Improved chiral properties of FLIC fermions

The chiral properties of the fat-link irrelevant clover (FLIC) fermion action are examined. The improved chiral properties of fermion actions incorporating smoothed links are realized in the FLIC action where only the irrelevant operators of the fermion action are constructed with smoothed links. In particular, the histogram of the additive mass renormalization encountered in chiral-symmetry breaking Wilson-type fermion actions is seen to narrow upon introducing fat-links in the irrelevant operators. The exceptional configuration problem of quenched QCD is reduced, enabling access to the light quark mass regime of m_#pi#/m_#rho# #propor to# 0.35. In particular, quenched chiral non-analytic behavior is revealed in the light quark mass dependence of the #DELTA#-baryon mass. FLIC fermions offer a promising approach to revealing the properties of full QCD at light quark masses. (orig.)Available from TIB Hannover: RA 8919(2004-074) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Quark propagator in Landau gauge

The Landau gauge quark propagator in momentum space is investigated using the O(a)-improved Sheikholeslami-Wohlert (SW) quark action with a tree-level mean-field improved coefficient c_s_w. We have studied the unimproved definition of the quark propagator, as well as two different tree-level O(a)-improved propagators. The ultraviolet behavior of the free lattice propagator is studied for each of these in order to establish which of them provides the most reliable description of the quark propagator up to the medium momentum regime. A general method of tree-level correction is introduced. This exploits asymptotic freedom and removes much of the trivial lattice artifacts at medium to high momenta. We obtain results for the quark propagator which are qualitatively similar to those typically used in quark models. A simple extrapolation of the infrared quark mass M(p"2 = 0) to the chiral limit gives 298 #+-# 8 MeV, which is consistent with phenomenological expectations. (orig.)17 refs.Available from TIB Hannover: RA 2999(00-099) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Hybrid meson spectrum from the FLIC action

The spectral properties of hybrid meson interpolating fields are investigated. The quantum numbers of the meson are carried by smeared-source fermion operators and highly-improved chromo-electric and -magnetic field operators composed with APE-smeared links. The effective masses of standard and hybrid operators indicate that the ground state meson is effectively isolated using both standard and hybrid interpolating fields. Focus is placed on interpolating fields in which the large spinor components of the quark and antiquark fields are merged. In particular, the effective mass of the exotic 1"-"+ meson is reported. Further, we report some values for excited mesonic states using a variational process. (orig.)Available from TIB Hannover: RA 2999(03-207) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Electromagnetic form factors wih FLIC fermions

The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative #sigma#(a) improvement and allows efficient access to the light quark-mass regime. FLIC fermions enable the construction of the nonperturbatively #sigma#(a)-improved conserved vector current without the difficulties associated with the fine tuning of the improvement coefficients. The simulations are performed with an #sigma#(a"2) mean-field improved plaquette-plus-rectangle gluon action on a 20"3 x 40 lattice with a lattice spacing of 0.128 fm, enabling the first simulation of baryon form factors at light quark masses on a large volume lattice. Magnetic moments, electric charge radii and magnetic radii are extracted from these form factors, and show interesting chiral nonanalytic behavior in the light quark mass regime. (orig.)Available from TIB Hannover: RA 2999(03-210) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The strangeness magnetic moment of the nucleon from FLIC fermions

By imposing the constraints of charge symmetry we show that the strangeness magnetic moment of the nucleon can be expressed in terms of empirical magnetic moments and ratios of valence quark magnetic moments. The latter are determined using modern chiral extrapolation techniques and recent low mass lattice QCD simulations of the individual quark contributions to the magnetic moments of the nucleon octet. The result is a precise determination of G_M"s, namely -0.043 #+-# 0.013 #mu#N, which is consistent with the latest experimental measurements. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-211) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Systematic uncertainties in the precise determination of the strangeness magnetic moment of the nucleon

Systematic uncertainties in the recent precise determination of the strangeness magnetic moment of the nucleon are identified and quantified. In summary, G_M"s=-0.046 #+-# 0.019 #mu#_N. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(05-014) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Scaling of FLIC fermions

Hadron masses are calculated in quenched lattice QCD on a variety of lattices in order to probe the scaling behavior of the Fat-Link Irrelevant Clover (FLIC) fermion action, a fat-link clover fermion action in which the purely irrelevant operators of the fermion action are constructed using APE-smeared links. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative O(a) improvement where near-continuum results are obtained at finite lattice spacing. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(04-073) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Electromagnetic form factors with FLIC fermions

The fat-link irrelevant clover (FLIC) fermion action provides a new form of nonperturbative O(a) improvement and allows efficient access to the light quark-mass regime. FLIC fermions enable the construction of the nonperturbatively O(a)-improved conserved vector current without the difficulties associated with the fine tuning of the improvement coefficients. The simulations are performed with an O(a"2) mean-field improved plaquette-plus-rectangle gluon action on a 20"3 x 40 lattice with a lattice spacing of 0.128 fm, enabling the first simulation of baryon form factors at light quark masses on a large volume lattice. Magnetic moments, electric charge radii and magnetic radii are extracted from these form factors, and show interesting chiral nonanalytic behavior in the light quark mass regime. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-157) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Hybrid mesons on the lattice with FLIC fermions

The spectral properties of hybrid meson interpolating fields are investigated. The quantum numbers of the meson are carried by smeared-source fermion operators and highly-improved chromo-electric and -magnetic field operators composed with APE-smeared links. The effective masses of standard and hybrid operators indicate that the ground state meson is effectively isolated using both standard and hybrid interpolating fields. Focus is placed on interpolating fields in which the large spinor components of the quark and antiquark fields are merged. In particular, the effective mass of the exotic 1"-"+ meson is reported. Further, we report some values for excited mesonic states using a variational process. (orig.)Available from TIB Hannover: RA 2999(03-208) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Excitation and ionization cross-sections for He I excited states (n=2/4, #DELTA#S=0). Pt. 1 Born and K-matrix approaches

There are two types of methods for calculation of excitation and ionization of atoms and ions by electrons. A. Sophisticated close coupling (CC) - type methods, such as R - matrix and CCC (converging close coupling). They usually provide sufficiently accurate results. However there are some disagreements and questions in particular cases. B. Rather simple Born - type (I order) methods with possible inclusion of exchange and normalization (B). For ions Coulomb field is also included (CB - Coulomb-Born). Generally cross sections obtained by A-methods are preferable, but they are available for very limited number of transitions and atoms. Fast calculations of many transitions required for atomic base in diagnostic code are in fact unreliable. Therefore usage of the B-methods is necessary. Unfortunately the accuracy of calculations by simple B methods is often insufficient. To create the real data bases it is important to understand a physical reason of errors and to develope sufficiently simple ways of correction. One very efficient way is the method of K-matrix. It is based on I order B calculation of matrix K for a given set of transitions. Then S-matrix and cross section #sigma# are calculated. The B-methods and full K-matrix approach are realized in the coupled programs ATOM-AKM. They can be run on PC-486 or higher and require about 10 minutes for 10 channels (transitions) in 10-20 energy points. In this paper we present results of calculations of excitation and ionization cross-sections from He I excited states (nl - n'l' for n, n' = 2 / 4 without change of spin). Different methods are used and compared. We use atomic units with Ry = 13.60 eV for energy and #pi#a_0"2 for cross sections. (orig.)10 refs.SIGLEAvailable from TIB Hannover: RA 831(3479) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman