1,756 research outputs found
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
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
One-dimensional QCD in thimble regularization
QCD in 0+1 dimensions is numerically solved via thimble regularization. In
the context of this toy model, a general formalism is presented for SU(N)
theories. The sign problem that the theory displays is a genuine one, stemming
from a (quark) chemical potential. Three stationary points are present in the
original (real) domain of integration, so that contributions from all the
thimbles associated to them are to be taken into account: we show how
semiclassical computations can provide hints on the regions of parameter space
where this is absolutely crucial. Known analytical results for the chiral
condensate and the Polyakov loop are correctly reproduced: this is in
particular trivial at high values of the number of flavors N_f. In this regime
we notice that the single thimble dominance scenario takes place (the dominant
thimble is the one associated to the identity). At low values of N_f
computations can be more difficult. It is important to stress that this is not
at all a consequence of the original sign problem (not even via the residual
phase). The latter is always under control, while accidental, delicate
cancelations of contributions coming from different thimbles can be in place in
(restricted) regions of the parameter space.Comment: 20 pages, 5 figures (many more pdf files) (one reference added
Power corrections and perturbative coupling from lattice gauge thoeries
From the analysis of the perturbative expansion of the lattice regularized
gluon condensate, toghether with MC data, we present evidence of OPE-unexpected
dim-2 power corrections in the scaling behaviour of the Wilson loop. These can
be interpreted as an indication that in lattice gauge theories the running
coupling at large momentum contains contributions of order Q^2.Comment: 3 pages, 2 figures. Talk given at the Lattice97 conference,
Edinburgh, U
New issues for Numerical Stochastic Perturbation Theory
First attempts in the application of Numerical Stochastic Perturbation Theory
(NSPT) to the problem of pushing one loop further the computation of SU(3)
(SU(2)) pertubative beta function (in different schemes) are reviewed and the
relevance of such a computation is discussed. Other issues include the proposal
of a different strategy for gauge-fixed NSPT computations in lattice QCD.Comment: 3 pages, Latex, LATTICE98(algorithms
B Physics on the Lattice: , , , , mixing, \fb and all that
We present a short review of our most recent high statistics lattice
determinations in the HQET of the following important parameters in B physics:
the B--meson binding energy, and the kinetic energy of the
b quark in the B meson, , which due to the presence of power
divergences require a non--perturbative renormalization to be defined; the
running mass of the b quark,
; the -- mass splitting, whose
value in the HQET is determined by the matrix element of the chromo--magnetic
operator between B meson states, ; the B parameter of the
-- mixing, , and the decay constant of the B meson,
. All these quantities have been computed using a sample of gauge
field configurations on a lattice at . For
and , we obtain our
estimates by combining results from three independent lattice simulations at
, and on the same volume.Comment: 3 latex pages, uses espcrc2.sty (included). Talk presented at
LATTICE96(heavy quarks
An efficient flamelet progress-variable method for modeling non-premixed flames in weak electric fields
Combustion stabilization and enhancement of the flammability limits are
mandatory objectives to improve nowadays combustion chambers. At this purpose,
the use of an electric field in the flame region provides a solution which is,
at the same time, easy to implement and effective to modify the flame
structure. The present work describes an efficient flamelet progress-variable
approach developed to model the fluid dynamics of flames immersed in an
electric field. The main feature of this model is that it can use complex
ionization mechanisms without increasing the computational cost of the
simulation. The model is based on the assumption that the combustion process is
not directly influenced by the electric field and has been tested using two
chemi-ionization mechanisms of different complexity in order to examine its
behavior with and without the presence of heavy anions in the mixture. Using a
one- and two-dimensional numerical test cases, the present approach has been
able to reproduce all the major aspects encountered when a flame is subject to
an imposed electric field and the main effects of the different chemical
mechanisms. Moreover, the proposed model is shown to produce a large reduction
in the computational cost, being able to shorten the time needed to perform a
simulation up to 40 times.Comment: 26 pages, 13 figures, paper accepted for publication on Computers and
Fluid
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