1,741 research outputs found
Renormalization constants of local operators within the Schr\"odinger functional scheme
We define, within the Schr\"odinger functional (SF) scheme, the matrix
elements of the twist-2 operators corresponding to the first two moments of
non-singlet parton density, and the first moment of singlet parton densities.
We perform a lattice one-loop calculation that fixes the relation between the
SF scheme and other common schemes and shows the main source of lattice
artefacts. Few remarks on the improvement case are added.Comment: Presented at LATTICE99, 3 page
Perturbative Renormalization of Improved Lattice Operators
We derive bases of improved operators for all bilinear quark currents up to
spin two (including the operators measuring the first moment of DIS Structure
Functions), and compute their one-loop renormalization constants for arbitrary
coefficients of the improvement terms. We have thus control over O(a)
corrections, and for a suitable choice of improvement coefficients we are only
left with errors of O(a^2).Comment: 4 pages, LaTeX + 1 eps file + epscrc2.sty (included). Talk given to
the Lattice 97 International Symposium, 22-26 July 1997, Edinburgh, UK. Minor
changes in notatio
Large pion pole in Z_{S}^{MOM}/Z_{P}^{MOM} from Wilson action data
We show that, contrarily to recent claims, data from the Wilson (unimproved)
fermionic action at three different beta values demonstrate the presence of a
large Goldstone boson contribution in the quark pseudoscalar vertex,
quantitatively close to our previous estimate based on the SW action with
c_{SW}=1.769. We show that discretisation errors on Z_{S}^{MOM}/Z_{P}^{MOM}
seem to be much smaller than the Goldstone pole contribution over a very large
range of momenta. The subtraction of this non perturbative contribution leads
to numbers close to one-loop BPT.Comment: 12 pages, 5 figures, laTeX, minor corrections of typos, beta
dependence made more explicit, added one table giving the contribution of the
Goldstone vs. the discretisation errors at ap=
3-point functions from twisted mass lattice QCD at small quark masses
We show at the example of the matrix element between pion states of a
twist-2, non-singlet operator that Wilson twisted mass fermions allow to
compute this phenomenologically relevant quantitiy at small pseudo scalar
masses of O(270 MeV). In the quenched approximation, we investigate the scaling
behaviour of this observable that is derived from a 3-point function by
applying two definitions of the critical mass and find a scaling compatible
with the expected O(a^2) behaviour in both cases. A combined continuum
extrapolations allows to obtain reliable results at small pion masses, which
previously could not be explored by lattice QCD simulations.Comment: 6 pages, 2 figures, talk presented at Lattice 200
Renormalization of minimally doubled fermions
We investigate the renormalization properties of minimally doubled fermions,
at one loop in perturbation theory. Our study is based on the two particular
realizations of Borici-Creutz and Karsten-Wilczek. A common feature of both
formulations is the breaking of hyper-cubic symmetry, which requires that the
lattice actions are supplemented by suitable counterterms. We show that three
counterterms are required in each case and determine their coefficients to one
loop in perturbation theory. For both actions we compute the vacuum
polarization of the gluon. It is shown that no power divergences appear and
that all contributions which arise from the breaking of Lorentz symmetry are
cancelled by the counterterms. We also derive the conserved vector and
axial-vector currents for Karsten-Wilczek fermions. Like in the case of the
previously studied Borici-Creutz action, one obtains simple expressions,
involving only nearest-neighbour sites. We suggest methods how to fix the
coefficients of the counterterms non-perturbatively and discuss the
implications of our findings for practical simulations.Comment: 23 pages, 1 figur
Moments of Structure Functions in Full QCD
Moments of the quark density distribution, moments of the quark helicity
distribution, and the tensor charge are calculated in full QCD. Calculations of
matrix elements of operators from the operator product expansion have been
performed on lattices for Wilson fermions at
using configurations from the SESAM collaboration and at using
configurations from SCRI. One-loop perturbative renormalization corrections are
included. Selected results are compared with corresponding quenched
calculations and with calculations using cooled configurations.Comment: Lattice 2000 (Hadronic Matrix Elements), 4 pages, 5 figure
Moments of parton evolution probabilities on the lattice within the Schroedinger functional scheme
We define, within the Schroedinger functional scheme (SF), the matrix
elements of the twist-2 operators corresponding to the first two moments of
non-singlet parton densities. We perform a lattice one-loop calculation that
fixes the relation between the SF scheme and other common schemes and shows the
main source of lattice artefacts. This calculation sets the basis for a
numerical evaluation of the non-perturbative running of parton densities.Comment: Latex file, 4 figures, 15 page
Higher-Twist Contribution to Pion Structure Function: 4-Fermi Operators
We present quenched lattice QCD results for the contribution of higher-twist
operators to the lowest non-trivial moment of the pion structure function. To
be specific, we consider the combination which has and receives contributions from 4-Fermi
operators only. We introduce the basis of lattice operators. The
renormalization of the operators is done perturbatively in the
scheme using the 't Hooft-Veltman prescription for , taking
particular care of mixing effects. The contribution is found to be of
, relative to the leading contribution to the moment of
.Comment: Version to appear in Nucl. Phys.
Power Corrections to Perturbative QCD and OPE in Gluon Green Functions
We show that QCD Green functions in Landau Gauge exhibit sizable
corrections to the expected perturbative behavior at energies as high as 10
GeV. We argue that these are due to a -condensate which does not vanish
in Landau gauge.Comment: 3 pages 1 figure lattice2001 (gaugetheories
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