24 research outputs found
CLS 2+1 flavor simulations at physical light- and strange-quark masses
We report recent efforts by CLS to generate an ensemble with physical light-
and strange-quark masses in a lattice volume of 192x96^3 at
corresponding to a lattice spacing of 0.064 fm. This ensemble is being
generated as part of the CLS 2+1 flavor effort with improved Wilson fermions.
Our simulations currently cover 5 lattice spacings ranging from 0.039 fm to
0.086 fm at various pion masses along chiral trajectories with either the sum
of the quark masses kept fixed, or with the strange-quark mass at the physical
value. The current status of simulations is briefly reviewed, including a short
discussion of measured autocorrelation times and of the main features of the
simulations. We then proceed to discuss the thermalization strategy employed
for the generation of the physical quark-mass ensemble and present first
results for some simple observables. Challenges encountered in the simulation
are highlighted.Comment: 7 pages, 8 figures; Proceedings, 35th International Symposium on
Lattice Field Theory (Lattice2017): Granada, Spai
and masses and decay constants
We present preliminary results for the masses and decay constants of the
and mesons using CLS ensembles. One of the
major challenges in these calculations are the large statistical fluctuations
due to disconnected quark loops. We tackle these by employing a combination of
noise reduction techniques which are tuned to minimize the statistical error at
a fixed cost. On the analysis side we carefully assess excited states
contributions by using a direct fit approach.Comment: 8 pages, 7 figures, talk presented at the 35th International
Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain. v2:
corrected axis labe
Using NSPT for the Removal of Hypercubic Lattice Artifacts
The treatment of hypercubic lattice artifacts is essential for the
calculation of non-perturbative renormalization constants of RI-MOM schemes. It
has been shown that for the RI'-MOM scheme a large part of these artifacts can
be calculated and subtracted with the help of diagrammatic Lattice Perturbation
Theory (LPT). Such calculations are typically restricted to 1-loop order, but
one may overcome this limitation and calculate hypercubic corrections for any
operator and action beyond the 1-loop order using Numerical Stochastic
Perturbation Theory (NSPT). In this study, we explore the practicability of
such an approach and consider, as a first test, the case of Wilson fermion
bilinear operators in a quenched theory. Our results allow us to compare
boosted and unboosted perturbative corrections up to the 3-loop order.Comment: 7 pages, 6 figures, talk presented at the 32nd International
Symposium on Lattice Field Theory (Lattice 2014), 23-28 June 2014, New York,
USA; PoS(LATTICE2014)29
Discretization Errors for the Gluon and Ghost Propagators in Landau Gauge using NSPT
The subtraction of hypercubic lattice corrections, calculated at 1-loop order
in lattice perturbation theory (LPT), is common practice, e.g., for
determinations of renormalization constants in lattice hadron physics.
Providing such corrections beyond 1-loop order is however very demanding in
LPT, and numerical stochastic perturbation theory (NSPT) might be the better
candidate for this. Here we report on a first feasibility check of this method
and provide (in a parametrization valid for arbitrary lattice couplings) the
lattice corrections up to 3-loop order for the SU(3) gluon and ghost
propagators in Landau gauge. These propagators are ideal candidates for such a
check, as they are available from lattice simulations to high precision and can
be combined to a renormalization group invariant product (Minimal MOM coupling)
for which a 1-loop LPT correction was found to be insufficient to remove the
bulk of the hypercubic lattice artifacts from the data. As a bonus, we also
compare our results with the ever popular H(4) method.Comment: 7 pages, 5 figures, presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
Properties of the η and η' mesons from lattice QCD
In this thesis we compute masses, decay constants and gluonic matrix elements of the flavour-diagonal pseudoscalar mesons η and η' from lattice QCD.
To control all relevant systematic errors we employ Nf = 2 + 1 flavour simulations along two distinct quark mass trajectories leading to and including the physical point. The continuum extrapolation is guided by four lattice spacings. The ensembles were generated within the coordinated lattice simulations initiative, and we set their relative scales in this work.
We discuss noise reduction techniques for the efficient calculation of the disconnected contributions that are important building blocks of the relevant correlation functions of the η and η' system. The physical states are no flavour eigenstates, and hence sophisticated analysis methods are required to extract them from the data. We develop a matrix generalization of the effective mass
method which we employ in conjunction with additional techniques to determine masses and matrix elements. The physical point extrapolation employs next-to-leading order large-Nc chiral perturbation theory, and we determine all relevant low energy constants. For the first time also their renormalization scale dependence is taken into account, and this provides an important check of the range of validity of this effective field theory with implications on many existing phenomenological analyses. Our physical point results for the masses are in agreement with experimental values and read
Mη = 554.7(9.2) MeV and Mη' = 930(21) MeV. The determination of the four η and η' decay constants is the first from first principles and we obtain F8 = 115.0(2.8) MeV and θ8 = −25.8(2.3)◦ in the octet channel and F0 = 100.1(3.0) MeV and θ0 = −8.1(1.8)◦ for the singlet in the MS scheme at 2 GeV. These results are in excellent agreement with phenomenological
determinations and at a similar level of precision.
Finally, we connect these axialvector decay constants with pseudoscalar and gluonic matrix elements to test the axial Ward identities, and predict the anomalous matrix elements to be aη = = 0.0170(10) GeV^3 and aη' = = 0.0381(84) GeV^3 at the physical point and µ = 2 GeV
Lattice simulations with improved Wilson fermions at a fixed strange quark mass
The explicit breaking of chiral symmetry of the Wilson fermion action results
in additive quark mass renormalization. Moreover, flavour singlet and
non-singlet scalar currents acquire different renormalization constants with
respect to continuum regularization schemes. This complicates keeping the
renormalized strange quark mass fixed when varying the light quark mass in
simulations with sea quark flavours. Here we present and validate our
strategy within the CLS (Coordinated Lattice Simulations) effort to achieve
this in simulations with non-perturbatively order- improved Wilson fermions.
We also determine various combinations of renormalization constants and
improvement coefficients.Comment: 18 pages, 11 Figures, V2: References added/updated, all fits rerun
with improved statistics for ensemble N204, also using the final values for
the improvement coefficients A and b_P-b_A (very minor impact), The figures
have been replotted accordingly. (The differences with respect to V1 are
invisible to the human eye). Minor change
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
Scale setting and the light baryon spectrum in QCD with Wilson fermions
We determine the light baryon spectrum on ensembles generated by the
Coordinated Lattice Simulations (CLS) effort, employing flavours of
non-perturbatively improved Wilson fermions. The hadron masses are interpolated
and extrapolated within the quark mass plane, utilizing three distinct
trajectories, two of which intersect close to the physical quark mass point and
the third one approaching the SU(3) chiral limit. The results are extrapolated
to the continuum limit, utilizing six different lattice spacings ranging from
fm down to below fm. The light pion mass varies from
MeV down to MeV. In general, the spatial extent is
kept larger than four times the inverse pion mass and larger than fm,
with additional small and large volume ensembles to investigate finite size
effects. We determine the Wilson flow scales fm and from the octet
cascade ( baryon). Determining the light baryon spectrum in the continuum
limit, we find the nucleon mass MeV and the other
stable baryon masses to agree with their experimental values within sub-percent
level uncertainties. Moreover, we determine SU(3) and SU(2) chiral perturbation
theory low energy constants, including the octet and the baryon
sigma~terms MeV,
MeV,
MeV,
MeV and
MeV, as well as various parameters,
renormalization factors and improvement coefficients that are relevant for
simulations with our lattice action.Comment: 128 pages, many figure