194 research outputs found
Variational Monte Carlo study of pentaquark states in a correlated quark model
Accurate numerical solution of the five-body Schrodinger equation is effected
via variational Monte Carlo in a correlated quark model. The spectrum is
assumed to exhibit a narrow resonance with strangeness S=+1. A fully
antisymmetrized and pair-correlated five-quark wave function is obtained for
the assumed non-relativistic Hamiltonian which has spin, isospin, and color
dependent pair interactions and many-body confining terms which are fixed by
the non-exotic spectra. Gauge field dynamics are modeled via flux tube exchange
factors. The energy determined for the ground states with spin-parity 1/2-
(1/2+) is 2.22 GeV (2.50 GeV). A lower energy negative parity state is
consistent with recent lattice results.Comment: 3 pages, PANIC05 conference proceeding
Effect of collisions on neutrino flavor inhomogeneity in a dense neutrino gas
We investigate the stability, with respect to spatial inhomogeneity, of a
two-dimensional dense neutrino gas. The system exhibits growth of seed
inhomogeneity due to nonlinear coherent neutrino self-interactions. In the
absence of incoherent collisional effects, we observe a dependence of this
instability growth rate on the neutrino mass spectrum: the normal neutrino mass
hierarchy exhibits spatial instability over a larger range of neutrino number
density compared to that of the inverted case. We further consider the effect
of elastic incoherent collisions of the neutrinos with a static background of
heavy, nucleon-like scatterers. At small scales, the growth of flavor
instability can be suppressed by collisions. At large length scales we find,
perhaps surprisingly, that for inverted neutrino mass hierarchy incoherent
collisions fail to suppress flavor instabilities, independent of the coupling
strength.Comment: 10 pages, 6 figures Version accepted in PLB. Minor changes. Title
change
Spin asymmetries for confined Dirac particles
We study the Bjorken `x' (or equivalently Nachtmann `xi') dependence of the
virtual photon spin asymmetry in polarized deep inelastic scattering of
electrons from hadrons. We use an exactly solved relativistic potential model
of the hadron, treating the constituents as independent massless Dirac
particles confined to an infinitely massive force center. The importance of
including the p-wave components of the Dirac wave function is demonstrated.
Comparisons are made to the observed data on the proton by taking into account
the observed flavor dependence of the valence quark distribution functions.Comment: 4 pages, 4 figues; submitted to Phys. Lett.
Final state interaction contribution to the response of confined relativistic particles
We report studies of the response of a massless particle confined by a
potential. At large momentum transfer q it exhibits \tilde{y} or equivalently
Nachtmann \xi scaling, and acquires a constant width independent of q. This
width has a contribution from the final state interactions of the struck
particle, which persists in the q->\infty limit. The width of the response
predicted using plane wave impulse approximation is smaller because of the
neglect of final state interactions in that approximation. However, the exact
response may be obtained by folding the approximate response with a function
representing final state interaction effects. We also study the response
obtained from the momentum distribution assuming that the particle is on the
energy shell both before and after being struck. Quantitative results are
presented for the special case of a linear confining potential. In this case
the response predicted with the on-shell approximation has correct values for
the total strength, mean energy and width, however its shape is wrong.Comment: 11 pages, 3 figures, submitted to Phys. Rev.
Unified Chew-Mandelstam SAID analysis of pion photoproduction data
A unified description of single-pion photoproduction data, together with
pion- and eta-hadroproduction data, has been achieved in a Chew-Mandelstam
parametrization which is consistent with unitarity at the two-body level.
Energy-dependent and single-energy partial wave analyses of pion
photoproduction data have been performed and compared to previous SAID fits and
multipoles from the Mainz and Bonn-Gatchina groups.Comment: 11 pages, 9 figures, and 2 table
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