358 research outputs found
Improving the lattice axial vector current
For Wilson and clover fermions traditional formulations of the axial vector
current do not respect the continuum Ward identity which relates the divergence
of that current to the pseudoscalar density. Here we propose to use a
point-split or one-link axial vector current whose divergence exactly satisfies
a lattice Ward identity, involving the pseudoscalar density and a number of
irrelevant operators. We check in one-loop lattice perturbation theory with
SLiNC fermion and gauge plaquette action that this is indeed the case including
order effects. Including these operators the axial Ward identity remains
renormalisation invariant. First preliminary results of a nonperturbative check
of the Ward identity are also presented.Comment: 7 pages, 3 figures, Proceedings of the 33rd International Symposium
on Lattice Field Theory, 14-18 July 2015, Kobe, Japa
Renormalization of local quark-bilinear operators for Nf=3 flavors of SLiNC fermions
The renormalization factors of local quark-bilinear operators are computed
non-perturbatively for flavors of SLiNC fermions, with emphasis on the
various procedures for the chiral and continuum extrapolations. The simulations
are performed at a lattice spacing fm, and for five values of the
pion mass in the range of 290-465 MeV, allowing a safe and stable chiral
extrapolation. Emphasis is given in the subtraction of the well-known pion pole
which affects the renormalization factor of the pseudoscalar current. We also
compute the inverse propagator and the Green's functions of the local bilinears
to one loop in perturbation theory. We investigate lattice artifacts by
computing them perturbatively to second order as well as to all orders in the
lattice spacing. The renormalization conditions are defined in the RI-MOM
scheme, for both the perturbative and non-perturbative results. The
renormalization factors, obtained at different values of the renormalization
scale, are translated to the scheme and are evolved
perturbatively to 2 GeV. Any residual dependence on the initial renormalization
scale is eliminated by an extrapolation to the continuum limit. We also study
the various sources of systematic errors.
Particular care is taken in correcting the non-perturbative estimates by
subtracting lattice artifacts computed to one loop perturbation theory using
the same action. We test two different methods, by subtracting either the
contributions, or the complete (all orders in )
one-loop lattice artifacts.Comment: 33 pages, 27 figures, 6 table
Meson decay constants from Nf=2 clover fermions
We present recent results for meson decay constants calculated on
configurations with two flavours of O(a)-improved Wilson fermions.
Non-perturbative renormalisation is applied and quark mass dependencies as well
as finite volume and discretisation effects are investigated. In this work we
also present a computation of the coupling of the light vector mesons to the
tensor current using dynamical fermions.Comment: 6 pages, contribution to Lattice2005(Hadron spectrum and quark
masses
A determination of the strange quark mass for unquenched clover fermions using the AWI
Using the O(a) Symanzik improved action an estimate is given for the strange
quark mass for unquenched (nf=2) QCD. The determination is via the axial Ward
identity (AWI) and includes a non-perturbative evaluation of the
renormalisation constant. Numerical results have been obtained at several
lattice spacings, enabling the continuum limit to be taken. Results indicate a
value for the strange quark mass (in the MSbar-scheme at a scale of 2GeV) in
the range 100 - 130MeV.Comment: 6 pages, contribution to Lattice2005(Hadron spectrum and quark
masses), uses PoS.cl
Generalized Parton Distributions in Full Lattice QCD
We present recent results on generalized parton distributions from dynamical
lattice QCD calculations. Our set of twelve different combinations of couplings
and quark masses allows for a preliminary study of the pion mass dependence of
the transverse nucleon structure.Comment: 8 pages, 5 figures; Talk presented by Ph.H. at Light-Cone 2004,
Amsterdam, 16 - 20 Augus
Scattering phases for meson and baryon resonances on general moving-frame lattices
A proposal by L\"uscher enables one to compute the scattering phases of
elastic two-body systems from the energy levels of the lattice Hamiltonian in a
finite volume. In this work we generalize the formalism to S--, P-- and D--wave
meson and baryon resonances, and general total momenta. Employing nonvanishing
momenta has several advantages, among them making a wider range of energy
levels accessible on a single lattice volume and shifting the level crossing to
smaller values of .Comment: 41 pages, 3 figures. References added, minor edits to text. Version
to be published in Phys. Rev.
In-vivo data support equivalent therapeutic efficacy of a new tobramycin inhalation solution (150 mg/1.5 ml) administered by the eFlow® electronic nebuliser compared to TOBI® in the PARI LC PLUS®
The operator product expansion on the lattice
We investigate the Operator Product Expansion (OPE) on the lattice by
directly measuring the product (where J is the vector current) and
comparing it with the expectation values of bilinear operators. This will
determine the Wilson coefficients in the OPE from lattice data, and so give an
alternative to the conventional methods of renormalising lattice structure
function calculations. It could also give us access to higher twist quantities
such as the longitudinal structure function F_L = F_2 - 2 x F_1. We use overlap
fermions because of their improved chiral properties, which reduces the number
of possible operator mixing coefficients.Comment: 7 pages, 4 postscript figures. Contribution to Lattice 2007,
Regensbur
Generalized Parton Distributions from Lattice QCD
We perform a quenched lattice calculation of the first moment of twist-two
generalized parton distribution functions of the proton, and assess the total
quark (spin and orbital angular momentum) contribution to the spin of the
proton.Comment: 11 pages, 4 figures; final version, to be published in Phys. Rev.
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