2,186 research outputs found
Why Hybrid Meson Coupling to Two S-wave Mesons is Suppressed
We introduce strong interaction selection rules for the two-body decay and
production of hybrid and conventional mesons coupling to two S-wave hybrid or
conventional mesons. The rules arise from symmetrization in states in the limit
of non-relativistically moving quarks. The conditions under which hybrid
coupling to S-wave states is suppressed are determined by the rules, and the
nature of their breaking is indicated.Comment: 9 pages, LaTeX, 1 eps figures, uses epsf. Minor modifications, Title
chang
Using pi_2(1670) -> b_1(1235) pi to Constrain Hadronic Models
We show that current analyses of experimental data indicate that the strong
decay mode pi_2 -> b_1 pi is anomalously small. Non-relativistic quark models
with spin-1 quark pair creation, such as ^3P_0, ^3S_1 and ^3D_1 models, as well
as instanton and lowest order one-boson (in this case pi) emission models, can
accommodate the analyses of experimental data, because of a quark-spin
selection rule. Models and effects that violate this selection rule, such as
higher order one-boson emission models, as well as mixing with other Fock
states, may be constrained by the small pi_2 -> b_1 pi decay. This can provide
a viability check on newly proposed decay mechanisms. We show that for mesons
made up of a heavy quark and anti-quark, the selection rule is exact to all
orders of Quantum Chromodynamics (QCD) perturbation theory.Comment: 11 pages, LaTeX, 3 encapsulated Postscript figures, small change
Spitzer Mapping of PAHs and H2 in Photodissociation Regions
The mid-infrared (MIR) spectra of dense photodissociation regions (PDRs) are
typically dominated by emission from polycyclic aromatic hydrocarbons (PAHs)
and the lowest pure rotational states of molecular hydrogen (H2); two species
which are probes of the physical properties of gas and dust in intense UV
radiation fields. We utilize the high angular resolution of the Infrared
Spectrograph on the Spitzer Space Telescope to construct spectral maps of the
PAH and H2 features for three of the best studied PDRs in the galaxy, NGC 7023,
NGC 2023 and IC 63. We present spatially resolved maps of the physical
properties, including the H2 ortho-to-para ratio, temperature, and G_o/n_H. We
also present evidence for PAH dehydrogenation, which may support theories of H2
formation on PAH surfaces, and a detection of preferential self-shielding of
ortho-H2. All PDRs studied exhibit average temperatures of ~500 - 800K, warm H2
column densities of ~10^20 cm^-2, G_o/n_H ~ 0.1 - 0.8, and ortho-to-para ratios
of ~ 1.8. We find that while the average of each of these properties is
consistent with previous single value measurements of these PDRs, when
available, the addition of spatial resolution yields a diversity of values with
gas temperatures as high as 1500 K, column densities spanning ~ 2 orders of
magnitude, and extreme ortho-to-para ratios of 3.Comment: 14 figure
Configuration mixing in Pb : band structure and electromagnetic properties
In the present paper, we carry out a detailed analysis of the presence and
mixing of various families of collective bands in Pb. Making use of the
interacting boson model, we construct a particular intermediate basis that can
be associated with the unperturbed bands used in more phenomenological studies.
We use the E2 decay to construct a set of collective bands and discuss in
detail the B(E2)-values. We also perform an analysis of these theoretical
results (Q, B(E2)) to deduce an intrinsic quadrupole moment and the associated
quadrupole deformation parameter, using an axially deformed rotor model.Comment: submitted to pr
Hybrid Meson Decay Phenomenology
The phenomenology of a newly developed model of hybrid meson decay is
developed. The decay mechanism is based on the heavy quark expansion of QCD and
the strong coupling flux tube picture of nonperturbative glue. A comprehensive
list of partial decay widths of a wide variety of light, , ,
and hybrid mesons is presented. Results which appear approximately
universal are highlighted along with those which distinguish different hybrid
decay models. Finally, we examine several interesting hybrid candidates in
detail.Comment: 37 pages, 2 figures, 6 tables, Revte
Global fire activity patterns (1996-2006) and climatic influence: an analysis using World Fire Atlas
Vegetation fires have been acknowledged as an environmental
process of global scale, which affects the chemical
composition of the troposphere, and has profound ecological
and climatic impacts. However, considerable uncertainty
remains, especially concerning intra and inter-annual
variability of fire incidence. The main goals of our globalscale
study were to characterise spatial-temporal patterns of
fire activity, to identify broad geographical areas with similar
vegetation fire dynamics, and to analyse the relationship
between fire activity and the El NiËno-Southern Oscillation.
This study relies on 10 years (mid 1996âmid
2006) of screened European Space Agency World Fire Atlas
(WFA) data, obtained from Along Track Scanning Radiometer
(ATSR) and Advanced ATSR (AATSR) imagery.
Empirical Orthogonal Function analysis was used to reduce
the dimensionality of the dataset. Regions of homogeneous
fire dynamics were identified with cluster analysis, and interpreted
based on their eco-climatic characteristics. The
impact of 1997â1998 El NiËno is clearly dominant over the
study period, causing increased fire activity in a variety of
regions and ecosystems, with variable timing. Overall, this
study provides the first global decadal assessment of spatialtemporal
fire variability and confirms the usefulness of the
screened WFA for global fire ecoclimatology researc
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