46 research outputs found
Perturbative renormalisation of quark bilinear operators for overlap fermions with and without stout links and improved gauge action
We calculate lattice renormalisation constants of local and one-link quark
operators for overlap fermions and improved gauge actions in one-loop
perturbation theory. For the local operators we stout smear the SU(3) links in
the fermionic action. Using the popular tadpole improved L\"uscher-Weisz
actions at and we present numerical values for the Z
factors in the scheme (partly as function of the stout smearing
strength). We compare various levels of mean field (tadpole) improvement which
have been applied to our results.Comment: 7 page
Non-perturbative renormalisation for overlap fermions
Using non-perturbative techniques we have found the renormalisation factor,
Z, in the RI-MOM scheme for quark bilinear operators in quenched QCD. We worked
with overlap fermions using the Luescher-Weisz gauge action. Our calculation
was performed at beta=8.45 at a lattice spacing of 1/a=2.1 GeV using a value of
rho=1.4. Our results show good agreement between the vector and the axial
vector in the zero mass limit. This shows that overlap fermions have good
chiral properties. To attempt to improve the discretisation errors in our
results we subtracted the O(a^2) terms in one-loop lattice perturbation theory
from the Monte Carlo Green functions. In particular we paid attention to the
operators for the observable . We found a value for the renormalisation
constants Z^msbar_(v_2b) and Z^msbar_(v_2a) just less than 1.9 at mu=1/a=2.1
GeV.Comment: 6 pages, 3 figures, uses PoS style, poster presented at Lattice 2005
(Chiral Fermions), to be published in Proceedings of Scienc
Accelerating Hasenbusch's acceleration of Hybrid Monte Carlo
Hasenbusch has proposed splitting the pseudo-fermionic action into two parts,
in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a
different splitting, also using clover-improved Wilson fermions. An additional
speed-up between 5 and 20% over the original proposal was achieved in
production runs.Comment: Poster presented by H. Stueben at Lattice2003, meta-data correcte
Determination of the strange nucleon form factors
The strange contribution to the electric and magnetic form factors of the
nucleon is determined at a range of discrete values of up to
GeV. This is done by combining recent lattice QCD results for the
electromagnetic form factors of the octet baryons with experimental
determinations of those quantities. The most precise result is a small negative
value for the strange magnetic moment: . At
larger values of both the electric and magnetic form factors are
consistent with zero to within -sigma
Reduced critical slowing down for statistical physics simulations
Wang-Landau simulations offer the possibility to integrate explicitly over a collective coordinate and stochastically over the remainder of configuration space. We propose to choose the so-called "slow mode", which is responsible for large autocorrelation times and thus critical slowing down, for collective integration. We study this proposal for the Ising model and the LLR method as simulation algorithm. We firstly show that in a phase with spontaneously broken global symmetry, autocorrelation times grow exponentially with system size for the standard heatbath update. Identifying the magnetisation as collective coordinate, we present evidence that critical slowing down is absent for almost all observables
Reply to "Comment on `Lattice determination of Sigma - Lambda mixing' "
In this Reply, we respond to the above Comment. Our computation [Phys. Rev. D
91 (2015) 074512] only took into account pure QCD effects, arising from quark
mass differences, so it is not surprising that there are discrepancies in
isospin splittings and in the Sigma - Lambda mixing angle. We expect that these
discrepancies will be smaller in a full calculation incorporating QED effects.Comment: 5 page
Charge Symmetry Violation in the Electromagnetic Form Factors of the Proton
Experimental tests of QCD through its predictions for the strange-quark
content of the proton have been drastically restricted by our lack of knowledge
of the violation of charge symmetry (CSV). We find unexpectedly tiny CSV in the
proton's electromagnetic form factors by performing the first extraction of
these quantities based on an analysis of lattice QCD data. The resulting values
are an order of magnitude smaller than current bounds on proton strangeness
from parity violating electron-proton scattering experiments. This result paves
the way for a new generation of experimental measurements of the proton's
strange form factors to challenge the predictions of QCD
The nucleon mass in N_f=2 lattice QCD: finite size effects from chiral perturbation theory
In the framework of relativistic SU(2)_f baryon chiral perturbation theory we
calculate the volume dependence of the nucleon mass up to and including O(p^4).
Since the parameters in the resulting finite size formulae are fixed from the
pion mass dependence of the large volume nucleon masses and from phenomenology,
we obtain a parameter-free prediction of the finite size effects. We present
mass data from the recent N_f=2 simulations of the UKQCD and QCDSF
collaborations and compare these data as well as published mass values from the
dynamical simulations of the CP-PACS and JLQCD collaborations with the
theoretical expectations. Remarkable agreement between the lattice data and the
predictions of chiral perturbation theory in a finite volume is found.Comment: 23 pages, 5 figures; references added + minor corrections; one more
reference added, typo in eq.(25) corrected, additional clarifying remark
Exploring interpolating momentum schemes
We compute the renormalisation factors of the quark mass and wave function
using IMOM (Interpolating MOMenta) schemes. The framework is the
Rome-Southampton non-renormalisation method, but the momentum transfer in the
quark bilinears is not restricted to zero or to the symmetric point. We study
the scale dependence, infrared contamination and lattice artefacts for
different values of this momentum transfer and for two different kinds of
projectors. For the numerical simulations, we use data generated by the
RBC-UKQCD collaborations, with flavours of Domain-Wall fermions,
and inverse lattice spacing of and GeV.Comment: Talk presented at the 38th International Symposium on Lattice Field
Theory, LATTICE2021 26th-30th July, 2021 Zoom/Gather@Massachusetts Institute
of Technolog
Axial and tensor charge of the nucleon with dynamical fermions
We present preliminary results for the axial and tensor charge of the nucleon
obtained from simulations with N_f=2 clover fermions. A comparison with chiral
perturbation theory is attempted.Comment: Talk presented at Lattice2004(weak), Fermilab, June 21-26, 2004, 3
pages, 3 figures, v2: one reference added, v3: acknowledgement extende