262 research outputs found
A practical parametrization for line shapes of near-threshold states
Numerous quarkonium(like) states lying near -wave thresholds are observed
experimentally. We propose a self-consistent approach to these near-threshold
states compatible with unitarity and analyticity. The underlying
coupled-channel system includes a bare pole and an arbitrary number of elastic
and inelastic channels treated fully nonperturbatively. The resulting
analytical parametrization is ideally suited for a combined analysis of the
data available in various channels that is exemplified by an excellent overall
description of the data for the charged and states.Comment: LaTeX2e, 5 pages, 1 figure, typos corrected, version published in
Phys. Rev. Let
Nonlocality of nucleon interaction and an anomalous off shell behavior of the two-nucleon amplitudes
The problem of the ultraviolet divergences that arise in describing the
nucleon dynamics at low energies is considered. By using the example of an
exactly solvable model it is shown that after renormalization the interaction
generating nucleon dynamics is nonlocal in time. Effects of such nonlocality on
low-energy nucleon dynamics are investigated. It is shown that nonlocality in
time of nucleon-nucleon interactions gives rise to an anomalous off-shell
behavior of the two-nucleon amplitudes that have significant effects on the
dynamics of many-nucleon systems.Comment: 9 pages, 4 figures, ReVTeX
Interplay of quark and meson degrees of freedom in near-threshold states: A practical parametrisation for line shapes
We propose a practical parametrisation for the line shapes of near-threshold
states compatible with all requirements of unitarity and analyticity. The
coupled-channel system underlying the proposed parametrisation includes bare
poles and an arbitrary number of elastic and inelastic channels treated fully
nonperturbatively. The resulting formulae are general enough to be used for a
simultaneous analysis of the data in all available production and decay
channels of the (system of) state(s) under consideration for a quite wide class
of reactions. As an example, we fit the experimental data currently available
for several decay channels for the charged states in the
spectrum of bottomonia and find a good overall description of the data. We find
the present data to be consistent with the as a virtual state and
with the as a resonance, both residing very close to the
and threshold, respectively.Comment: LaTeX2e, 19 pages, 10 figures, version published in Phys.Rev.
Hamiltonian approach to the bound state problem in QCD_2
Bosonization of the two-dimensional QCD in the large N_C limit is performed
in the framework of Hamiltonian approach in the Coulomb gauge. The generalized
Bogoliubov transformation is applied to diagonalize the Hamiltonian in the
bosonic sector of the theory, and the composite operators creating/annihilating
bosons are obtained in terms of dressed quark operators. The bound state
equation is reconstructed as a result of the generalized Bogoliubov
transformation, and the form of its massless solution, chiral pion, is found
explicitly. Chiral properties of the theory are discussed.Comment: 9 pages, LaTeX2
QCD string in light-light and heavy-light mesons
The spectra of light-light and heavy-light mesons are calculated within the
framework of the QCD string model, which is derived from QCD in the Wilson loop
approach. Special attention is payed to the proper string dynamics that allows
us to reproduce the straight-line Regge trajectories with the inverse slope
being 2\pi\sigma for light-light and twice as small for heavy-light mesons. We
use the model of the rotating QCD string with quarks at the ends to calculate
the masses of several light-light mesons lying on the lowest Regge trajectories
and compare them with the experimental data as well as with the predictions of
other models. The masses of several low-lying orbitally and radially excited
heavy--light states in the D, D_s, B, and B_s meson spectra are calculated in
the einbein (auxiliary) field approach, which has proven to be rather accurate
in various calculations for relativistic systems. The results for the spectra
are compared with the experimental and recent lattice data. It is demonstrated
that an account of the proper string dynamics encoded in the so-called string
correction to the interquark interaction leads to an extra negative
contribution to the masses of orbitally excited states that resolves the
problem of the identification of the D(2637) state recently claimed by the
DELPHI Collaboration. For the heavy-light system we extract the constants
\bar\Lambda, \lambda_1, and \lambda_2 used in Heavy Quark Effective Theory
(HQET) and find good agreement with the results of other approaches.Comment: RevTeX, 42 pages, 7 tables, 7 EPS figures, uses epsfig.sty, typos
corrected, to appear in Phys.Rev.
A Sensitivity Study on the Effects of Particle Chemistry, Asphericity and Size on the Mass Extinction Efficiency of Mineral Dust in the Earth's Atmosphere: From the Near to Thermal IR
To determine a plausible range of mass extinction efficiencies (MEE) of terrestrial atmospheric dust from the near to thermal IR, sensitivity analyses are performed over an extended range of dust microphysical and chemistry perturbations. The IR values are subsequently compared to those in the near-IR, to evaluate spectral relationships in their optical properties. Synthesized size distributions consistent with measurements, model particle size, while composition is defined by the refractive indices of minerals routinely observed in dust, including the widely used OPAC/Hess parameterization. Single-scattering properties of representative dust particle shapes are calculated using the T-matrix, Discrete Dipole Approximation and Lorenz-Mie light-scattering codes. For the parameterizations examined, MEE ranges from nearly zero to 1.2 square meters per gram, with the higher values associated with non-spheres composed of quartz and gypsum. At near-IR wavelengths, MEE for non-spheres generally exceeds those for spheres, while in the thermal IR, shape-induced changes in MEE strongly depend on volume median diameter (VMD) and wavelength, particularly for MEE evaluated at the mineral resonant frequencies. MEE spectral distributions appear to follow particle geometry and are evidence for shape dependency in the optical properties. It is also shown that non-spheres best reproduce the positions of prominent absorption peaks found in silicates. Generally, angular particles exhibit wider and more symmetric MEE spectral distribution patterns from 8-10 micrometers than those with smooth surfaces, likely due to their edge-effects. Lastly, MEE ratios allow for inferring dust optical properties across the visible-IR spectrum. We conclude the MEE of dust aerosol are significant for the parameter space investigated, and are a key component for remote sensing applications and the study of direct aerosol radiative effects
Laser-driven 1st order spin reorientation and Verwey phase transitions in the magnetite FeO beyond the range of thermodynamic equilibrium
Ultrafast photo-induced phase transitions occurring under the impact of
femtosecond laser pulses provide versatile opportunities to switch solids
between distinctly-different crystalline, electronic, and spin states and thus
modify their functional properties in a significant manner. In this paper, we
report on the laser-induced spin reorientation and Verwey phase transitions in
a ferrimagnetic single crystalline magnetite FeO. Using femtosecond
optical and magneto-optical pump-probe techniques, we define the range of
initial sample temperatures and laser fluences when partial or complete
photo-induced phase transitions occur from a monoclinic insulating to a cubic
metallic state with concomitant switching of magnetic anisotropy from the
uniaxial to the cubic one. We thus reveal a connection between these phase
transitions when driven by femtosecond laser pulses. Using transient linear and
quadratic magneto-optical effects, we examine magnetization dynamics launched
by the magnetic anisotropy axis switching, and unveil the presence of the
domains undergoing the laser-induced phase transitions even below the
established thershold fluence for the transitions, as well as when the material
is initially in the cubic phase. This is the manifestation of the 1st order of
these laser-induced phase transitions beyond the range of thermodynamic
equilibrium.Comment: 9 pages, 5 figure, 1 supplemental materia
Magnetoelectric Effect and Spontaneous Polarization in HoFe(BO) and HoNdFe(BO)
The thermodynamic, magnetic, dielectric, and magnetoelectric properties of
HoFe(BO) and HoNdFe(BO) are
investigated. Both compounds show a second order Ne\'{e}l transition above 30 K
and a first order spin reorientation transition below 10 K.
HoFe(BO) develops a spontaneous electrical polarization below the
Ne\'{e}l temperature (T) which is diminished in external magnetic fields.
No magnetoelectric effect could be observed in HoFe(BO). In
contrast, the solid solution HoNdFe(BO) exhibits
both, a spontaneous polarization below T and a magnetoelectric effect at
higher fields that extends to high temperatures. The superposition of
spontaneous polarization, induced by the internal magnetic field in the ordered
state, and the magnetoelectric polarizations due to the external field results
in a complex behavior of the total polarization measured as a function of
temperature and field.Comment: 12 pages, 15 figure
WRF-Chem simulation of aerosol seasonal variability in the San Joaquin Valley
WRF-Chem simulations of aerosol seasonal variability in the San Joaquin
Valley (SJV), California, are evaluated by satellite and in situ
observations. Results show that the WRF-Chem model successfully captures the
distribution and magnitude of and variation in SJV aerosols during the cold
season. However, aerosols are not well represented in the warm season.
Aerosol simulations in urban areas during the cold season are sensitive to
model horizontal resolution, with better simulations at 4 km resolution than
at 20 km resolution, mainly due to inhomogeneous distribution of
anthropogenic emissions and precipitation that is represented better in the 4 km
simulation. In rural areas, the model sensitivity to grid size is rather
small. Our observational analysis reveals that dust is a primary contributor
to aerosols in the SJV, especially during the warm season. Aerosol
simulations in the warm season are sensitive to the parameterization of dust
emission in WRF-Chem. The GOCART (Goddard Global Ozone Chemistry Aerosol
Radiation and Transport) dust scheme produces very little dust in the SJV,
while the DUSTRAN (DUST TRANsport model) scheme overestimates dust emission.
Vertical mixing of aerosols is not adequately represented in the model based
on CALIPSO (Cloud-Aerosol Lidar and Infrared pathfinder Satellite
Observation) aerosol extinction profiles. Improved representation of dust
emission and vertical mixing in the boundary layer is needed for better
simulations of aerosols during the warm season in the SJV.</p
Comment on the proper QCD string dynamics in a heavy-light system
The string correction to the inter-quark interaction at large distances is
derived using the field theory approach to a heavy-light quark-antiquark system
in the modified Fock-Schwinger gauge.Comment: LaTeX2e, 6 pages, no figures, to appear in JETP Let
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