56 research outputs found
Towards a new determination of the QCD Lambda parameter from running couplings in the three-flavour theory
We review our new strategy and current status towards a high precision
computation of the Lambda parameter from three-flavour simulations in QCD. To
reach this goal we combine specific advantages of the Schr\"odinger functional
and gradient flow couplings.Comment: 7 pages, 3 figures; Proceedings of the 32nd International Symposium
on Lattice Field Theory; 23-28 June, 2014, Columbia University, New Yor
The -parameter in 3-flavour QCD and by the ALPHA collaboration
We present results by the ALPHA collaboration for the -parameter in
3-flavour QCD and the strong coupling constant at the electroweak scale,
, in terms of hadronic quantities computed on the CLS gauge
configurations. The first part of this proceedings contribution contains a
review of published material \cite{Brida:2016flw,DallaBrida:2016kgh} and yields
the -parameter in units of a low energy scale, . We
then discuss how to determine this scale in physical units from experimental
data for the pion and kaon decay constants. We obtain MeV which translates to
using perturbation theory to match between 3-, 4- and 5-flavour QCD.Comment: 21 pages. Collects contributions of A. Ramos, S. Sint and R. Sommer
to the 34th annual International Symposium on Lattice Field Theory; LaTeX
input encoding problem fixe
Fermion loop simulation of the lattice Gross-Neveu model
We present a numerical simulation of the Gross-Neveu model on the lattice
using a new representation in terms of fermion loops. In the loop
representation all signs due to Pauli statistics are eliminated completely and
the partition function is a sum over closed loops with only positive weights.
We demonstrate that the new formulation allows to simulate volumes which are
two orders of magnitude larger than those accessible with standard methods
Renormalization constants of local operators for Wilson type improved fermions
Perturbative and non-perturbative results are presented on the
renormalization constants of the quark field and the vector, axial-vector,
pseudoscalar, scalar and tensor currents. The perturbative computation, carried
out at one-loop level and up to second order in the lattice spacing, is
performed for a fermion action, which includes the clover term and the twisted
mass parameter yielding results that are applicable for unimproved Wilson
fermions, as well as for improved clover and twisted mass fermions. We consider
ten variants of the Symanzik improved gauge action corresponding to ten
different values of the plaquette coefficients. Non-perturbative results are
obtained using the twisted mass Wilson fermion formulation employing two
degenerate dynamical quarks and the tree-level Symanzik improved gluon action.
The simulations are performed for pion masses in the range of 480 MeV to 260
MeV and at three values of the lattice spacing, a, corresponding to beta=3.9,
4.05, 4.20. For each renormalization factor computed non-perturbatively we
subtract its perturbative O(a^2) terms so that we eliminate part of the cut-off
artifacts. The renormalization constants are converted to MS-bar at a scale of
mu=2 GeV. The perturbative results depend on a large number of parameters and
are made easily accessible to the reader by including them in the distribution
package of this paper, as a Mathematica input file.Comment: 36 pages, 11 figures and 6 tables. The results are included in
electronic form (Mathematica files
Nucleon form factors with dynamical twisted mass fermions
The electromagnetic and axial form factors of the nucleon are evaluated in
twisted mass QCD with two degenerate flavors of light, dynamical quarks. The
axial charge g_A, magnetic moment and the Dirac and Pauli radii are determined
for pion masses in the range 300 MeV to 500 MeV
Nucleon form factors with Nf=2 dynamical twisted mass fermions
We present results on the electromagnetic and axial nucleon form factors
using two degenerate flavors of twisted mass fermions on lattices of spatial
size 2.1 fm and 2.7 fm and a lattice spacing of about 0.09 fm. We consider pion
masses in the range of 260-470 MeV. We chirally extrapolate results on the
nucleon axial ch arge, the isovector Dirac and Pauli root mean squared radii
and magnetic moment to the physical point and co mpare to experiment.Comment: Report no. added; typos corrected. ETM Collaboration, 7 pages, 10
figures, Talk given at the XXVII International Symposium on Lattice Field
Theory - LAT2009, July 26-31 2009, Peking University, Beijing, Chin
The low-lying baryon spectrum with two dynamical twisted mass fermions
The masses of the low lying baryons are evaluated using two degenerate
flavors of twisted mass sea quarks corresponding to pseudo scalar masses in the
range of about 270-500 MeV. The strange valence quark mass is tuned to
reproduce the mass of the kaon in the physical limit. The tree-level Symanzik
improved gauge action is employed. We use lattices of spatial size 2.1 fm and
2.7 fm at two values of the lattice spacing with and
. We check for both finite volume and cut-off effects on the
baryon masses. We performed a detailed study of the chiral extrapolation of the
octet and decuplet masses using SU(2) PT. The lattice spacings determined
using the nucleon mass at the physical point are consistent with the values
extracted using the pion decay constant. We examine the issue of isospin
symmetry breaking for the octet and decuplet baryons and its dependence on the
lattice spacing. We show that in the continuum limit isospin breaking is
consistent with zero, as expected. The baryon masses that we find after taking
the continuum limit and extrapolating to the physical limit are in good
agreement with experiment.Comment: By the ETM Collaboration, 24 pages, 24 figure
Charmonium Spectrum from Lattice QCD
We produced a set of gauge configurations generated with a new massive renormalization scheme for three degenerate light quarks with a mass that equals the average light-quark mass in nature and a physical charm-quark mass, and a non-perturbatively determined clover coefficient for dynamical Wilson quarks on the lattice. We present the details of the algorithmic setup and tuning procedure of ensembles with three different volumes. We discuss finite volume effects and lattice artifacts, and present physical results for the charmonium spectrum and dimensionless quantities in a first continuum limit study
- âŠ