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[en] We show that given one Cl(a) improvement constant, bm, all the remaining quantities needed to define the renormalized and O(a) improved dimension-3 quark bilinears can be obtained by studying the matrix elements of these operators between external quark states in a fixed gauge.

[en] The relativistic five-quark equations are found in the framework of the dispersion relation technique. The five-quark amplitude for the N*(1688) resonance including u- and d-quarks is calculated. The pole of this amplitude determines the mass of nonstrange pentaquark M=1686 MeV and the width about 7 MeV. The results are in good agreement with the evidence for a narrow N*(1688) resonance. (author)

[en] We show how to improve the molecular dynamics step of Hybrid Monte Carlo, both by tuning the integrator using Poisson brackets measurements and by the use of force gradient integrators. We present results for moderate lattice sizes. We have presented a novel way of tuning an integrator, together with a practical example using a moderate lattice size. This tuning procedure can be used for all lattice gauge and fermionic actions. We are working towards a general implementation of the calculation of Poisson brackets and force gradient terms in Chroma. In the near future we will consider the tuning of HMC simulations on larger lattices and smaller quark masses, and we will also consider other widely used lattice actions.

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[en] We have devised and demonstrated the successful operation of a low-cost, high-mass throughput technique capable of performing bulk matter searches for fractionally charged particles based on an improved Millikan liquid drop method. The method uses a stroboscopic lamp and a charge coupled device video camera to image the trajectories of silicone oil drops falling through air in the presence of a vertical, alternating electric field. The images of the trajectories are computer processed in real time, the electric charge on a drop being measured with an rms error of 0.025 of an electron charge. This error is dominated by Brownian motion. In the first use of this method, we have looked at 5974941 drops and found no evidence for fractional charges in 1.07 mg of oil. With 95% confidence, the concentration of isolated quarks with ±1/3e or ±2/3e in silicone oil is less than one per 2.14x10²⁰ nucleons. copyright 1996 The American Physical Society