The Paraldor Project

Paraldor is an experiment in bringing the power of categorical languages to lattice QCD computations. Our target language is Aldor, which allows the capture of the mathematical structure of physics directly in the structure of the code using the concepts of categories, domains and their inter-relationships in a way which is not otherwise possible with current popular languages such as Fortran, C, C++ or Java. By writing high level physics code portably in Aldor, and implementing switchable machine dependent high performance back-ends in C or assembler, we gain all the power of categorical languages such as modularity, portability, readability and efficiency.Comment: 4 pages, 2 figures, Lattice 2002 conference proceeding

Possible resonance free lattices for the VLHC

A systematic search for resonance-free lattices has been performed. Numerous solutions exist for sets of about fifty cells. A VLHC-like machine could be made of blocks of 61 cells which are free from resonances up to tenth order. A tracking test shows a 20% improvement of the dynamic aperture with respect to standard cells, for several multi-pole components. It opens the possibility of relaxing the constraints on systematic multipole components for the cells. The tolerances on field quality will then be by chromatic and an-harmonic effects of the mul-tipole components

A lattice determination of moments of unpolarised nucleon structure functions using improved Wilson fermions

Within the framework of quenched lattice QCD and using O(a) improved Wilson fermions and non-perturbative renormalisation, a high statistics computation of low moments of the unpolarised nucleon structure functions is given. Particular attention is paid to the chiral and continuum extrapolations.Comment: LaTeX, 66 pages, 22 figure

Stress and Buckling of Internally Pressurized, Elastic-Plastic Torispherical Vessel leads- Comparisons of Test and Theory

Several aluminum and mild steel torispJxerical lieads were tested by Galletly and b

Substance misuse in patients with acute mental illness

The document attached has been archived with permission from the editor of the Medical Journal of Australia. An external link to the publisher’s copy is included.Cherrie Ann Galletly, Darryl P Watso

Structure functions and form factors close to the chiral limit from lattice QCD

Results for nucleon matrix elements (arising from moments of structure functions) and form factors from a mixture of runs using Wilson, clover and overlap fermions (both quenched and unquenched) are presented and compared in an effort to explore the size of the chiral `regime', lattice spacing errors and quenching artefacts. While no run covers this whole range of effects the partial results indicate a picture of small lattice spacing errors, small quenching effects and only reaching the chiral regime at rather light quark masses.Comment: 7 pages, 7 figures; contribution to the 2003 Workshop on Lattice Hadron Physics, Cairns, Australia; error in Fig. 4 corrected; minor text change

Topological Structure of the QCD Vacuum Revealed by Overlap Fermions

Overlap fermions preserve a remnant of chiral symmetry on the lattice. They are a powerful tool to investigate the topological structure of the vacuum of Yang-Mills theory and full QCD. Recent results concerning the localization of topological charge and the localization and local chirality of the overlap eigenmodes are reported. The charge distribution is radically different, if a spectral cut-off for the Dirac eigenmodes is applied. The density q(x) is changing from the scale-a charge density (with full lattice resolution) to the ultraviolet filtered charge density. The scale-a density, computed on the Linux cluster of LRZ, has a singular, sign-coherent global structure of co-dimension 1 first described by the Kentucky group. We stress, however, the cluster properties of the UV filtered topological density resembling the instanton picture. The spectral cut-off can be mapped to a bosonic smearing procedure. The UV filtered field strength reveals a high degree of (anti)selfduality at "hot spots" of the action. The fermionic eigenmodes show a high degree of local chirality. The lowest modes are seen to be localized in low-dimensional space-time regions.Comment: 13 pages, 11 figures, accepted to appear in the Proceedings of "HLRB, KONWIHR and Linux-Cluster: Review, Results and Future Projects Workshop", Leibniz Rechenzentrum Munich, December 200

On the Isomorphic Description of Chiral Symmetry Breaking by Non-Unitary Lie Groups

It is well-known that chiral symmetry breaking ($\chi$SB) in QCD with $N_{f}=2$ light quark flavours can be described by orthogonal groups as $O(4) \to O(3)$, due to local isomorphisms. Here we discuss the question how specific this property is. We consider generalised forms of $\chi$SB involving an arbitrary number of light flavours of continuum or lattice fermions, in various representations. We search systematically for isomorphic descriptions by non-unitary, compact Lie groups. It turns out that there are a few alternative options in terms of orthogonal groups, while we did not find any description entirely based on symplectic or exceptional Lie groups. If we adapt such an alternative as the symmetry breaking pattern for a generalised Higgs mechanism, we may consider a Higgs particle composed of bound fermions and trace back the mass generation to $\chi$SB. In fact, some of the patterns that we encounter appear in technicolour models. In particular if one observes a Higgs mechanism that can be expressed in terms of orthogonal groups, we specify in which cases it could also represent some kind of $\chi$SB of techniquarks.Comment: 18 pages, to appear in Int. J. Mod. Phys.

Hadron spectrum, quark masses and decay constants from light overlap fermions on large lattices

We present results from a simulation of quenched overlap fermions with L\"uscher-Weisz gauge field action on lattices up to $24^3 48$ and for pion masses down to $\approx 250$ MeV. Among the quantities we study are the pion, rho and nucleon masses, the light and strange quark masses, and the pion decay constant. The renormalization of the scalar and axial vector currents is done nonperturbatively in the $RI-MOM$ scheme. The simulations are performed at two different lattice spacings, $a \approx 0.1$ fm and $\approx 0.15$ fm, and on two different physical volumes, to test the scaling properties of our action and to study finite volume effects. We compare our results with the predictions of chiral perturbation theory and compute several of its low-energy constants. The pion mass is computed in sectors of fixed topology as well