Strange quarks and lattice QCD

The last few years have seen a dramatic improvement in our knowledge of the strange form factors of the nucleon. With regard to the vector from factors the level of agreement between theory and experiment gives us considerable confidence in our ability to calculate with non-perturbative QCD. The calculation of the strange scalar form factor has moved significantly in the last two years, with the application of new techniques which yield values considerably smaller than believed for the past 20 years. These new values turn out to have important consequences for the detection of neutralinos, a favourite dark matter candidate. Finally, very recent lattice studies have resurrected interest in the famed H-dibaryon, with modern chiral extrapolation of lattice data suggesting that it may be only slightly unbound. We review some of the major sources of uncertainty in that chiral extrapolation.Comment: Invited talk at the Asia-Pacific few Body Conference, Seoul Kore

Infrared Behavior of the Gluon Propagator on a Large Volume Lattice

The first calculation of the gluon propagator using an order a^2 improved action with the corresponding order a^2 improved Landau gauge fixing condition is presented. The gluon propagator obtained from the improved action and improved Landau gauge condition is compared with earlier unimproved results on similar physical lattice volumes of 3.2^3 \times 6.4 fm^4. We find agreement between the improved propagator calculated on a coarse lattice with lattice spacing a = 0.35 fm and the unimproved propagator calculated on a fine lattice with spacing a = 0.10 fm. This motivates us to calculate the gluon propagator on a coarse large-volume lattice 5.6^3 \times 11.2 fm^4. The infrared behavior of previous studies is confirmed in this work. The gluon propagator is enhanced at intermediate momenta and suppressed at infrared momenta. Therefore the observed infrared suppression of the Landau gauge gluon propagator is not a finite volume effect.Comment: 8 pages, 4 figures, minor typos corrected and repsonse to referees comment

Gluon Propagator on Coarse Lattices in Laplacian Gauges

The Laplacian gauge is a nonperturbative gauge fixing that reduces to Landau gauge in the asymptotic limit. Like Landau gauge, it respects Lorentz invariance, but it is free of Gribov copies; the gauge fixing is unambiguous. In this paper we study the infrared behavior of the lattice gluon propagator in Laplacian gauge by using a variety of lattices with spacings from $a = 0.125$ to 0.35 fm, to explore finite volume and discretization effects. Three different implementations of the Laplacian gauge are defined and compared. The Laplacian gauge propagator has already been claimed to be insensitive to finite volume effects and this is tested on lattices with large volumes.Comment: RevTex 4.0, 14 pages, 9 colour figures; Correction to Reference

Scaling behavior of the overlap quark propagator in Landau gauge

The properties of the momentum space quark propagator in Landau gauge are examined for the overlap quark action in quenched lattice QCD. Numerical calculations are done on three lattices with different lattice spacings and similar physical volumes to explore the approach of the quark propagator toward the continuum limit. We have calculated the nonperturbative momentum-dependent wave function renormalization function Z(p) and the nonperturbative mass function M(p) for a variety of bare quark masses and perform an extrapolation to the chiral limit. We find the behavior of Z(p) and M(p) are in reasonable agreement between the two finer lattices in the chiral limit, however the data suggest that an even finer lattice is desirable. The large momentum behavior is examined to determine the quark condensate.Comment: 9 pages, 5 figures, Revtex 4. Streamlined presentation, additional data. Final versio

Calibration of Smearing and Cooling Algorithms in SU(3)-Color Gauge Theory

The action and topological charge are used to determine the relative rates of standard cooling and smearing algorithms in pure SU(3)-color gauge theory. We consider representative gauge field configurations on $16^3\times 32$ lattices at $\beta=5.70$ and $24^3\times 36$ lattices at $\beta=6.00$. We find the relative rate of variation in the action and topological charge under various algorithms may be succinctly described in terms of simple formulae. The results are in accord with recent suggestions from fat-link perturbation theory.Comment: RevTeX, 25 pages, 22 figures, full resolution jpeg version of Fig. 22 can be obtained from http://www.physics.adelaide.edu.au/cssm/papers_etc/SmearingComp.jp

Deuteron Electroweak Disintegration

We study the deuteron electrodisintegration with inclusion of the neutral currents focusing on the helicity asymmetry of the exclusive cross section in coplanar geometry. We stress that a measurement of this asymmetry in the quasi elastic region is of interest for an experimental determination of the weak form factors of the nucleon, allowing one to obtain the parity violating electron neutron asymmetry. Numerically, we consider the reaction at low momentum transfer and discuss the sensitivity of the helicity asymmetry to the strangeness radius and magnetic moment. The problems coming from the finite angular acceptance of the spectrometers are also considered.Comment: 30 pages, Latex, 7 eps figures, submitted to Phys.Rev.C e-mail: [email protected] , [email protected]

The discontinuous nature of chromospheric activity evolution

Chromospheric activity has been thought to decay smoothly with time and, hence, to be a viable age indicator. Measurements in solar type stars in open clusters seem to point to a different conclusion: chromospheric activity undergoes a fast transition from Hyades level to that of the Sun after about 1 Gyr of main--sequence lifetime and any decaying trend before or after this transition must be much less significant than the short term variations.Comment: 6 pages, 1 figure, to be published in Astrophysics and Space Scienc

The Proton Spin and Flavor Structure in the Chiral Quark Model

After a pedagogical review of the simple constituent quark model and deep inelastic sum rules, we describe how a quark sea as produced by the emission of internal Goldstone bosons by the valence quarks can account for the observed features of proton spin and flavor structures. Some issues concerning the strange quark content of the nucleon are also discussed.Comment: 59 pages with table of contents, Lecture delivered at the Schladming Winter School (March 1997), to be published by Springer-Verlag under the title "Computing Particle Properties" (eds. C. B. Lang and H. Gausterer

GH safety workshop position paper: A critical appraisal of recombinant human GH therapy in children and adults

Recombinant human GH (rhGH) has been in use for 30 years, and over that time its safety and efficacy in children and adults has been subject to considerable scrutiny. In 2001, a statement from the GH Research Society (GRS) concluded that 'for approved indications, GH is safe'; however, the statement highlighted a number of areas for on-going surveillance of long-Term safety, including cancer risk, impact on glucose homeostasis, and use of high dose pharmacological rhGH treatment. Over the intervening years, there have been a number of publications addressing the safety of rhGH with regard to mortality, cancer and cardiovascular risk, and the need for long-Term surveillance of the increasing number of adults who were treated with rhGH in childhood. Against this backdrop of interest in safety, the European Society of Paediatric Endocrinology (ESPE), the GRS, and the Pediatric Endocrine Society (PES) convened a meeting to reappraise the safety of rhGH. The ouput of the meeting is a concise position statement