arXiv subjects

Attilio Cucchieri

Publications and source records attributed to Attilio Cucchieri.

At least 73 records · Page 4Linked to original sources

arXiv2003

Propagators and running coupling from SU(2) lattice gauge theory

We perform numerical studies of the running coupling constant alpha_R(p^2) and of the gluon and ghost propagators for pure SU(2) lattice gauge theory in the minimal Landau gauge. Different definitions of the gauge fields and different gauge-fixing procedures are used respectively for gaining better control over the approach to the continuum limit and for a better understanding of Gribov-copy effects. We find that the ghost-ghost-gluon-vertex renormalization constant is finite in the continuum limit, confirming earlier results by all-order perturbation theory. In the low momentum regime, the gluon form factor is suppressed while the ghost form factor is divergent. Correspondingly, the ghost propagator diverges faster than 1/p^2 and the gluon propagator appears to be finite. Precision data for the running coupling alpha_R(p^2) are obtained. These data are consistent with an IR fixed point given by lim_{p \to 0} alpha_R(p^2) = 5(1).

hep-lat↗

arXiv2003

Parallel implementation of a lattice-gauge-theory code: studying quark confinement on PC clusters

We consider the implementation of a parallel Monte Carlo code for high-performance simulations on PC clusters with MPI. We carry out tests of speedup and efficiency. The code is used for numerical simulations of pure SU(2) lattice gauge theory at very large lattice volumes, in order to study the infrared behavior of gluon and ghost propagators. This problem is directly related to the confinement of quarks and gluons in the physics of strong interactions.

hep-lat↗

arXiv2003

Critical Slowing-Down in SU(2) Landau-Gauge-Fixing Algorithms at beta = infinity

We evaluate numerically and analytically the dynamic critical exponent $z$ for five gauge-fixing algorithms in SU(2) lattice Landau-gauge theory by considering the case $β= \infty$. Numerical data are obtained in two, three and four dimensions. Results are in agreement with those obtained previously at finite $β$ in two dimensions. The theoretical analysis, valid for any dimension $d$, helps us clarify the tuning of these algorithms. We also study generalizations of the overrelaxation algorithm and of the stochastic overrelaxation algorithm and verify that we cannot have a dynamic critical exponent $z$ smaller than 1 with these local algorithms. Finally, the analytic approach is applied to the so-called $λ$-gauges, again at $β= \infty$, and verified numerically for the two-dimensional case.

hep-lat↗

arXiv2003

SU(2) Landau gluon propagator on a 140^3 lattice

We present a numerical study of the gluon propagator in lattice Landau gauge for three-dimensional pure-SU(2) lattice gauge theory at couplings beta = 4.2, 5.0, 6.0 and for lattice volumes V = 40^3, 80^3, 140^3. In the limit of large V we observe a decreasing gluon propagator for momenta smaller than p_{dec} = 350^{+ 100}_{- 50} MeV. Data are well fitted by Gribov-like formulae and seem to indicate an infra-red critical exponent kappa slightly above 0.6, in agreement with recent analytic results.

hep-lat↗

arXiv2002

Running coupling constant and propagators in SU(2) Landau gauge

We present a numerical study of the running coupling constant and of the gluon and ghost propagators in minimal Landau gauge. Simulations are done in pure SU(2) lattice gauge theory for several values of beta and lattice sizes. We use two different lattice setups.

hep-lat↗

arXiv2002

Lattice simulations for the running coupling constant of QCD

The strong coupling constant alpha_s(mu_0), taken at a fixed reference scale mu_0, is the single free parameter of QCD and should be known to the highest available precision. The value of alpha_s should also be determined with good accuracy over as large a range of scales as possible, in order to reveal potential anomalous running in the strength of the strong interaction. Lattice QCD is now able to calculate alpha_s with accuracy comparable to or better than experiment. We review the status of such lattice calculations in quenched and full QCD.

hep-lat↗

arXiv2002

Gluon propagator and confinement scenario in Coulomb gauge

We present numerical results in SU(2) lattice gauge theory for the instantaneous part of the gluon propagator in Coulomb gauge D_{44, inst} = V_{coul}(R) δ(t). Data are taken on lattice volumes 24^4 and 28^4 for 7 values of beta in the interval $2.2 \leq beta \leq 2.8$. The data are confronted with the confinement scenario in Coulomb gauge. They are consistent with a linearly rising color-Coulomb potential V_{coul}(R).

hep-lat↗

arXiv2001

Fit to Gluon Propagator and Gribov Formula

We report a numerical study of SU(2) lattice gauge theory in the minimal Coulomb gauge at beta = 2.2 and 9 different volumes. After extrapolation to infinite volume, our fit agrees with a lattice discretization of Gribov's formula for the transverse equal-time would-be physical gluon propagator, that vanishes like |k| at k = 0, whereas the free equal-time propagator (2|k|)^{-1} diverges. Our fit lends reality to a confinement scenario in which the would-be physical gluons leave the physical spectrum while the long-range Coulomb force confines color.

hep-lat↗

arXiv2001

Confinement made simple in the Coulomb gauge

In Gribov's scenario in Coulomb gauge, confinement of color charge is due to a long-range instantaneous color-Coulomb potential V(R). This may be determined numerically from the instantaneous part of the gluon propagator D_{44, inst} = V(R) δ(t). Confinement of gluons is reflected in the vanishing at k = 0 of the equal-time three-dimensionally transverse would-be physical gluon propagator D^{tr}(k). We present exact analytic results on D_{44} and D^{tr} (which have also been investigated numerically, A. Cucchieri, T. Mendes, and D. Zwanziger, this conference), in particular the vanishing of D^{tr}(k) at k = 0, and the determination of the running coupling constant from x_0 g^2(k) = k^2 D_{44, inst}, where x_0 = 12N/(11N-2N_f).

hep-lat↗

arXiv2001

SU(2) Running Coupling Constant and Confinement in Minimal Coulomb and Landau Gauges

We present a numerical study of the space-space and time-time components of the gluon propagator at equal time in the minimal Coulomb gauge, and of the gluon and ghost propagators in the minimal Landau gauge. This work allows a non-perturbative evaluation of the running coupling constant and a numerical check of Gribov's confinement scenarios for these two gauges. Our simulations are done in pure SU(2) lattice gauge theory at $β= 2.2$. We consider several lattice volumes in order to control finite-volume effects and extrapolate our results to infinite lattice volume.

hep-lat↗

arXiv2001

Numerical Study of Gluon Propagator and Confinement Scenario in Minimal Coulomb Gauge

We present numerical results in SU(2) lattice gauge theory for the space-space and time-time components of the gluon propagator at equal time in the minimal Coulomb gauge. It is found that the equal-time would-be physical 3-dimensionally transverse gluon propagator $D^{tr}(\vec{k})$ vanishes at $\vec{k} = 0$ when extrapolated to infinite lattice volume, whereas the instantaneous color-Coulomb potential $D_{44}(\vec{k})$ is strongly enhanced at $\vec{k} = 0$. This has a natural interpretation in a confinement scenario in which the would-be physical gluons leave the physical spectrum while the long-range Coulomb force confines color. Gribov's formula $D^{tr}(\vec{k}) = (|\vec{k}|/2)[(\vec{k}^2)^2 + M^4]^{1/2}$ provides an excellent fit to our data for the 3-dimensionally transverse equal-time gluon propagator $D^{tr}(\vec{k})$ for relevant values of $\vec{k}$.

hep-lat↗

arXiv2001

Renormalization-group Calculation of Color-Coulomb Potential

We report here on the application of the perturbative renormalization-group to the Coulomb gauge in QCD. We use it to determine the high-momentum asymptotic form of the instantaneous color-Coulomb potential $V(\vec{k})$ and of the vacuum polarization $P(\vec{k}, k_4)$. These quantities are renormalization-group invariants, in the sense that they are independent of the renormalization scheme. A scheme-independent definition of the running coupling constant is provided by $\vec{k}^2 V(\vec{k}) = x_0 g^2(\vec{k}/Λ_{coul})$, and of $α_s \equiv {{g^2(\vec{k} / Λ_{coul})} \over {4π}}$, where $x_0 = {{12N} \over {11N - 2N_f}}$, and $Λ_{coul}$ is a finite QCD mass scale. We also show how to calculate the coefficients in the expansion of the invariant $β$-function $β(g) \equiv |\vec{k}| {{\partial g} \over{\partial |\vec{k}|}} = -(b_0 g^3 + b_1 g^5 +b_2 g^7 + ...)$, where all coefficients are scheme-independent.

hep-th↗

arXiv1999

Discretization effects and gauge independence for the electric and magnetic screening masses

We evaluate the electric and magnetic screening masses from the long-distance behavior of the (temporal and spatial) gluon correlation functions, for pure SU(2) gauge theory at finite temperature. In order to investigate the gauge dependence of the screening masses we consider seven different gauges. We also evaluate these masses using different definitions of the lattice gluon field, corresponding to discretization errors of different orders.

hep-lat↗

arXiv1999

The lattice gluon propagator into the next millennium

We evaluate numerically the momentum-space gluon propagator in the lattice Landau gauge, for three- and four-dimensional pure SU(2) lattice gauge theory. Although there are large finite-size effects, we always observe, in the limit of large lattice volumes, a gluon propagator decreasing in the infrared limit. This result can be interpreted in a straightforward way, by considering the proximity of the so-called first Gribov horizon in the infrared directions. We also consider the problem of discretization errors introduced by the lattice regularization, and their effect on the ultraviolet behavior of the gluon propagator.

hep-lat↗

arXiv1999

Infrared behavior of the gluon propagator in lattice Landau gauge: the three-dimensional case

We evaluate numerically the three-momentum-space gluon propagator in the lattice Landau gauge, for three-dimensional pure-SU(2) lattice gauge theory with periodic boundary conditions. Simulations are done for nine different values of the coupling $β$, from $β= 0$ (strong coupling) to $β= 6.0$ (in the scaling region), and for lattice sizes up to $V = 64^3$. In the limit of large lattice volume we observe, in all cases, a gluon propagator decreasing for momenta smaller than a constant value $p_{dec}$. From our data we estimate $p_{dec} \approx 350$ MeV. The result of a gluon propagator decreasing in the infrared limit has a straightforward interpretation as resulting from the proximity of the so-called first Gribov horizon in the infrared directions.

hep-lat↗

arXiv1999

Gauge fixing and gluon propagator in lambda-gauges

We discuss critical slowing-down of several gauge-fixing algorithms for the so-called lambda-gauges in the SU(2) case at zero temperature. For these gauges we also evaluate the gluon propagator using different definitions of the lattice gluon field, corresponding to discretization errors of different orders.

hep-lat↗

arXiv1998

Pseudo-Character Expansions for U(N)-Invariant Spin Models on CP^{N-1}

We define a set of orthogonal functions on the complex projective space CP^{N-1}, and compute their Clebsch-Gordan coefficients as well as a large class of 6-j symbols. We also provide all the needed formulae for the generation of high-temperature expansions for U(N)-invariant spin models defined on CP^{N-1}.

hep-lat↗

arXiv1998

Effects of Nonperturbative Improvement in Quenched Hadron Spectroscopy

We discuss a comparative analysis of unimproved and nonperturbatively improved quenched hadron spectroscopy, on a set of 104 gauge configurations, at beta=6.2. We also present here our results for meson decay constants, including the constants f_D and f_Ds in the charm-quark region.

hep-lat↗