2,784 research outputs found
Second moment of the Husimi distribution as a measure of complexity of quantum states
We propose the second moment of the Husimi distribution as a measure of
complexity of quantum states. The inverse of this quantity represents the
effective volume in phase space occupied by the Husimi distribution, and has a
good correspondence with chaoticity of classical system. Its properties are
similar to the classical entropy proposed by Wehrl, but it is much easier to
calculate numerically. We calculate this quantity in the quartic oscillator
model, and show that it works well as a measure of chaoticity of quantum
states.Comment: 25 pages, 10 figures. to appear in PR
Inversionless gain in a three-level system driven by a strong field and collisions
Inversionless gain in a three-level system driven by a strong external field
and by collisions with a buffer gas is investigated. The mechanism of
populating of the upper laser level contributed by the collision transfer as
well as by relaxation caused by a buffer gas is discussed in detail. Explicit
formulae for analysis of optimal conditions are derived. The mechanism
developed here for the incoherent pump could be generalized to other systems.Comment: RevTeX, 9 pages, 4 eps figure
Semiquantum Chaos in the Double-Well
The new phenomenon of semiquantum chaos is analyzed in a classically regular
double-well oscillator model. Here it arises from a doubling of the number of
effectively classical degrees of freedom, which are nonlinearly coupled in a
Gaussian variational approximation (TDHF) to full quantum mechanics. The
resulting first-order nondissipative autonomous flow system shows energy
dependent transitions between regular behavior and semiquantum chaos, which we
monitor by Poincar\'e sections and a suitable frequency correlation function
related to the density matrix. We discuss the general importance of this new
form of deterministic chaos and point out the necessity to study open
(dissipative) quantum systems, in order to observe it experimentally.Comment: LaTeX, 25 pages plus 7 postscript figures. Replaced figure 3 with a
non-bitmapped versio
Moments of nucleon spin-dependent generalized parton distributions
We present a lattice measurement of the first two moments of the
spin-dependent GPD H-tilde(x,xi,t). From these we obtain the axial coupling
constant and the second moment of the spin-dependent forward parton
distribution. The measurements are done in full QCD using Wilson fermions. In
addition, we also present results from a first exploratory study of full QCD
using Asqtad sea and domain-wall valence fermions.Comment: Lattice2003(Theory), 3 pages, 3 figures, to appear in the Proceedings
of Lattice 200
First Evidence of -Dependence in the QCD Interquark Potential
We present a lattice calculation of the interquark potential between static
quarks in a ``full'' QCD simulation with 2 flavours of dynamical Wilson-quarks
at three intermediate sea-quark masses. We work at on lattice
size of with 100 configurations per sea-quark mass. We compare
the full QCD potential with its quenched counterpart at equal lattice spacing,
GeV, which is at the onset of the quenched scaling regime.
We find that the full QCD potential lies consistently below that of quenched
QCD. We see no evidence for string-breaking effects on these lattice volumes,
.Comment: 9 pages (1 tex file epsf-style + 6 ps-figures
Continuum Extrapolation of Moments of Nucleon Quark Distributions in Full QCD
Moments of light cone quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD at and using Wilson fermions on lattices. These results are combined with earlier calculations at using SESAM configurations to study the continuum limit
Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
We compute the Milky Way potential in different cold dark matter (CDM) based
models, and compare these with the modified Newtonian dynamics (MOND)
framework. We calculate the axis ratio of the potential in various models, and
find that isopotentials are less spherical in MOND than in CDM potentials. As
an application of these models, we predict the escape velocity as a function of
the position in the Galaxy. This could be useful in comparing with future data
from planned or already-underway kinematic surveys (RAVE, SDSS, SEGUE, SIM,
GAIA or the hypervelocity stars survey). In addition, the predicted escape
velocity is compared with the recently measured high proper motion velocity of
the Large Magellanic Cloud (LMC). To bind the LMC to the Galaxy in a MOND
model, while still being compatible with the RAVE-measured local escape speed
at the Sun's position, we show that an external field modulus of less than
is needed.Comment: Accepted for publication in MNRAS, 13 pages, 7 figures, 3 table
Supersonic water masers in 30 Doradus
We report on extremely high velocity molecular gas, up to -80 km/s relative
to the ambient medium, in the giant star-formation complex 30 Doradus in the
Large Magellanic Cloud (LMC), as observed in new 22 GHz H2O maser emission
spectra obtained with the Mopra radio telescope. The masers may trace the
velocities of protostars, and the observed morphology and kinematics indicate
that current star formation occurs near the interfaces of colliding
stellar-wind blown bubbles. The large space velocities of the protostars and
associated gas could result in efficient mixing of the LMC. A similar mechanism
in the Milky Way could seed the galactic halo with relatively young stars and
gas.Comment: 11 pages plus 1 PS and 1 EPS figure, uses AASTeX preprint style;
accepted for publication in Astrophysical Journal Letter
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