2,044 research outputs found
Unquenched Numerical Stochastic Perturbation Theory
The inclusion of fermionic loops contribution in Numerical Stochastic
Perturbation Theory (NSPT) has a nice feature: it does not cost so much
(provided only that an FFT can be implemented in a fairly efficient way).
Focusing on Lattice SU(3), we report on the performance of the current
implementation of the algorithm and the status of first computations
undertaken.Comment: 3 pages, 3 figures, Lattice2002(algor
Two and three loops computations of renormalization constants for lattice QCD
Renormalization constants can be computed by means of Numerical Stochastic
Perturbation Theory to two/three loops in lattice perturbation theory, both in
the quenched approximation and in the full (unquenched) theory. As a case of
study we report on the computation of renormalization constants of the
propagator for Wilson fermions. We present our unquenched (N_f=2) computations
and compare the results with non perturbative determinations.Comment: Lattice2004(improv), 3 pages, 4 figure
Numerical Stochastic Perturbation Theory. Convergence and features of the stochastic process. Computations at fixed (Landau) Gauge
Concerning Numerical Stochastic Perturbation Theory, we discuss the
convergence of the stochastic process (idea of the proof, features of the limit
distribution, rate of convergence to equilibrium). Then we also discuss the
expected fluctuations in the observables and give some idea to reduce them. In
the end we show that also computation of quantities at fixed (Landau) Gauge is
now possible.Comment: 3 pages. Contributed to 17th International Symposium on Lattice Field
Theory (LATTICE 99), Pisa, Italy, 29 Jun - 3 Jul 199
Beta-function, Renormalons and the Mass Term from Perturbative Wilson Loops
Several Wilson loops on several lattice sizes are computed in Perturbation
Theory via a stochastic method. Applications include: Renormalons, the Mass
Term in Heavy Quark Effective Theory and (possibly) the beta-function.Comment: 3 pages, 1 eps figure. Contributed to 17th International Symposium on
Lattice Field Theory (LATTICE 99), Pisa, Italy, 29 Jun - 3 Jul 199
3-d lattice SU(3) free energy to four loops
We report on the perturbative computation of the 3d lattice Yang-Mills free
energy to four loops by means of Numerical Stochastic Perturbation Theory. The
known first and second orders have been correctly reproduced; the third and
fourth order coefficients are new results and the known logarithmic IR
divergence in the fourth order has been correctly identified. Progress is being
made in switching to the gluon mass IR regularization and the related inclusion
of the Faddeev-Popov determinant.Comment: Lattice2004(non-zero), 3 pages, 2 figure
Numerical Stochastic Perturbation Theory for full QCD
We give a full account of the Numerical Stochastic Perturbation Theory method
for Lattice Gauge Theories. Particular relevance is given to the inclusion of
dynamical fermions, which turns out to be surprisingly cheap in this context.
We analyse the underlying stochastic process and discuss the convergence
properties. We perform some benchmark calculations and - as a byproduct - we
present original results for Wilson loops and the 3-loop critical mass for
Wilson fermions.Comment: 35 pages, 5 figures; syntax revise
A consistency check for Renormalons in Lattice Gauge Theory: beta^(-10) contributions to the SU(3) plaquette
We compute the perturbative expansion of the Lattice SU(3) plaquette to
beta^(-10) order. The result is found to be consistent both with the expected
renormalon behaviour and with finite size effects on top of that.Comment: 15 pages, 5 colour eps figures. Axes labels added in the figures. A
comment added in the appendi
The Dirac operator spectrum: a perturbative approach
By computing the Dirac operator spectrum by means of Numerical Stochastic
Perturbation Theory, we aim at throwing some light on the widely accepted
picture for the mechanism which is behind the Bank-Casher relation. The latter
relates the chiral condensate to an accumulation of eigenvalues in the low end
of the spectrum. This can be in turn ascribed to the usual mechanism of
repulsion among eigenvalues which is typical of quantum interactions. First
results appear to confirm that NSPT can indeed enable us to inspect a huge
reshuffling of eigenvalues due to quantum repulsion.Comment: 8 pages, 6 figures; talk presented at the 27th International
Symposium on Lattice Field Theory (Lattice 2009), Beijing, China, 26-31 Jul
200
Thimble regularization at work for Gauge Theories: from toy models onwards
A final goal for thimble regularization of lattice field theories is the
application to lattice QCD and the study of its phase diagram. Gauge theories
pose a number of conceptual and algorithmic problems, some of which can be
addressed even in the framework of toy models. We report on our progresses in
this field, starting in particular from first successes in the study of one
link models.Comment: 7 pages, 2 figures. Talk given at the Lattice2015 Conferenc
- …