1,138 research outputs found
Non perturbative determination of the running coupling constant in quenched SU(2)
Through a finite size renormalization group technique we calculate the
running coupling constant for quenched SU(2) with a few percent error over a
range of energy varying by a factor thirty. The definition is based on ratio of
correlations of Polyakov loops with twisted boundary conditions. The
extrapolation to the continuum limit is governed by corrections due to lattice
artifacts which are proportional to the square of the lattice spacing and
appears rather smooth.Comment: 18 pages of ps fil
Leading Quenching Effects in the Proton Magnetic Moment
We present the first investigation of the extrapolation of quenched nucleon
magnetic moments in quenched chiral effective field theory. We utilize
established techniques in finite-range regularisation and compare with standard
dimensional regularisation methods. Finite-volume corrections to the relevant
loop integrals are also addressed. Finally, the contributions of dynamical sea
quarks to the proton moment are estimated using a recently discovered
phenomenological link between quenched and physical QCD.Comment: 9 pages, 11 figs; v2: revised finite volume discussio
On the discretization of physical momenta in lattice QCD
The adoption of two distinct boundary conditions for two fermions species on
a finite lattice allows to deal with arbitrary relative momentum between the
two particle species, in spite of the momentum quantization rule due to a
limited physical box size. We test the physical significance of this
topological momentum by checking in the continuum limit the validity of the
expected energy-momentum dispersion relations.Comment: 9 pages, 3 figures; references added; no changes in text or results;
version accepted for pubblication in Phys. Lett.
Hybrid meson decay from the lattice
We discuss the allowed decays of a hybrid meson in the heavy quark limit. We
deduce that an important decay will be into a heavy quark non-hybrid state and
a light quark meson, in other words, the de-excitation of an excited gluonic
string by emission of a light quark-antiquark pair.
We discuss the study of hadronic decays from the lattice in the heavy quark
limit and apply this approach to explore the transitions from a spin-exotic
hybrid to and where is a scalar meson. We obtain a
signal for the transition emitting a scalar meson and we discuss the
phenomenological implications.Comment: 18 pages, LATEX, 3 ps figure
QCD and String Theory
This talk begins with some history and basic facts about string theory and
its connections with strong interactions. Comparisons of stacks of Dirichlet
branes with curved backgrounds produced by them are used to motivate the
AdS/CFT correspondence between superconformal gauge theory and string theory on
a product of Anti-de Sitter space and a compact manifold. The ensuing duality
between semi-classical spinning strings and long gauge theory operators is
briefly reviewed. Strongly coupled thermal SYM theory is explored via a black
hole in 5-dimensional AdS space, which leads to explicit results for its
entropy and shear viscosity. A conjectured universal lower bound on the
viscosity to entropy density ratio, and its possible relation to recent results
from RHIC, are discussed. Finally, some available results on string duals of
confining gauge theories are briefly reviewed.Comment: 12 pages, prepared for the Proceedings of the 2005 Lepton-Photon
Symposium; v2: minor revisions, references added, the version to appear in
the proceeding
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