Quark mass dependence of the pseudoscalar hairpin vertex

In a recent investigation of chiral behavior in quenched lattice QCD, the flavor-singlet pseudoscalar ``hairpin'' vertex associated with the eta prime mass was studied for pion masses ranging from approximately 275 to 675 MeV. Throughout this mass range, the quark-disconnected pseudoscalar correlator is well-described by a pure double-pion-pole diagram with a p^2 independent mass insertion. The residue of the double pole was found to exhibit a significant quark mass dependence, evidenced by a negative slope of the effective mass insertion (m_0^{eff})^2 as a function of m_{\pi}^2. It has been observed by Sharpe that, with a consistent NLO calculation in quenched chiral perturbation theory, this mass dependence is uniquely predicted in terms of the single-pole coefficient \alpha_{\Phi} and the Leutwyler parameter L_5. Since \alpha_{\Phi} is found to be approximately zero, the chiral slope of the double-pole residue determines a value for L_5. This provides a consistency check between the chiral slope of the hairpin mass insertion and that of the pion decay constant. We investigate the consistency of these mass dependences in our Monte Carlo results at two values of lattice spacing. Within statistics, the slopes are found to be consistent with the Q\chiPT prediction, confirming that the observed negative slope of m_0^{eff} arises as an effect of the L_5 Leutwyler term.Comment: 4 pages, 1 figure, LaTe

QED2 as a testbed for interpolations between quenched and full QCD

Lattice QED2 with the Wilson formulation of fermions is used as a convenient model system to study artifacts of the quenched approximation on a finite lattice. The quenched functional integral is shown to be ill-defined in this system as a consequence of the appearance of exactly real modes for physical values of the fermion mass. The location and frequency of such modes is studied as a function of lattice spacing, lattice volume, topological charge and improved action parameters. The efficacy of the recently proposed modified quenched approximation is examined, as well as a new approach to the interpolation from the quenched to full dynamical theory employing a truncated form of the fermion determinant.Comment: Talk presented by A. Duncan at LATTICE97 (theoretical developments

Perspectives for heavy flavour production in ATLAS

The prospects of making charm and bottom production measurements with the ATLAS experiment are presented

Physical Effects of Infrared Quark Eigenmodes in LQCD

A truncated determinant algorithm is used to study the physical effects of the quark eigenmodes associated with eigenvalues below 400 MeV. This initial study focuses on coarse lattices (with O(a^2) improved gauge action), light internal quark masses and large physical volumes. Four bellwether full QCD processes are discussed: topological charge distributions, the eta prime propagator, string breaking as observed in the static energy and the rho decay into two pions.Comment: LATTICE99(Confinement); 3pgs(Latex), 4figs.(eps

Interpretation and Legal Theory, Andrei Marmor

Book review of Interpretation and Legal Theory by Andrei Marmor and published by Clarendon Press (Oxford), 1992. (193 pp.