1+5}
In this work, we consider the energy-supercritical defocusing cubic nonlinear
wave equation in dimension d=5 for radially symmetric initial data. We prove
that an a priori bound in the critical space implies global well-posedness and
scattering. The main tool that we use is a frequency localized version of the
classical Morawetz inequality, inspired by recent developments in the study of
the mass and energy critical nonlinear Schr\"odinger equation.Comment: AMS Latex, 20 page
Formation of interstellar SH from vibrationally excited H: Quantum study of S + H SH + H reactions and inelastic collisions
The rate constants for the formation, destruction, and collisional excitation
of SH are calculated from quantum mechanical approaches using two new
SH potential energy surfaces (PESs) of and electronic
symmetry. The PESs were developed to describe all adiabatic states correlating
to the SH () + H() channel. The formation of SH
through the S + H reaction is endothermic by 9860 K, and
requires at least two vibrational quanta on the H molecule to yield
significant reactivity. Quasi-classical calculations of the total formation
rate constant for H() are in very good agreement with the quantum
results above 100K. Further quasi-classical calculations are then performed for
, 4, and 5 to cover all vibrationally excited H levels significantly
populated in dense photodissociation regions (PDR). The new calculated
formation and destruction rate constants are two to six times larger than the
previous ones and have been introduced in the Meudon PDR code to simulate the
physical and illuminating conditions in the Orion bar prototypical PDR. New
astrochemical models based on the new molecular data produce four times larger
SH column densities, in agreement with those inferred from recent ALMA
observations of the Orion bar.Comment: 8 pages, 7 figure
d_{x^2-y^2} Symmetry and the Pairing Mechanism
An important question is if the gap in the high temperature cuprates has
d_{x^2-y^2} symmetry, what does that tell us about the underlying interaction
responsible for pairing. Here we explore this by determining how three
different types of electron-phonon interactions affect the d_{x^2-y^2} pairing
found within an RPA treatment of the 2D Hubbard model. These results imply that
interactions which become more positive as the momentum transfer increases
favor d_{x^2-y^2} pairing in a nearly half-filled band.Comment: 9 pages and 2 eps figs, uses revtex with epsf, in press, PR
Quantum Monte Carlo study of a nonmagnetic impurity in the two-dimensional Hubbard model
In order to investigate the effects of nonmagnetic impurities in strongly
correlated systems, Quantum Monte Carlo (QMC) simulations have been carried out
for the doped two-dimensional Hubbard model with one nonmagnetic impurity.
Using a bare impurity potential which is onsite and attractive, magnetic and
single-particle properties have been calculated. The QMC results show that
giant oscillations develop in the Knight shift response around the impurity
site due to the short-range antiferromagnetic correlations. These results are
useful for interpreting the NMR data on Li and Zn substituted layered cuprates.Comment: 10 pages, 7 figure
Quasiparticle Dispersion of the 2D Hubbard Model: From an Insulator to a Metal
On the basis of Quantum-Monte-Carlo results the evolution of the spectral
weight of the two-dimensional Hubbard model is studied from
insulating to metallic behavior. As observed in recent photoemission
experiments for cuprates, the electronic excitations display essentially
doping-independent features: a quasiparticle-like dispersive narrow band of
width of the order of the exchange interaction and a broad valence- and
conduction-band background. The continuous evolution is traced back to one and
the same many-body origin: the doping-dependent antiferromagnetic spin-spin
correlation.Comment: 11 pages, REVtex, 4 figures (in uuencoded postscript format
Anisotropy on the Fermi Surface of the Two-Dimensional Hubbard Model
We investigate anisotropic charge fluctuations in the two-dimensional Hubbard
model at half filling. By the quantum Monte Carlo method, we calculate a
momentum-resolved charge compressibility , which shows effects of an infinitesimal doping. At the temperature
, shows peak structure at the points along the line. A similar peak
structure is reproduced in the mean-filed calculation for the d-wave pairing
state or the staggered flux state.Comment: 5 pages, 3 figures, figures and presentation are modifie
Theory of spin and charge fluctuations in the Hubbard model
A self-consistent theory of both spin and charge fluctuations in the Hubbard
model is presented. It is in quantitative agreement with Monte Carlo data at
least up to intermediate coupling . It includes both
short-wavelength quantum renormalization effects, and long-wavelength thermal
fluctuations which can destroy long-range order in two dimensions. This last
effect leads to a small energy scale, as often observed in high temperature
superconductors. The theory is conserving, satisfies the Pauli principle and
includes three-particle correlations necessary to account for the incipient
Mott transition.Comment: J1K 2R1 10 pages, Revtex 3.0, 4 uuencoded postscript figures, report#
CRPS-93-4
d_{x^2-y^2}-wave superconductivity and the Hubbard model
The numerical studies of d_{x^2-y^2}-wave pairing in the two-dimensional (2D)
and the 2-leg Hubbard models are reviewed. For this purpose, the results
obtained from the determinantal Quantum Monte Carlo and the density-matrix
renormalization-group calculations are presented. These are calculations which
were motivated by the discovery of the high-T_c cuprates. In this review, the
emphasis is placed on the microscopic many-body processes which are responsible
for the d_{x^2-y^2}-wave pairing correlations observed in the 2D and the 2-leg
Hubbard models. In order to gain insight into these processes, the results on
the effective pairing interaction as well as the magnetic, density and the
single-particle excitations will be reviewed. In addition, comparisons will be
made with the other numerical approaches to the Hubbard model and the numerical
results on the t-J model. The results reviewed here indicate that an effective
pairing interaction which is repulsive at (pi,pi) momentum transfer and
enhanced single-particle spectral weight near the (pi,0) and (0,pi) points of
the Brillouin zone create optimum conditions for d_{x^2-y^2}-wave pairing.
These are two effects which act to enhance the d_{x^2-y^2}-wave pairing
correlations in the Hubbard model. Finding additional ways is an active
research problem.Comment: 85 pages, 63 figures, to appear in Advances in Physics, vol. 51, no.
6 (2002
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