Chris Michael

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Lattice QCD determinations appropriate to hadron spectroscopy are reviewed with emphasis on the glueball and hybrid meson states in the quenched approximation. Hybrids are discussed for heavy and for light quarks. The effects of sea quarks (unquenching) are explored. Heavy-light systems are presented particularly excited B mesons.
We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf = 2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of(More)
Recent theoretical models suggest that perceived racism acts as a stressor for African Americans and may be associated with a variety of negative psychological consequences, notably paranoia. Paranoia among African Americans is believed to reflect the lower end of the paranoia continuum based on experiences with racism. Thus, it may be beneficial to measure(More)
We discuss lattice methods to obtain the derivatives of a lattice meson mass with respect to the bare sea and valence quark masses. Applications are made to quenched and dynamical fermion configurations. We find evidence for significant differences between quenched and dynamical fermion configurations. We discuss how to relate dependence on the bare lattice(More)
We study a new method – maximal variance reduction – for reducing the variance of stochastic estimators for quark propagators. We find that while this method is comparable to usual iterative inversion for light-light mesons, a considerable improvement is achieved for systems containing at least one infinitely heavy quark. Such systems are needed for heavy(More)
We explore the transitions B(0) to B π and Bs(0 ) to B K from lattice QCD withNf = 2 flavours of sea quark, using the static approximation for the heavy quark. We evaluate the effective coupling constants, predicting a B(0) to B π width of around 160 MeV. Our result for the coupling strength adds to the evidence that the Bs(0 ) meson is not predominantly a(More)
In a recent paper [1] we presented precise lattice QCD results of our European Twisted Mass Collaboration (ETMC). They were obtained by employing two mass-degenerate flavours of twisted mass fermions at maximal twist. In the present paper we give details on our simulations and the computation of physical observables. In particular, we discuss the problem of(More)
We explore the decay of a vector meson to two pseudoscalar mesons on the lattice with Nf = 2 flavours of sea quark. Although we are working with quark masses that do not allow a physical decay, we show how the transition rate can be evaluated from the amplitude for ρ→ ππ and from the annihilation component of ππ → ππ. We explore the decay amplitude for two(More)
We present a study of the SU(3) glueball spectrum for all J values at lattice spacings down to a = 3.73(6) GeV (β = 6.4) using lattices of size up to 32. We extend previous studies and show that the continuum limit has effectively been reached. The number of clearly identified J states has been substantially increased. There are no clear signals for(More)