24,047 research outputs found
Effect of higher orbital angular momenta in the baryon spectrum
We have performed a Faddeev calculation of the baryon spectrum for the chiral
constituent quark model including higher orbital angular momentum states. We
have found that the effect of these states is important, although a description
of the baryon spectrum of the same quality as the one given by including only
the lowest-order configurations can be obtained. We have studied the effect of
the pseudoscalar quark-quark interaction on the relative position of the
positive- and negative-parity excitations of the nucleon as well as the effect
of varying the strength of the color-magnetic interaction.Comment: 7 pages, 4 figures. To be published in Phys. Rev. C (November 2001
Quark Cluster Model Study of Isospin-Two Dibaryons
Based on a quark cluster model for the non-strange sector that reproduces
reasonably well the nucleon-nucleon system and the excitation of the
isobar, we generate a nucleon- interaction and present the predictions
for the several isospin two channels. The only attractive channels are
and , but not attractive enough to generate a resonance. If a resonance is
artificially generated and is required to have the observed experimental mass,
then our model predicts a width that agrees with the experimental result.Comment: 12 pages, 5 poscript figures available under request. To appear in
Phys. Rev.
On the variational homotopy perturbation method for nonlinear oscillators
In this paper we discuss a recent application of a variational homotopy
perturbation method to rather simple nonlinear oscillators . We show that the
main equations are inconsistent and for that reason the results may be of
scarce utility
and systems at threshold: II. The effect of D waves
Using the two-body interactions obtained from a chiral constituent quark
model we study all and states with I=0,1,2 and
J=1/2,3/2 at threshold, taking into account all three-body configurations with
S and D wave components. We constrain further the limits for the
spin-triplet scattering length a_{1/2,1}. Using the hypertriton binding energy
we find a narrow interval for the possible values of the
spin-singlet scattering length a_{1/2,0}. We found that the system
has a quasibound state in the (I,J) = (1,1/2) channel very near threshold with
a width of about 2.1 MeV.Comment: 19 pages, 4 tables, 6 figures. Accepted for publication in Phys. Rev.
Bulk viscosity and the conformal anomaly in the pion gas
We calculate the bulk viscosity of the massive pion gas within Unitarized
Chiral Perturbation Theory. We obtain a low temperature peak arising from
explicit conformal breaking due to the pion mass and another peak near the
critical temperature, dominated by the conformal anomaly through gluon
condensate terms. The correlation between bulk viscosity and conformal breaking
supports a recent QCD proposal. We discuss the role of resonances, heavier
states and large- counting.Comment: Revised version accepted in Phys.Rev.Lett. 4 pages, 3 figure
Does the quark cluster model predict any isospin two dibaryon resonance?
We analyze the possible existence of a resonance in the channel
with isospin two by means of nucleon- interactions based on the
constituent quark model. We solve the bound state and the scattering problem
using two different potentials, a local and a non-local one. The non-local
potential results to be the more attractive, although not enough to generate
the experimentally predicted resonance.Comment: 9 pages in Latex (revtex), 2 eps figures available under reques
A family of complex potentials with real spectrum
We consider a two-parameter non hermitean quantum-mechanical hamiltonian that
is invariant under the combined effects of parity and time reversal
transformation. Numerical investigation shows that for some values of the
potential parameters the hamiltonian operator supports real eigenvalues and
localized eigenfunctions. In contrast with other PT symmetric models, which
require special integration paths in the complex plane, our model is integrable
along a line parallel to the real axis.Comment: Six figures and four table
Discovery of a Small Central Disk of CO and HI in the Merger Remnant NGC 34
We present CO(1-0) and HI(21-cm) observations of the central region of the
wet merger remnant NGC 34. The Combined Array for Research in Millimeter-wave
Astronomy (CARMA) observations detect a regularly rotating disk in CO with a
diameter of 2.1 kpc and a total molecular hydrogen mass of (. The rotation curve of this gas disk rises steeply,
reaching maximum velocities at 1" (410 pc) from the center. Interestingly, HI
observations done with the Karl G. Jansky Very Large Array show that the
absorption against the central continuum has the exact same velocity range as
the CO in emission. This strongly suggests that the absorbing HI also lies
within 1" from the center, is mixed in and corotates with the molecular gas. A
comparison of HI absorption profiles taken at different resolutions (5"-45")
shows that the spectra at lower resolutions are less deep at the systemic
velocity. This provides evidence for HI emission in the larger beams, covering
the region from 1 kpc to 9 kpc from the center. The central rapidly rotating
disk was likely formed either during the merger or from fall-back material.
Lastly, the radio continuum flux of the central source at mm wavelengths
( mJy) is significantly higher than expected from an extrapolation
of the synchrotron spectrum, indicating the contribution of thermal free-free
emission from the central starburst.Comment: Accepted for publication in A
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