1,338 research outputs found
The SU(3) Beta Function from Numerical Stochastic Perturbation Theory
The SU(3) beta function is computed from Wilson loops to 20th order numerical
stochastic perturbation theory. An attempt is made to include massless
fermions, whose contribution is known analytically to 4th order. The question
whether the theory admits an infrared stable fixed point is addressed.Comment: 10 pages, 7 figures, version to be published in Physics Letters
One-loop renormalisation of quark bilinears for overlap fermions with improved gauge actions
We compute lattice renormalisation constants of local bilinear quark
operators for overlap fermions and improved gauge actions. Among the actions we
consider are the Symanzik, L\"uscher-Weisz, Iwasaki and DBW2 gauge actions. The
results are given for a variety of parameters. We show how to apply mean
field (tadpole) improvement to overlap fermions. The question, what is a good
gauge action, is discussed from the perturbative point of view. Finally, we
show analytically that the gauge dependent part of the self-energy and the
amputated Green functions are independent of the lattice fermion
representation, using either Wilson or overlap fermions.Comment: 38 pages, 5 figures, v2: Numbers in Tables 1-4,7-10 corrected, Figs.
4,5 updated, 2 misprints in (A.2), (A.4) correcte
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
Perturbatively improving renormalization constants
Renormalization factors relate the observables obtained on the lattice to
their measured counterparts in the continuum in a suitable renormalization
scheme. They have to be computed very precisely which requires a careful
treatment of lattice artifacts. In this work we present a method to suppress
these artifacts by subtracting one-loop contributions proportional to the
square of the lattice spacing calculated in lattice perturbation theory.Comment: 7 pages, 2 figures, LATTICE 201
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
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