1,569 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
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 n_f=2 residual mass in lattice HQET to alpha^3 order
We compute the so called residual mass in Lattice Heavy Quark Effective
Theory to alpha^3 order in the n_f=2 (unquenched) case. The control of this
additive mass renormalization is crucial for the determination of the heavy
quark mass from lattice simulations. We discuss the impact on an unquenched
determination of the b-quark mass.Comment: Lattice2004(heavy), 3 pages, 1 figur
Fermionic Loops in Numerical Stochastic Perturbation Theory
We discuss the inclusion of fermionic loops contributions in Numerical
Stochastic Perturbation Theory for Lattice Gauge Theories. We show how the
algorithm implementation is in principle straightforward and report on the
status of the project.Comment: Lattice 2000 (Perturbation Theory), 4 pages, (misprint corrected
High loop renormalization constants for Wilson fermions/Symanzik improved gauge action
We present the current status of our computation of quark bilinear
renormalization constants for Wilson fermions and Symanzik improved gauge
action. Computations are performed in Numerical Stochastic Perturbation Theory.
Volumes range from 10^4 to 32^4. Renormalization conditions are those of the
RI'-MOM scheme, imposed at different values of the physical scale. Having
measurements available at several momenta, irrelevant effects are taken into
account by means of hypercubic symmetric Taylor expansions. Finite volumes
effects are assessed repeating the computations at different lattice sizes. In
this way we can extrapolate our results to the continuum limit, in infinite
volume.Comment: 8 pages, 3 figures, talk presented at the 27th International
Symposium on Lattice Field Theory (Lattice 2009), Beijing, China, 26-31 Jul
200
Lattice gluodynamics at negative g^2
We consider Wilson's SU(N) lattice gauge theory (without fermions) at
negative values of beta= 2N/g^2 and for N=2 or 3. We show that in the limit
beta -> -infinity, the path integral is dominated by configurations where links
variables are set to a nontrivial element of the center on selected non
intersecting lines. For N=2, these configurations can be characterized by a
unique gauge invariant set of variables, while for N=3 a multiplicity growing
with the volume as the number of configurations of an Ising model is observed.
In general, there is a discontinuity in the average plaquette when g^2 changes
its sign which prevents us from having a convergent series in g^2 for this
quantity. For N=2, a change of variables relates the gauge invariant
observables at positive and negative values of beta. For N=3, we derive an
identity relating the observables at beta with those at beta rotated by +-
2pi/3 in the complex plane and show numerical evidence for a Ising like first
order phase transition near beta=-22. We discuss the possibility of having
lines of first order phase transitions ending at a second order phase
transition in an extended bare parameter space.Comment: 7 pages, 7 figures, uses revtex, Eqs. 15-17 corrected, minor change
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