The Light Hadron Spectrum and Decay Constants in Quenched Lattice QCD

We present results for light hadrons composed of both degenerate and non-degenerate quarks in quenched lattice QCD. We calculate masses and decay constants using 60 gauge configurations with an $O(a)$--improved fermion action at $\beta = 6.2$. Using the $\rho$ mass to set the scale, we find hadron masses within two to three standard deviations of the experimental values (given in parentheses): m_{K^*}=868\er{9}{8}~MeV (892~MeV), m_{\phi}=970\err{20}{10}~MeV (1020~MeV), m_N=820\err{90}{60}~MeV (938~MeV), m_\Delta=1300\errr{100}{100}~MeV (1232~MeV) and m_\Omega=1650\err{70}{50}~MeV (1672~MeV). Direct comparison with experiment for decay constants is obscured by uncertainty in current renormalisations. However, for ratios of decay constants we obtain f_K/f_\pi=1.20\er{3}{2} (1.22) and f_\phi/f_\rho=1.13\er{2}{3} (1.22).Comment: 27 pages, LaTeX, epsf, 11 figs (appended as 21 postscript files, uuencoded), to appear in Phys Rev D, Edinburgh Preprint: 93/524, Southampton Preprint SHEP 92/93-1

The mass of the charm quark from unquenched lattice QCD at fixed lattice spacing

We determine the mass of the charm quark ($m_c$) from lattice QCD with two flavors of dynamical quarks with a mass around the strange quark. We compare this to a determination in quenched QCD which has the same lattice spacing (0.1 fm). We investigate different formulations of the quark mass, based on the Vector Ward Identity, PCAC relation and the FNAL heavy quark formalism. Based on these preliminary results we find no effects due to sea quarks with a mass around strange.Comment: Presented at 21st International Symposium on Lattice Field Theory (LATTICE 2003), Tsukuba, Japan, 15-19 July, 200

The strangeness content of the nucleon

We evaluate the matrix element of $\bar{q} q$ in hadron states on a lattice. We find substantial mixing of the connected and disconnected contributions so that the lattice result that the disconnected contribution to the nucleon is large does not imply that the $\bar{s} s$ content is large. This has implications for dark matter searches.Comment: contribution to Lattice2001(matrixelement

Feasibility study of using the overlap-Dirac operator for hadron spectroscopy

We investigate a number of algorithms that calculate the quark propagators for the overlap-Dirac fermion operator. The QCD simulations were performed at beta = 5.9 with a lattice volume of 16**3*32.Comment: LATTICE99(Chiral Fermions) 3 pages, 2 figures. A problem with the incorrect definition of the overlap mass has been corrected. The results have changed, but not the conclusions of the pape