16586082
Momentum dependence of the rho - omega mixing amplitude in a hadronic model.
We calculate the momentum dependence of the [rho]-[omega] mixing amplitude in a purely hadronic model. The basic assumption of the model is that the mixing amplitude is generated by [ital N[bar N]] loops and thus driven entirely by the neutron-proton mass difference. The value of the amplitude at the [omega]-meson point is expressed in terms of only the [ital NN][omega] and [ital NN][rho] coupling constants. Using values for these couplings constrained by empirical two-nucleon data we obtain a value for the mixing amplitude in agreement with experiment. Extending these results to the spacelike region, we find a [rho]-[omega] contribution to the [ital NN] interaction that is strongly suppressed and opposite in sign relative to the conventional contribution obtained from using the constant on-shell value for the mixing amplitude.
119715243
Unquenching effects in the quark and gluon propagator
In this work we examine the fat-link irrelevant clover (FLIC) overlap quark propagator and the gluon propagator on both dynamical and quenched lattices. The tadpole-improved Luscher-Weisz gauge action is used in both cases. The dynamical gauge fields use the FLIC fermion action for the sea quark contribution. We observe that the presence of sea quarks causes a suppression of the mass function, quark renormalization function, and gluon dressing function in the infrared. The ultraviolet physics is unaffected.
16537962
Quark-gluon vertex in a momentum subtraction scheme
We compute the quark-gluon vertex in quenched QCD, in the Landau gauge using an off-shell mean-field O(a)-improved fermion action. The running coupling is calculated in an ‘asymmetric’ momentum subtraction scheme (MOM). We obtain a crude estimate for ΛMS = 170 ± 65 MeV, which is considerably lower than other determinations of this quantity. However, substantial systematic errors remain.
121820024
Can Schwinger-Dyson equations be solved independently of the regulator?
17365172
Heavy quark distribution functions in heavy baryons
Using the Bethe-Salpeter (B-S) equations for heavy baryons Lambda_Q, Sigma_Q, Xi_Q and Omega_Q (Q=b or c), which were established in previous work, we calculate the heavy quark distribution functions in these baryons. The numerical results indicate that these distribution functions have an obvious peak at some fraction, alpha_0, of the baryon's light-cone ``plus'' momentum component carried by the heavy quark, and that as m_Q becomes heavier this peak becomes sharper and closer to 1. The dependence of the distribution functions on various input parameters in the B-S model is also discussed. The results are seen to be qualitatively similar to an existing phenomenological model.
54954874
Stout-link smearing in lattice fermion actions
The properties of the momentum-space quark propagator in the Landau gauge are studied for the overlap quark action in quenched lattice QCD. Numerical calculations are performed over four ensembles of gauge configurations, where three are smeared using either 1, 3, or 6 sweeps of stout-link smearing. We calculate the nonperturbative wave-function renormalization function Z(p) and the nonperturbative mass function M(p) for a variety of bare quark masses. We find that the wave-function renormalization function is slightly sensitive to the number of stout-link smearing sweeps. For the mass function we find the effect of the stout-link smearing algorithm to be small for moderate to light bare quark masses. For a heavy bare quark mass we find a strong dependence on the number of smearing sweeps.
45418780
Multiparticle coherence calculations for synchrotron-radiation emission.
We have used Monte Carlo calculations to verify the classical electrodynamics result describing the multiparticle coherent enhancement at long wavelengths for synchrotron-radiation emission. In addition we show the derivation of the result that, for a bunch of electrons in a storage ring, the synchrotron-radiation emission has a multiparticle coherent enhancement that is given by the square of the Fourier transform of the longitudinal spatial distribution function of the electrons. The result has been verified for Gaussian and sinusoidal distributions. For a Gaussian distribution of particles in a bunch, this is seen to have an effect only at wavelengths close to the bunch length. For a sinusoidal distribution as in the transverse optical klystron, the enhancement can easily be seen to occur at one specific wavelength.