36 research outputs found
Vector Correlators in Lattice QCD: methods and applications
We discuss the calculation of the leading hadronic vacuum polarization in
lattice QCD. Exploiting the excellent quality of the compiled experimental data
for the e^+e^- --> hadrons cross-section, we predict the outcome of
large-volume lattice calculations at the physical pion mass, and design
computational strategies for the lattice to have an impact on important
phenomenological quantities such as the leading hadronic contribution to
(g-2)mu and the running of the electromagnetic coupling constant. First, the
R(s) ratio can be calculated directly on the lattice in the threshold region,
and we provide the formulae to do so with twisted boundary conditions. Second,
the current correlator projected onto zero spatial momentum, in a Euclidean
time interval where it can be calculated accurately, provides a potentially
critical test of the experimental R(s) ratio in the region that is most
relevant for (g-2)mu. This observation can also be turned around: the vector
correlator at intermediate distances can be used to determine the lattice
spacing in fm, and we make a concrete proposal in this direction. Finally, we
quantify the finite-size effects on the current correlator coming from
low-energy two-pion states and provide a general parametrization of the vacuum
polarization on the torus.Comment: 16 pages, 9 figure files; corrected a factor 2 in Eq. (7) over the
published versio
Twisted mass lattice QCD
I review the theoretical foundations, properties as well as the simulation
results obtained so far of a variant of the Wilson lattice QCD formulation:
Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors
and on the effects of these discretization errors on the phase structure for
Wilson-like fermions in the chiral limit. The possibility to use in lattice
simulations different lattice actions for sea and valence quarks to ease the
renormalization patterns of phenomenologically relevant local operators, is
also discussed.Comment: v2. 143 pages, 28 figures. Sect. 2 now split in two sections. Several
improvements for better readability. Typos corrected. Added 2 figures. Added
references. Clarifications on few points. Conclusions and results unchanged.
Version published on Physics Repor