134,276 research outputs found
The role of components in the N(1440) resonance
The role of 5-quark components in the pion and electromagnetic decays and
transition form factors of the N(1440) is explored. The
components, where the 4-quark subsystem has the flavor-spin symmetries
and , which are expected to have
the lowest energy of all configurations, are considered in detail
with a nonrelativistic quark model. The matrix elements between the 5-quark
components of the N(1440) and the nucleon, , play a
minor role in these decays, while the transition matrix elements and that involve quark antiquark annihilation are very
significant. Both for the electromagnetic and strong decay the change from the
valence quark model value is dominated by the confinement triggered
annihilation transitions. In the case of pion decay the calculated decay width
is enhanced substantially both by the direct and also by the
confinement triggered transitions. Agreement with the
empirical value for the pion decay width may be reached with a 30%
component in the N(1440).Comment: 23 pages revte
Lattice Boltzmann modeling of multiphase flows at large density ratio with an improved pseudopotential model
Owing to its conceptual simplicity and computational efficiency, the
pseudopotential multiphase lattice Boltzmann (LB) model has attracted
significant attention since its emergence. In this work, we aim to extend the
pseudopotential LB model to simulate multiphase flows at large density ratio
and relatively high Reynolds number. First, based on our recent work [Li et
al., Phys. Rev. E. 86, 016709 (2012)], an improved forcing scheme is proposed
for the multiple-relaxation-time pseudopotential LB model in order to achieve
thermodynamic consistency and large density ratio in the model. Next, through
investigating the effects of the parameter a in the Carnahan-Starling equation
of state, we find that the interface thickness is approximately proportional to
1/sqrt(a). Using a smaller a will lead to a wider interface thickness, which
can reduce the spurious currents and enhance the numerical stability of the
pseudopotential model at large density ratio. Furthermore, it is found that a
lower liquid viscosity can be gained in the pseudopotential model by increasing
the kinematic viscosity ratio between the vapor and liquid phases. The improved
pseudopotential LB model is numerically validated via the simulations of
stationary droplet and droplet oscillation. Using the improved model as well as
the above treatments, numerical simulations of droplet splashing on a thin
liquid film are conducted at a density ratio in excess of 500 with Reynolds
numbers ranging from 40 to 1000. The dynamics of droplet splashing is correctly
reproduced and the predicted spread radius is found to obey the power law
reported in the literature.Comment: 9 figures, 2 tables, accepted by Physical Review E (in press
Five-quark components in decay
Five-quark components in the are shown to
contribute significantly to decay through
quark-antiquark annihilation transitions. These involve the overlap between the
and components and may be triggered by the confining
interaction between the quarks. With a 10% admixture of five-quark
components in the the decay width can be larger by factors 2 - 3
over that calculated in the quark model with 3 valence quarks, depending on the
details of the confining interaction. The effect of transitions between the
components themselves on the calculated decay width is however
small. The large contribution of the quark-antiquark annihilation transitions
thus may compensate the underprediction of the width of the by
the valence quark model, once the contains
components with 10% probability.Comment: accepted versio
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