Is the chiral U(1) theory trivial?

The chiral U(1) theory differs from the corresponding vector theory by an imaginary contribution to the effective action which amounts to a phase factor in the partition function. The vector theory, i.e. QED, is known to be trivial in the continuum limit. It is argued that the presence of the phase factor will not alter this result and the chiral theory is non-interacting as well. (orig.)SIGLEAvailable from TIB Hannover: RR 2999(00-161) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Higher-twist corrections to nucleon structure functions from lattice QCD

A genuinely non-perturbative evaluation of higher-twist contributions to the structure functions of the nucleon, with all mixing effects and renormalon ambiguities taken care of, is presented. Higher-twist corrections turn out to be significant at moderate values of q"2. (orig.)6 refs.Available from TIB Hannover: RA 2999(99-069) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Lattice HQET with exponentially improved statistical precision

We modify the Eichten-Hill action of static quarks on the lattice in order to achieve a reduction of statistical errors but retaining the O(a)-improvement properties of that action. Statistical fluctuations are reduced by a factor which grows exponentially with Euclidean time, x_0. For the first time, B-meson correlation functions are computed with good statistical precision in the static approximation for x_0 >1 fm. At lattice spacings a#approx#0.1 fm, a#approx#0.08 fm and a#approx#0.07 fm the B_s-meson decay constant is determined in static and quenched approximations. A correction due to the finite mass of the b-quark is estimated by combining these static results with a recent determination of F_D__s (orig.)SIGLEAvailable from TIB Hannover: RA 2999(03-087) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Baryonic flux in quenched and two-flavor dynamical QCD

We study the distribution of color electric flux of the three-quark system in quenched and full QCD (with N_f=2 flavors of dynamical quarks) at zero and finite temperature. To reduce ultra-violet fluctuations, the calculations are done in the Abelian projected theory fixed to the maximally Abelian gauge. In the confined phase we find clear evidence for a Y-shape flux tube surrounded and formed by the solenoidal monopole current, in accordance with the dual superconductor picture of confinement. In the deconfined, high temperature phase monopoles cease to condense, and the distribution of the color electric field becomes Coulomb-like. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(04-004) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Profiles of the broken string in two-flavor QCD below and above the finite temperature transition

We study the Abelian flux tube profile of mesonic and the baryonic configurations of static quarks below and above the finite-temperature transition in N_f = 2 full QCD. To reduce effects of ultra-violet fluctuations we measure Abelian distributions of the action density, the color-electric field and the monopole current after fixing to the maximally Abelian gauge. Changing the distance R between quarks for fixed T/T_c < 1, one can see a clear signal of string breaking for large R. The electric field becomes Coulomb-like and the circulating monopole current disappears. We study also the temperature dependence of the flux profile for fixed R #approx# 0.7 fm. The disappearance of the squeezed flux is observed clearly above T_c. Similar behaviors are observed both in the mesonic and the baryonic systems. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(04-005) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Structure of the baryonic flux tube in N_f=2 lattice QCD at finite temperature

We study the flux tube profile in the baryonic system in full QCD at finite temperature of N_t=8 lattice. We fix the maximally Abelian gauge and measure the monopole and the photon parts of the Abelian action density, the color electric field and the monopole current on both sides of the finite temperature transition. We demonstrate the disappearance of the flux tube in the high temperature phase. (orig.)Available from TIB Hannover: RA 2999(03-144) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman