115237596
Calculations of charge-symmetry breaking in n-p elastic scattering
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.
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.
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.
121820024
Can Schwinger-Dyson equations be solved independently of the regulator?
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.
117027647
Astronomical Evidence for the Rapid Growth of Millimeter Sized Particles in Protoplanetary Disks
I summarize recent surveys of protoplanetary disks at millimeter wavelengths and show that the distribution of luminosity, equivalent to the mass in small dust grains, declines rapidly. This contrasts with statistics on the lifetime of disks from infrared observations and the high occurrence of planets from radial velocity and transit surveys. I suggest that these disparate results can be reconciled if most of the dust in a disk is locked up in millimeter and larger sized particles within about 2 Myr. This statistical result on disk evolution agrees with detailed modeling of a small number of individual disks and with cosmochemical measurements of rapid planetesimal formation.