Generalised parton distributions of the pion in partially-quenched chiral perturbation theory

We consider the pion matrix elements of the isoscalar and isovector combinations of the vector and tensor twist-two operators that determine the moments of the various pion generalised parton distributions. Our analysis is performed using partially-quenched chiral perturbation theory. We work in the SU(2) and SU(4|2) theories and present our results at infinite volume and also at finite volume where some subtleties arise. These results are useful for extrapolations of lattice calculations of these matrix elements at small momentum transfer to the physical regime.Comment: 15 page

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

Extreme-scaling Applications 24/7 on JUQUEEN Blue Gene/Q

Jülich Supercomputing Centre has offered Extreme Scaling Workshops since 2009, with the latest edition in February 2015 giving seven international code teams an opportunity to (im)prove the scaling of their applications to all 458752 cores of the JUQUEEN IBM BlueGene/Q. Each of them successfully adapted their application codes and datasets to the restricted compute-node memory and exploit the massive parallelism with up to 1.8 million processes or threads. They thereby qualified to become members of the High-Q Club which now has over 24 codes demonstrating extreme scalability. Achievements in both strong and weak scaling are compared, and complemented with a review of program languages and parallelisation paradigms, exploitation of hardware threads, and file I/O requirements

Chiral symmetry and the axial nucleon to Delta(1232) transition form factors

We study the momentum and the quark mass dependence of the axial nucleon to Delta(1232) transition form factors in the framework of non-relativistic chiral effective field theory to leading-one-loop order. The outcome of our analysis provides a theoretical guidance for chiral extrapolations of lattice QCD results with dynamical fermions.Comment: 18 pages, 3 figure

Baryon operators and spectroscopy in lattice QCD

The construction of the operators and correlators required to determine the excited baryon spectrum is presented, with the aim of exploring the spatial and spin structure of the states while minimizing the number of propagator inversions. The method used to construct operators that transform irreducibly under the symmetries of the lattice is detailed, and the properties of example operators are studied using domain-wall fermion valence propagators computed on MILC asqtad dynamical lattices.Comment: 7 pages, 2 figures, to appear in Proceedings of Workshop on Lattice Hadron Physics 2003, Cairns, Australia, July 22 - July 30, 200

A note on the QCD evolution of generalized form factors

Generalized form factors of hadrons are objects appearing in moments of the generalized parton distributions. Their leading-order DGLAP-ERBL QCD evolution is exceedingly simple and the solution is given in terms of matrix triangular structures of linear equations where the coefficients are the evolution ratios. We point out that this solution has a practical importance in analyses where the generalized form factors are basic objects, e.g., the lattice-gauge studies or models. It also displays general features of their evolution.Comment: 4 page

Domain decomposition improvement of quark propagator estimation

Applying domain decomposition to the lattice Dirac operator and the associated quark propagator, we arrive at expressions which, with the proper insertion of random sources therein, can provide improvement to the estimation of the propagator. Schemes are presented for both open and closed (or loop) propagators. In the end, our technique for improving open contributions is similar to the ``maximal variance reduction'' approach of Michael and Peisa, but contains the advantage, especially for improved actions, of dealing directly with the Dirac operator. Using these improved open propagators for the Chirally Improved operator, we present preliminary results for the static-light meson spectrum. The improvement of closed propagators is modest: on some configurations there are signs of significant noise reduction of disconnected correlators; on others, the improvement amounts to a smoothening of the same correlators.Comment: 19 pages, 8 figures, version to appear in Computer Physics Communication

Extracting excited states from lattice QCD: the Roper resonance

We present a new method for extracting excited states from a single two-point correlation function calculated on the lattice. Our method simply combines the correlation function evaluated at different time slices so as to ``subtract'' the leading exponential decay (ground state) and to give access to the first excited state. The method is applied to a quenched lattice study (volume = 24^3 x 64, beta = 6.2, 1/a = 2.55 GeV) of the first excited state of the nucleon using the local interpolating operator O = [uT C gamma5 d] u. The results are consistent with the identification of our extracted excited state with the Roper resonance N'(1440). The switching of the level ordering with respect to the negative-parity partner of the nucleon, N*(1535), is not seen at the simulated quark masses and, basing on crude extrapolations, is tentatively expected to occur close to the physical point.Comment: version to apper in Phys. Lett. B; additions in the presentation of the method; 3 references added; no change in the results and in the figure

Low-Lying Nucleons from Chirally Improved Fermions

We report on our preliminary results on the low-lying excited nucleon spectra which we obtain through a variational basis formed with three different interpolators.Comment: Contributed to Lattice 2003(spectrum), Tsukub

Excited hadrons from improved interpolating fields

The calculation of quark propagators for Ginsparg-Wilson-type Dirac operators is costly and thus limited to a few different sources. We present a new approach for determining spatially optimized operators for lattice spectroscopy of excited hadrons. Jacobi smeared quark sources with different widths are combined to construct hadron operators with different spatial wave functions. We study the Roper state and excited rho and pion mesons.Comment: Lattice2004(spectrum), 3 pages, 1 figure, (LaTeX style file espcrc2.sty and AMS style files