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F. Di Renzo

Publications and source records attributed to F. Di Renzo.

65 records · Page 4Linked to original sources
arXiv1999

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.

hep-lat↗
arXiv1998

Search for 1/p^2 Corrections to the Running QCD Coupling

We investigate the occurrence of power terms in the running QCD coupling by analysing non-perturbative measurements of alpha_s (p) at low momenta obtained from the lattice three-gluon vertex. Our exploratory study provides some evidence for power contributions to alpha_s (p) proportional to 1/p^2. Possible implications for physical observables are discussed.

hep-ph↗
arXiv1998

Search for Lambda^2/p^2 corrections to the QCD running coupling

We investigate the occurrence of power terms $(Lambda^2/p^2$ in the running QCD coupling by analysing non-perturbative measurements of $α_s(p)$ at quite low momenta obtained from the lattice three-gluon vertex. Our study provides some evidence for such a contribution. The phenomenological implications of such a presence are reviewed.

hep-lat↗
arXiv1998

The running QCD coupling in the pre-asymptotic region

We study deviations from the perturbative asymptotic behaviour in the running QCD coupling by analysing non-perturbative measurements of alpha_s (p) at low momenta as obtained from the lattice three-gluon vertex. Our exploratory study provides some evidence for power corrections to the perturbative running proportional to 1/p^2.

hep-ph↗
arXiv1998

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.

hep-lat↗
arXiv1997

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.

hep-lat↗
arXiv1997

Developments and new applications of numerical stochastic perturbation theory

A review of new developments in numerical stochastic perturbation theory (NSPT) is presented. In particular, the status of the extension of the method to gauge fixed lattice QCD is reviewed and a first application to compact (scalar) QED is presented. Lacking still a general proof of the convergence of the underlying stochastic processes, a self-consistent method for testing the results is discussed.

hep-lat↗
arXiv1997

Lambda^2-contribution to the condensate in lattice gauge theory

We present some evidence that in Lattice Gauge Theory the condensate contains a non-perturbative contribution proportional to $Λ^2$, the square of the physical scale. This result is based on an analysis of the Wilson loop plaquette expectation from Monte Carlo simulations and its perturbative expansion computed to eight loops. The analysis is not fully conclusive since the calculations are done on a finite lattice and one needs an extrapolation to infinite lattice. It has been recently suggested that in the gluon condensate a $Λ^2$-contribution could be present coming from the large momentum behaviour of the running coupling and not connected to operator product expansion.

hep-ph↗
arXiv1995

RENORMALONS FROM EIGHT LOOP EXPANSION OF THE GLUON CONDENSATE IN LATTICE GAUGE THEORY,

We use a numerical method to obtain the weak coupling perturbative coefficients of local operators with lattice regularization. Such a method allows us to extend the perturbative expansions obtained so far by analytical Feynman diagrams calculations. In SU(3) lattice gauge theory in four dimensions we compute the first eight coefficients of the expectation value of the Wilson loop on the elementary plaquette which is related to the gluon condensate. The computed eight coefficients grow with the order much faster than predicted by the presence of the infrared renormalon associated to the dimension of the gluon condensate. However the renormalon behaviour for large order is quite well reproduced if one considers the expansion coefficients in a new coupling related to the lattice coupling by large perturbative corrections. This is expected since the lattice and continuum Lambda scales differ by almost two orders of magnitude.

hep-th↗
arXiv1994

Four Loop Result in $SU(3)$ Lattice Gauge Theory by a Stochastic Method: Lattice Correction to the Condensate

We describe a stochastic technique which allows one to compute numerically the coefficients of the weak coupling perturbative expansion of any observable in Lattice Gauge Theory. The idea is to insert the exponential representation of the link variables $U_μ(x) \to \exp\{A_μ(x)/\sqrtβ\}$ into the Langevin algorithm and the observables and to perform the expansion in β^{-1/2}. The Langevin algorithm is converted into an infinite hierarchy of maps which can be exactly truncated at any order. We give the result for the simple plaquette of SU(3) up to fourth loop order (β^{-4}) which extends by one loop the previously known series.

hep-lat↗