FULL QCD HADRON SPECTROSCOPY WITH 2 FLAVORS OF DYNAMIC KOGUT-SUSSKIND QUARKS ON THE LATTICE

A full lattice QCD simulation is carried out with two flavors of Kogut-Susskind staggered dynamical quarks using lattices of a size ranging from 4(4) to 20(4) at the gauge coupling constant beta = 6/g2 = 5.7 with the quark mass of m(q) = 0.01 and 0.02 in lattice units. Primary emphasis is given to the study of finite-lattice-size effects in the hadron mass spectrum. It is found that hadron masses suffer from substantial finite-size effects even for a lattice size of the order of 2 fm, showing the importance of a quantitative control of the effect for a comparison with the experimental spectrum at the accuracy of a few percent level. The finite-size correction is found to be well described by a power law in the lattice size, rather than an exponential form predicted by analytic formulas derived for point particles. It is suggested that the effect arises from the size of hadrons squeezed on a finite lattice. Finite-size effects on the realization of chiral symmetry are also studied. The behavior of the pion mass, the chiral condensate, and the mass splitting.between parity partners all support a spontaneous breakdown of chiral symmetry for a large lattice size. Prediction from chiral Lagrangians on the size dependence of the chiral condensate does not describe the simulation results well, however, at least for the quark mass employed for the present study. Calculation of the pion decay constant with various relations derived from current algebra and partial conservation of axial-vector current gives f(pi) = 94(8)-105(9) MeV, with a method-dependent uncertainty contained within 10%. An examination is also made of the question of the dependence of hadron masses on hadron operators. Meson masses are basically operator independent, while baryon masses exhibit some operator dependence, necessitating further studies to resolve systematic uncertainties of this origin in the determination of the hadron mass spectrum.