Four-loop contributions to long-distance quantities in the two-dimensional nonlinear sigma-model on a square lattice: revised numerical estimates

We give the correct analytic expression of a finite integral appearing in the four-loop computation of the renormalization-group functions for the two-dimensional nonlinear sigma-model on the square lattice with standard action, explaining the origin of a numerical discrepancy. We revise the numerical expressions of Caracciolo and Pelissetto for the perturbative corrections of the susceptibility and of the correlation length. For the values used in Monte Carlo simulations, N=3, 4, 8, the second perturbative correction coefficient of the correlation length varies by 3%, 4%, 3% respectively. Other quantities vary similarly.Comment: 2 pages, Revtex, no figure

The critical region of strong-coupling lattice QCD in different large-N limits

We study the critical behavior at nonzero temperature phase transitions of an effective Hamiltonian derived from lattice QCD in the strong-coupling expansion. Following studies of related quantum spin systems that have a similar Hamiltonian, we show that for large $N_c$ and fixed $g^2N_c$, mean field scaling is not expected, and that the critical region has a finite width at $N_c=\infty$. A different behavior rises for $N_f\to \infty$ and fixed $N_c$ and $g^2/N_f$, which we study in two spatial dimensions and for $N_c=1$. We find that the width of the critical region is suppressed by $1/N_f^p$ with $p=1/2$, and argue that a generalization to $N_c>1$ and to three dimensions will change this only in detail (e.g. the value of $p>0$), but not in principle. We conclude by stating under what conditions this suppression is expected, and remark on possible realizations of this phenomenon in lattice gauge theories in the continuum.Comment: 24 pages, 6 figures. New version includes: a more extensive discussion of strong-coupling expansions and their region of validity. Accordingly I have reworded the descriptions of the investigated limits. Removed typos and misprint

The W1+∞W_{1 + \infty } effective theory of the Calogero- Sutherland model and Luttinger systems.

We construct the effective field theory of the Calogero-Sutherland model in the thermodynamic limit of large number of particles $N$. It is given by a \winf conformal field theory (with central charge $c=1$) that describes {\it exactly} the spatial density fluctuations arising from the low-energy excitations about the Fermi surface. Our approach does not rely on the integrable character of the model, and indicates how to extend previous results to any order in powers of $1/N$. Moreover, the same effective theory can also be used to describe an entire universality class of $(1+1)$-dimensional fermionic systems beyond the Calogero-Sutherland model, that we identify with the class of {\it chiral Luttinger systems}. We also explain how a systematic bosonization procedure can be performed using the \winf generators, and propose this algebraic approach to {\it classify} low-dimensional non-relativistic fermionic systems, given that all representations of \winf are known. This approach has the appeal of being mathematically complete and physically intuitive, encoding the picture suggested by Luttinger's theorem.Comment: 13 pages, plain LaTeX, no figures

Lattice energy-momentum tensor with Symanzik improved actions

We define the energy-momentum tensor on lattice for the $\lambda \phi^4$ and for the nonlinear $\sigma$-model Symanzik tree-improved actions, using Ward identities or an explicit matching procedure. The resulting operators give the correct one loop scale anomaly, and in the case of the sigma model they can have applications in Monte Carlo simulations.Comment: Self extracting archive fil

The two-phase issue in the O(n) non-linear σ\sigma-model: A Monte Carlo study

We have performed a high statistics Monte Carlo simulation to investigate whether the two-dimensional O(n) non-linear sigma models are asymptotically free or they show a Kosterlitz- Thouless-like phase transition. We have calculated the mass gap and the magnetic susceptibility in the O(8) model with standard action and the O(3) model with Symanzik action. Our results for O(8) support the asymptotic freedom scenario.Comment: 3 pgs. espcrc2.sty included. Talk presented at LATTICE96(other models

Integration policies in modern age of migrations

During last century, especially since the late ‘70s, there was a drastic increase in the level of legal and clandestine immigration into the European Union, to which Community institutions have provided with an inadequate answer. Analyzing integration models and their application can one work a comparison between theoretical formulations and practical confirmations, especially about long term effects of the lack of a structural program aimed at regulating in a forward-looking manner the migration phenomena, which is intrinsic in human nature. The aim of this paper is to offer an overview about integration models application to the current situation, characterized by the conjunction of an increase in migratory fluxes and the global economic and financial crisis, in a Europe more and more concerned about the potential implications for internal security, but still far from the adoption of an agreed roadmap of concrete measures. Through a comparison of the systems implemented in some States, there will be a special focus to the model “of the emergency” that characterizes Italy, revealing how inadequate it is in a long term reception perspective, that is inevitable due to methods and motives correlated to what could be called a new age of migrations. Thereby, in conclusion, will be offered some interesting train of thought on regulation perspectives for achieving the harmonization of the social framework, in the spirit of a more acceptable reception, according to contemporary demands

Universality Class of O(N)O(N) Models

We point out that existing numerical data on the correlation length and magnetic susceptibility suggest that the two dimensional $O(3)$ model with standard action has critical exponent $\eta=1/4$, which is inconsistent with asymptotic freedom. This value of $\eta$ is also different from the one of the Wess-Zumino-Novikov-Witten model that is supposed to correspond to the $O(3)$ model at $\theta=\pi$.Comment: 8 pages, with 3 figures included, postscript. An error concerning the errors has been correcte

Gauged O(n) spin models in one dimension

We consider a gauged O(n) spin model, n >= 2, in one dimension which contains both the pure O(n) and RP(n-1) models and which interpolates between them. We show that this model is equivalent to the non-interacting sum of the O(n) and Ising models. We derive the mass spectrum that scales in the continuum limit, and demonstrate that there are two universality classes, one of which contains the O(n) and RP(n-1) models and the other which has a tuneable parameter but which is degenerate in the sense that it arises from the direct sum of the O(n) and Ising models.Comment: 9 pages, no figures, LaTeX sourc

Right to Dignity in Contemporary New Humanism

The evolution of national and international regulation outlined, especially in the last few decades, a number of legal figures that, as a result of an universal recognition, raises to human rights. Stands out from all the Right to Human Dignity, which is configured as inclusive of all cases so far spread considered, with a quid pluris constituted by its meaningful correlation to the very essence of human being: everyone deserves a dignified existence. Through the legal experiences in various States since the birth of modern codifications, we can assume how the concept of dignity is strictly related to that and the meaning concept of Persona. The present paper is founded on this basis, it concerns the adaptation of the concept of dignity in a changing global background where, at times, seems to be overshadowed