Improved actions and asymptotic scaling in lattice Yang-Mills theory

Improved actions in SU(2) and SU(3) lattice gauge theories are investigated with an emphasis on asymptotic scaling. A new scheme for tadpole improvement is proposed. The standard but heuristic tadpole improvement emerges from a mean field approximation from the new approach. Scaling is investigated by means of the large distance static quark potential. Both, the generic and the new tadpole scheme yield significant improvements on asymptotic scaling when compared with loop improved actions. A study of the rotational symmetry breaking terms, however, reveals that only the new improvement scheme efficiently eliminates the leading irrelevant term from the action.Comment: minor modifications, improved presentatio

Lambda-parameter of lattice QCD with Symanzik improved gluon actions

We compute the ratio Lambda_L/Lambda_MS, where the scale parameter Lambda_L is associated with a lattice formulation of QCD. We consider a 3-parameter family of gluon actions, which are most frequently used for O(a) improvement a` la Symanzik. The gluon action is put togeter with standard discretizations for fermions (Wilson/clover, overlap), to provide Lambda_L for several possible combinations of fermion and gluon actions. We employ the background field technique in order to calculate the 1PI 2-point function of the background field; this leads to the coupling constant renormalization function, Z_g, at 1-loop level. Our results are obtained for an extensive range of values for the Symanzik coefficients.Comment: 11 pages, 3 figures, 3 table

Toward an understanding of short distance repulsions among baryons in QCD -- NBS wave functions and operator product expansion --

We report on our recent attempts to determine the short distance behaviors of general 2-baryon and 3-baryon forces, which are defined from the Nambu-Bethe-Salpeter(NBS) wave function, by using the operator product expansion and a renormalization group analysis in QCD. We have found that the repulsion at short distance increases as the number of valence quarks increases or when the number of different flavors involved decreases. This global tendency suggests a Pauli suppression principle among quark fields at work.Comment: 14 pages, add two exmples in sect.3.4, a version accepted for Progress of Theoretical Physic

Static quark anti-quark free energy and the running coupling at finite temperature

We analyze the free energy of a static quark anti-quark pair in quenched QCD at short and large distances. From this we deduce running couplings, g^2(r,T), and determine the length scale that separates at high temperature the short distance perturbative regime from the large distance non-perturbative regime in the QCD plasma phase. Ambiguities in the definition of a coupling beyond the perturbative regime are discussed in their relation to phenomenological considerations on heavy quark bound states in the quark gluon plasma. Our analysis suggests that it is more appropriate to characterize the non-perturbative properties of the QCD plasma phase close to T_c in terms remnants of the confinement part of the QCD force rather than a strong Coulombic force.Comment: 8 pages, 9 EPS-files, revtex

One-Loop Self Energy and Renormalization of the Speed of Light for some Anisotropic Improved Quark Actions

One-loop corrections to the fermion rest mass M_1, wave function renormalization Z_2 and speed of light renormalization C_0 are presented for lattice actions that combine improved glue with clover or D234 quark actions and keep the temporal and spatial lattice spacings, a_t and a_s, distinct. We explore a range of values for the anisotropy parameter \chi = a_s/a_t and treat both massive and massless fermions.Comment: 45 LaTeX pages with 4 postscript figure