A lattice calculation of the pion form factor with Ginsparg-Wilson-type fermions

Results for Monte Carlo calculations of the electromagnetic vector and scalar form factors of the pion in a quenched simulation are presented. We work with two different lattice volumes up to a spatial size of 2.4 fm at a lattice spacing of 0.148 fm. The pion form factors in the space-like region are determined for pion masses down to 340 MeV.Comment: REVTeX 4, 8 pages, 9 figures, 4 tables; final versio

Large pion pole in Z_{S}^{MOM}/Z_{P}^{MOM} from Wilson action data

We show that, contrarily to recent claims, data from the Wilson (unimproved) fermionic action at three different beta values demonstrate the presence of a large Goldstone boson contribution in the quark pseudoscalar vertex, quantitatively close to our previous estimate based on the SW action with c_{SW}=1.769. We show that discretisation errors on Z_{S}^{MOM}/Z_{P}^{MOM} seem to be much smaller than the Goldstone pole contribution over a very large range of momenta. The subtraction of this non perturbative contribution leads to numbers close to one-loop BPT.Comment: 12 pages, 5 figures, laTeX, minor corrections of typos, beta dependence made more explicit, added one table giving the contribution of the Goldstone vs. the discretisation errors at ap=

B_K from quenched overlap QCD

We present an exploratory calculation of the standard model Delta S=2 matrix element relevant for indirect CP violation in K -> pi pi decays. The computation is performed with overlap fermions in the quenched approximation at beta=6.0 on a 16^3x32 lattice. The resulting bare matrix element is renormalized non-perturbatively. Our preliminary result is B_K^{NDR}(2 GeV)=0.61(7), where the error does not yet include an estimate of systematic uncertainties.Comment: 3 pages, 2 figures, Lattice2002(matrixel). Parallel session talk by L. Lellouch at the 20th International Symposium on Lattice Field Theory (Lattice 2002), Boston, Massachusetts, 24-29 June 200

3-point functions from twisted mass lattice QCD at small quark masses

We show at the example of the matrix element between pion states of a twist-2, non-singlet operator that Wilson twisted mass fermions allow to compute this phenomenologically relevant quantitiy at small pseudo scalar masses of O(270 MeV). In the quenched approximation, we investigate the scaling behaviour of this observable that is derived from a 3-point function by applying two definitions of the critical mass and find a scaling compatible with the expected O(a^2) behaviour in both cases. A combined continuum extrapolations allows to obtain reliable results at small pion masses, which previously could not be explored by lattice QCD simulations.Comment: 6 pages, 2 figures, talk presented at Lattice 200

Power Corrections to Perturbative QCD and OPE in Gluon Green Functions

We show that QCD Green functions in Landau Gauge exhibit sizable $O(1/\mu^2)$ corrections to the expected perturbative behavior at energies as high as 10 GeV. We argue that these are due to a $$-condensate which does not vanish in Landau gauge.Comment: 3 pages 1 figure lattice2001 (gaugetheories

THERIA_G: a software program to numerically model prograde garnet growth

We present the software program THERIA_G, which allows for numerical simulation of garnet growth in a given volume of rock along any pressure-temperature-time (P-T-t) path. THERIA_G assumes thermodynamic equilibrium between the garnet rim and the rock matrix during growth and accounts for component fractionation associated with garnet formation as well as for intracrystalline diffusion within garnet. In addition, THERIA_G keeps track of changes in the equilibrium phase relations, which occur during garnet growth along the specified P-T-t trajectory. This is accomplished by the combination of two major modules: a Gibbs free energy minimization routine is used to calculate equilibrium phase relations including the volume and composition of successive garnet growth increments as P and T and the effective bulk rock composition change. With the second module intragranular multi-component diffusion is modelled for spherical garnet geometry. THERIA_G allows to simulate the formation of an entire garnet population, the nucleation and growth history of which is specified via the garnet crystal size frequency distribution. Garnet growth simulations with THERIA_G produce compositional profiles for the garnet porphyroblasts of each size class of a population and full information on equilibrium phase assemblages for any point along the specified P-T-t trajectory. The results of garnet growth simulation can be used to infer the P-T-t path of metamorphism from the chemical zoning of garnet porphyroblasts. With a hypothetical example of garnet growth in a pelitic rock we demonstrate that it is essential for the interpretation of the chemical zoning of garnet to account for the combined effects of the thermodynamic conditions of garnet growth, the nucleation history and intracrystalline diffusio

Gluon propagator, triple gluon vertex and the QCD coupling constant

We study the UV-scaling of the flavorless gluon propagator in the Landau gauge in an energy window up to 9 GeV. Dominant hypercubic lattice artifacts are eliminated. A large set of renormalization schemes is used to test asymptotic scaling. We compare with our results obtained directly from the triple gluon vertex. We end-up with \Lambda_{\bar{\rm{MS}}} = 318(12)(5) MeV and 292(5)(15) MeV respectively for these two methods, compatible which each other but significantly above the Schrodinger method estimate.Comment: 3 pages, LaTeX with two figures; presented at LATTICE9

A Quaternary Solution Model for White Micas Based on Natural Coexisting Phengite-Paragonite Pairs

A thermodynamic model for the quaternary white mica solid solution with end-members muscovite-Mg-celadonite-paragonite-Fe-celadonite (Ms-MgCel-Pg-FeCel) is presented. The interaction energies for the MgCel-Pg join, the FeCel-Pg join and the ternary interactions were obtained from natural coexisting phengite-paragonite pairs. Phengite-paragonite pairs were selected based on the criteria that their chemical compositions may be represented as a linear combination of the model end-member compositions and that the respective formation conditions (350-650°C, 4-21 kbar) are accurately known. Previously published excess free energy expressions were used for the Ms-Pg, Ms-MgCel and Ms-FeCel binaries. The suggested mixing model was tested by calculating multicomponent equilibrium phase diagrams. This proved to be particularly well suited to reproduce compositional variations of white micas from amphibolite-facies metapelite