9,066 research outputs found
Production of the pentaquark in scattering
We study and processes
for both of the positive and negative parities of the . Employing
the effective chiral Lagrangians for the and interactions, we
calculate differential cross sections as well as total cross sections for the
and reactions. The total
cross sections for the positive-parity turn out to be approximately
ten times larger than those for the negative parity in the range of
the CM energy . The results are
rather sensitive to the mechanism of exchanges in the -- channel.Comment: 9 pages and 11 figure
Time-dependent coupled-cluster method for atomic nuclei
We study time-dependent coupled-cluster theory in the framework of nuclear
physics. Based on Kvaal's bi-variational formulation of this method [S. Kvaal,
arXiv:1201.5548], we explicitly demonstrate that observables that commute with
the Hamiltonian are conserved under time evolution. We explore the role of the
energy and of the similarity-transformed Hamiltonian under real and imaginary
time evolution and relate the latter to similarity renormalization group
transformations. Proof-of-principle computations of He-4 and O-16 in small
model spaces, and computations of the Lipkin model illustrate the capabilities
of the method.Comment: 10 pages, 9 pdf figure
Automatic Dimension Selection for a Non-negative Factorization Approach to Clustering Multiple Random Graphs
We consider a problem of grouping multiple graphs into several clusters using
singular value thesholding and non-negative factorization. We derive a model
selection information criterion to estimate the number of clusters. We
demonstrate our approach using "Swimmer data set" as well as simulated data
set, and compare its performance with two standard clustering algorithms.Comment: This paper has been withdrawn by the author due to a newer version
with overlapping content
SPEAR Far Ultraviolet Spectral Images of the Cygnus Loop
We present far-ultraviolet (FUV) spectral images, measured at C IV 1550, He
II 1640, Si IV+O IV] 1400, and O III] 1664, of the entire Cygnus Loop, observed
with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR)
instrument, also known as FIMS. The spatial distribution of FUV emission
generally corresponds with a limb-brightened shell, and is similar to optical,
radio and X-ray images. The features found in the present work include a
``carrot'', diffuse interior, and breakout features, which have not been seen
in previous FUV studies. Shock velocities of 140-160 km/s is found from a line
ratio of O IV] to O III], which is insensitive not only to resonance scattering
but also to elemental abundance. The estimated velocity indicates that the fast
shocks are widespread across the remnant. By comparing various line ratios with
steady-state shock models, it is also shown that the resonance scattering is
widespread.Comment: 13 pages, 3 figures, 1 table, accepted for publication in ApJ
Vector- and Pseudoscalar-baryon coupled channel systems
In this manuscript, I will report the details of our recent work on the
vector meson-baryon (VB) interaction, which we studied with the motivation of
finding dynamical generation of resonances in the corresponding systems. We
started our study by building a formalism based on the hidden local symmetry
and calculating the leading order contributions to the scattering equations by
summing the diagrams with: (a) a vector meson exchange in the t-channel (b) an
octet baryon exchange in the s-, u-channels and (c) a contact interaction
arising from the part of the vector meson-baryon Lagrangian which is related to
the anomalous magnetic moment of the baryons. We find the contribution from all
these sources, except the s-channel, to be important. The amplitudes obtained
by solving the coupled channel Bethe-Salpeter equations for the systems with
total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance
and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We
identify these resonances with (1900) , (2080) ,
(1700) , and (2090) , respectively.
We have further extended our study by including pseudoscalar meson-baryon
(PB) as the coupled channels of VB systems. For this, we obtain the PB
VB amplitudes by using the Kroll-Ruddermann term where,
considering the vector meson dominance phenomena, the photon is replaced by a
vector meson. The calculations done within this formalism reveal a very strong
coupling of the VB channels to the low-lying resonances like (1405)
and (1670), which can have important implications on certain reactions
producing them. In addition to this, we find that the effect of coupling the
higher mass states to the lighter channels is not restricted to increasing the
width of those states, it can be far more strong.Comment: Proceedings of the "DAE-BRNS Workshop on Hadron Physics" held in
Mumbai, India during October 31-November 04, 201
Solid-Liquid Phase Diagrams for Binary Metallic Alloys: Adjustable Interatomic Potentials
We develop a new approach to determining LJ-EAM potentials for alloys and use
these to determine the solid-liquid phase diagrams for binary metallic alloys
using Kofke's Gibbs-Duhem integration technique combined with semigrand
canonical Monte Carlo simulations. We demonstrate that it is possible to
produce a wide-range of experimentally observed binary phase diagrams (with no
intermetallic phases) by reference to the atomic sizes and cohesive energies of
the two elemental materials. In some cases, it is useful to employ a single
adjustable parameter to adjust the phase diagram (we provided a good choice for
this free parameter). Next, we perform a systematic investigation of the effect
of relative atomic sizes and cohesive energies of the elements on the binary
phase diagrams. We then show that this approach leads to good agreement with
several experimental binary phase diagrams. The main benefit of this approach
is not the accurately reproduction of experimental phase diagrams, but rather
to provide a method by which material properties can be continuously changed in
simulations studies. This is one of the keys to the use of atomistic
simulations to understand mechanisms and properties in a manner not available
to experiment
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