1,990 research outputs found
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 and fixed , mean
field scaling is not expected, and that the critical region has a finite width
at . A different behavior rises for and fixed
and , which we study in two spatial dimensions and for . We
find that the width of the critical region is suppressed by with
, and argue that a generalization to and to three dimensions
will change this only in detail (e.g. the value of ), 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 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 . It is given by a
\winf conformal field theory (with central charge ) 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 . Moreover, the same effective theory can also
be used to describe an entire universality class of -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 and
for the nonlinear -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
Integration policies in modern age of migrations
During last century, especially since the late â70s, 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 âof the emergencyâ 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
The two-phase issue in the O(n) non-linear -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
Universality Class of Models
We point out that existing numerical data on the correlation length and
magnetic susceptibility suggest that the two dimensional model with
standard action has critical exponent , which is inconsistent with
asymptotic freedom. This value of is also different from the one of the
Wess-Zumino-Novikov-Witten model that is supposed to correspond to the
model at .Comment: 8 pages, with 3 figures included, postscript. An error concerning the
errors has been correcte
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
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
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