2,458 research outputs found
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
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
The Lattice Free Energy with Overlap Fermions: A Two-Loop Result
We calculate the 2-loop partition function of QCD on the lattice, using the
Wilson formulation for gluons and the overlap-Dirac operator for fermions.
Direct by-products of our result are the 2-loop free energy and average
plaquette. Our calculation serves also as a prototype for further higher loop
calculations in the overlap formalism. We present our results as a function of
a free parameter entering the overlap action; the dependence on the
number of colors and fermionic flavors is shown explicitly.Comment: 10 pages, 5 figures. Final version to appear in Physical Review D. A
missing overall factor was inserted in Eq. 12; it affects also Eq. 1
Quantum field theories on the Lefschetz thimble
In these proceedings, we summarize the Lefschetz thimble approach to the sign
problem of Quantum Field Theories. In particular, we review its motivations,
and we summarize the results of the application of two different algorithms to
two test models.Comment: contributions to 31st International Symposium on Lattice Field Theory
- LATTICE 2013, July 29 - August 3, 2013, Mainz, Germany and QCD-TNT-III, 2-6
September, 2013, European Centre for Theoretical Studies in Nuclear Physics
and Related Areas (ECT*), Villazzano, Trento (Italy
Four loop stochastic perturbation theory in 3d SU(3)
Dimensional reduction is a key issue in finite temperature field theory. For
example, when following the QCD Free Energy from low to high scales across the
critical temperature, ultrasoft degrees of freedom can be captured by a 3d
SU(3) pure gauge theory. For such a theory a complete perturbative matching
requires four loop computations, which we undertook by means of Numerical
Stochastic Perturbation Theory. We report on the computation of the pure gauge
plaquette in 3d, and in particular on the extraction of the logarithmic
divergence at order g^8, which had already been computed in the continuum.Comment: 3 pages, 2 figure, Lattice2003(nonzero
3-d Lattice QCD Free Energy to Four Loops
We compute the expansion of the 3-d Lattice QCD free energy to four loop
order by means of Numerical Stochastic Perturbation Theory. The first and
second order are already known and are correctly reproduced. The third and
fourth order coefficients are new results. The known logarithmic divergence in
the fourth order is correctly identified. We comment on the relevance of our
computation in the context of dimensionally reduced finite temperature QCD.Comment: 8 pages, 3 figures, latex typeset with JHEP3.cl
Development of improved cadmium sulfide solar cells Final report, 18 Feb. 1969 - 18 Mar. 1970
Development of improved cadmium sulfide solar cell
Two-point functions of quenched lattice QCD in Numerical Stochastic Perturbation Theory
We summarize the higher-loop perturbative computation of the ghost and gluon
propagators in SU(3) Lattice Gauge Theory. Our final aim is to compare with
results from lattice simulations in order to expose the genuinely
non-perturbative content of the latter. By means of Numerical Stochastic
Perturbation Theory we compute the ghost and gluon propagators in Landau gauge
up to three and four loops. We present results in the infinite volume and limits, based on a general fitting strategy.Comment: 3 pages, 5 figures, talk at conference QCHS-IX, Madrid 201
Two-point functions of quenched lattice QCD in Numerical Stochastic Perturbation Theory. (I) The ghost propagator in Landau gauge
This is the first of a series of two papers on the perturbative computation
of the ghost and gluon propagators in SU(3) Lattice Gauge Theory. Our final aim
is to eventually compare with results from lattice simulations in order to
enlight the genuinely non-perturbative content of the latter. By means of
Numerical Stochastic Perturbation Theory we compute the ghost propagator in
Landau gauge up to three loops. We present results in the infinite volume and
limits, based on a general strategy that we discuss in detail.Comment: 27 pages, 11 figure
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