59 research outputs found
Unstable particles in finite volume: The broken phase of the -d non-linear -model
According to a proposal of L\"uscher it is possible to determine elastic
scattering phases in infinite volume from the energy spectrum of two-particle
states in a periodic box.
We demonstrate the applicability of this method in the broken phase of the
4-dimensional non-linear -model in a Monte-Carlo study on finite
lattices.
This non-perturbative approach also permits the study of unstable particles,
the \sg-particle in our case. We observe the \sg-resonance and extract its
mass and its width.Comment: 4 pages LaTeX, 4 PS figures, LATTICE'92 contributio
and resonances on the lattice at nearly physical quark masses and
Working with a pion mass MeV, we study and
scattering using two flavours of non-perturbatively improved Wilson
fermions at a lattice spacing fm. Employing two lattice
volumes with linear spatial extents of and points and moving
frames, we extract the phase shifts for p-wave and scattering
near the and resonances.Comparing our results to those of previous
lattice studies, that used pion masses ranging from about 200 MeV up to 470
MeV, we find that the coupling appears to be remarkably
constant as a function of .Comment: 16 pages, 8 figures, v2: "and " added to the title, references
updated, some figures replaced, including improved summary plots, alternative
parametrizations are considered and analytical continations are performed to
determine pole positions on the second Riemann shee
Pion and Kaon Distribution Amplitudes from lattice QCD: towards the continuum limit
We present the current status of a non-perturbative lattice calculation of
the moments of the pion and kaon distribution amplitudes by the RQCD
collaboration. Our investigation is carried out using dynamical,
non-perturbatively O(a)-improved Wilson fermions on the CLS ensembles with 5
different lattice spacings and pion masses down to the physical pion mass. A
combined continuum and chiral extrapolation to the physical point is performed
along two independent quark mass trajectories simultaneously. We employ
momentum smearing in order to decrease the contamination by excited states and
increase statistical precision.Comment: Proceedings of the 36th Annual International Symposium on Lattice
Field Theory - LATTICE201
Scattering phases in the broken phase of the 4-d O(4) non-linear sigma-model
Using Luescher's method we determine the elastic scattering phases in the
broken phase of the 4-dimensional O(4) non-linear sigma-model from the
two-particle energy spectrum in a Monte-Carlo study on finite lattices. In the
isospin-0-channel we observe the sigma-resonance and extract its mass and its
width. In all scattering channels investigated the results are consistent with
perturbative calculations.Comment: 3 pages, talk presented at Lattice 199
Nucleon generalized form factors from two-flavor lattice QCD
We determine the generalized form factors, which correspond to the second Mellin moment (i.e., the first x-moment) of the generalized parton distributions of the nucleon at leading twist. The results are obtained using lattice QCD with N-f = 2 nonperturbatively improved Wilson fermions, employing a range of quark masses down to an almost physical value with a pion mass of about 150 MeV. We also present results for the isovector quark angular momentum and for the first x-moment of the transverse quark spin density. We compare two different fit strategies and find that directly fitting the ground state matrix elements to the functional form expected from Lorentz invariance and parametrized in terms of form factors yields comparable, and usually more stable results than the traditional approach where the form factors are determined from an overdetermined linear system based on the fitted matrix elements
Light-cone distribution amplitudes of the baryon octet
We present results of the first ab initio lattice QCD calculation of the
normalization constants and first moments of the leading twist distribution
amplitudes of the full baryon octet, corresponding to the small transverse
distance limit of the associated S-wave light-cone wave functions. The P-wave
(higher twist) normalization constants are evaluated as well. The calculation
is done using flavors of dynamical (clover) fermions on lattices of
different volumes and pion masses down to 222 MeV. Significant SU(3) flavor
symmetry violation effects in the shape of the distribution amplitudes are
observed.Comment: Update to the version published in JHE
Light-cone distribution amplitudes of octet baryons from lattice QCD
We present lattice QCD results for the wave function normalization constants
and the first moments of the distribution amplitudes for the lowest-lying
baryon octet. The analysis is based on a large number of ensembles
comprising multiple trajectories in the quark mass plane including physical
pion (and kaon) masses, large volumes, and, most importantly, five different
lattice spacings down to . This allows us to perform a
controlled extrapolation to the continuum and infinite volume limits by a
simultaneous fit to all available data. We demonstrate that the formerly
observed violation of flavor symmetry breaking constraints can, indeed, be
attributed to discretization effects that vanish in the continuum limit
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