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M. Campostrini

Publications and source records attributed to M. Campostrini.

29 records · Page 2Linked to original sources
arXiv1997

On the evaluation of universal non-perturbative constants in O(N) sigma models

We investigate the relation between on-shell and zero-momentum non-perturbative quantities entering the parametrization of the two-point Green's function of two-dimensional non-linear O(N) sigma models. We present accurate estimates of ratios of mass-scales and renormalization constants, obtained by an analysis of the strong-coupling expansion of the two-point Green's function. These ratios allow to connect exact known on-shell results with typical zero-momentum lattice evaluations. Our results are supported by the 1/N-expansion.

hep-lat↗
arXiv1995

Four-point renormalized coupling constant in O(N) models

The renormalized zero-momentum four-point coupling $g_r$ of $O(N)$-invariant scalar field theories in $d$ dimensions is studied by applying the $1/N$ expansion and strong coupling analysis. The $O(1/N)$ correction to the $β$-function and to the fixed point value $g_r^*$ are explictly computed. Strong coupling series for lattice non-linear $σ$ models are analyzed near criticality in $d=2$ and $d=3$ for several values of $N$ and the corresponding values of $g_r^*$ are extracted. Large-$N$ and strong coupling results are compared with each other, finding a good general agreement. For small $N$ the strong coupling analysis in 2-d gives the best determination of $g^*_r$ to date (or comparable for $N=2,3$ with the available Monte Carlo estimates), and in 3-d it is consistent with available $ϕ^4$ field theory results.

hep-lat↗
arXiv1995

Critical Behavior of Simplicial Chiral Models

The large-N saddle-point equations for the principal chiral models defined on a d-1 dimensional simplex are derived from the external field problem for unitary integrals. The saddle point equation are studied analytically and numerically in many relevant instances, including d=4 and $d\rightarrow\infty$, with special attention to the critical domain, which is found to correspond to $β_c=1/d$ for all d. Related models (chiral chains) are discussed and large-N solutions are analyzed.

hep-th↗
arXiv1995

Four-point renormalized coupling constant in O(N) models

The renormalized zero-momentum four-point coupling $g_r$ of O(N)-invariant scalar field theories in $d$ dimensions is studied by applying the 1/N expansion and strong coupling analysis. The O(1/N) correction to the $β$-function and to the fixed point value $g_r^*$ are explictly computed. Strong coupling series for lattice non-linear sigma models are analyzed near criticality in d=2 and d=3 for several values of $N$ and the corresponding values of $g_r^*$ are extracted. Large-N and strong coupling results are compared with each other, finding a good general agreement. For small N the strong coupling analysis in 2-d gives the best determination of $g^*_r$ to date (or comparable for N=2,3 with the available Monte Carlo estimates), and in 3-d it is consistent with available $ϕ^4$ field theory results.

hep-lat↗
arXiv1994

Strong coupling analysis of the large-N 2-d lattice chiral models

Two dimensional large-N chiral models on the square and honeycomb lattices are investigated by a strong coupling analysis. Strong coupling expansion turns out to be predictive for the evaluation of continuum physical quantities, to the point of showing asymptotic scaling. Indeed in the strong coupling region a quite large range of beta values exists where the fundamental mass agrees, within about 5% on the square lattice and about 10% on the honeycomb lattice, with the continuum predictions in the %%energy scheme.

hep-lat↗
arXiv1994

Large-N phase transition in lattice 2-d principal chiral models

We investigate the large-N critical behavior of 2-d lattice chiral models by Monte Carlo simulations of U(N) and SU(N) groups at large N. Numerical results confirm strong coupling analyses, i.e. the existence of a large-N second order phase transition at a finite $β_c$.

hep-lat↗
arXiv1994

Strong coupling expansion of chiral models

A general precedure is outlined for an algorithmic implementation of the strong coupling expansion of lattice chiral models on arbitrary lattices. A symbolic character expansion in terms of connected values of group integrals on skeleton diagrams may be obtained by a fully computerized approach.

hep-lat↗
arXiv1994

The spin content of the proton in quenched QCD

We present preliminary results on the proton spin structure function at zero momentum, in the quenched approximation. Our calculation makes use of a nonperturbative means of determining the multiplicative renormalization of the topological charge density.

hep-lat↗
arXiv1992

Three-Loop Results on the Lattice

We present some new three-loop results in lattice gauge theories, for the Free Energy and for the Topological Susceptibility. These results are an outcome of a scheme which we are developing (using a symbolic manipulation language), for the analytic computation of renormalization functions on the lattice.

hep-lat↗
arXiv1992

Topological susceptibility and string tension in the lattice CP(N) models

In the lattice CP(N) models we studied the problems related to the measure of the topological susceptibility and the string tension . We perfomed numerical simulations at N=4 and N=10. In order to test the universality, we adopted two different lattice formulations. Scaling and universality tests led to the conclusion that at N=10 the geometrical approach gives a good definition of lattice topological susceptibility. On the other hand, N=4 proved not to be large enough to suppress the unphysical configurations, called dislocations, contributing to the topological susceptibility. We obtained other determinations of the topological susceptibility by the field theoretical method, wich relies on a local definition of the lattice topological charge density, and the cooling method. They gave quite consistent results, showing scaling and universality. The large-N expansion predicts an exponential area law behavior for sufficiently large Wilson loops, which implies confinement, due to the dynamical matter fields and absence of the screening phenomenon. We determined the string tension, without finding evidence of screening effects.

hep-lat↗