777 research outputs found
Instantons and Condensate
We argue that the is similar to .Comment: 6 pages, 1 fig., 1 tab., RevTeX to be use
Dynamical lattice computation of the Isgur-Wise functions Ï1/2 and Ï3/2
We perform a two-flavor dynamical lattice computation of the Isgur-Wise functions t1/2 and t3/2
at zero recoil in the static limit. We find t1/2(1) = 0.297(26) and t3/2(1) = 0.528(23) fulfilling
Uraltsevâs sum rule by around 80%. We also comment on a persistent conflict between theory and
experiment regarding semileptonic decays of B mesons into orbitally excited P wave D mesons,
the so-called â1/2 versus 3/2 puzzleâ, and we discuss the relevance of lattice results in this
context
Quark propagator and vertex: systematic corrections of hypercubic artifacts from lattice simulations
This is the first part of a study of the quark propagator and the vertex
function of the vector current on the lattice in the Landau gauge and using
both Wilson-clover and overlap actions. In order to be able to identify lattice
artifacts and to reach large momenta we use a range of lattice spacings. The
lattice artifacts turn out to be exceedingly large in this study. We present a
new and very efficient method to eliminate the hypercubic (anisotropy)
artifacts based on a systematic expansion on hypercubic invariants which are
not SO(4) invariant. A simpler version of this method has been used in previous
works. This method is shown to be significantly more efficient than the popular
``democratic'' methods. It can of course be applied to the lattice simulations
of many other physical quantities. The analysis indicates a hierarchy in the
size of hypercubic artifacts: overlap larger than clover and propagator larger
than vertex function. This pleads for the combined study of propagators and
vertex functions via Ward identities.Comment: 14 pags., 9 fig
Testing OPE for ghosts, gluons and
We present here our results on extracting Wilson coefficients from different
quantities such as ghost and gluon propagators which are calculated by means of
Lattice QCD. The results confirm the validity of our method for the calculation
of the strong coupling constant as well as allow to estimate the range of
momenta where OPE is applicable.Comment: arXiv admin note: substantial text overlap with arXiv:1301.759
Suppressed decay into open charm for the Y(4260) being an hybrid
We investigate the Y(4260) resonance recently discovered by the Babar
collaboration. We propose the observation of its decay into J/psi pi pi and its
non observation into open charm as a consequence of it being a charmonium
hybrid state with a magnetic constituent gluon. We prove a selection rule
forbidding its decay into two S-wave charmed mesons in any potential model. We
suggest a generalisation of the selection rule based only on the heavy quark
nature of the charm.Comment: 5 page
The strong coupling constant at small momentum as an instanton detector
We present a study of at small p computed from the lattice.
It shows a dramatic law which can be understood within an
instanton liquid model. In this framework the prefactor gives a direct measure
of the instanton density in thermalised configurations. A preliminary result
for this density is 5.27(4) fm^{-4}.Comment: 12 pages, 4 figure
Renormalization constants for twisted mass QCD
We summarize recent non-perturbative results obtained for the renormalization
constants computed in the RI'-MOM scheme for twisted mass
QCD. Our implementation employs the Iwasaki gauge action and four dynamical
degenerate twisted mass fermions. Renormalization constants for scalar,
pseudo-scalar, vector and axial operators, as well as the quark propagator
renormalization, are computed at three different values of the lattice spacing,
two different volumes and several values of the twisted mass. Our method allows
for a precise cross-check of the running, because of the particular proper
treatment of the hypercubic artifacts. Preliminary results for twist-2
operators are also presented
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