The behavior of the sextic coupling for the scalar field at the intermediate and strong coupling regime

We study the behavior of the renormalized sextic coupling at the intermediate and strong coupling regime for the $\phi^4$ theory defined in $d=2$-dimension. We found a good agreement with the results obtained by the field-theoretical renormalization-group in the Ising limit. In this work we use the lattice regularization method.Comment: 10 pages, 1 figure. To be published in Modern Physics Letters

Scalar Field Theory at Finite Temperature in D=2+1

We discuss the phi(6) theory defined in D = 2 + 1-dimensional space-time and assume that the system is in equilibrium with a thermal bath at temperature beta(-1). We use the 1/N expansion and the method of composite operator (CJT) for summing a large set of Feynman graphs. We demonstrate explicitly the Coleman-Mermin-Wagner theorem at finite temperature

Les Magasins généraux : de spot à vandales à spot publicitaire ?

Cet article prend comme cas d’étude la réhabilitation des Magasins généraux à Pantin, ville limitrophe à la capitale française et appartenant au département de la Seine-Saint-Denis (93). Il s’attarde sur le processus de transformation urbaine du bâtiment, de son état de friche à celui de spot du graffiti et du street art pour devenir ensuite un centre culturel géré par l’agence publicitaire BETC Paris. Lors de ce processus de transformation, le graffiti et le street art sont mobilisés comme des outils de valorisation symbolique du territoire. Ce faisant, ils permettent aussi de légitimer la création du lieu institutionnel et la mise en place à sa tête d’un acteur original qui s’inscrit ainsi dans les processus de production et de médiation culturelles et urbaines à l’échelle métropolitaine. En utilisant l’art comme outil de développement économique, l’agence publicitaire aussi bien que les acteurs territoriaux publics favorise l’émergence du modèle socio-économique de la ville créative.This paper focuses on a study case of the renovation of an industrial building, the Magasins généraux in Pantin, a suburban city bordering the French capital and belonging to the Seine-Saint-Denis department (93). Due to the deindustrialisation process, the industrial activites in the building were shut down in 2001 and it became an industrial wasteland. From 2004, it was invested by graffiti and street artists to then be transformed in what it is today : a cultural centre managed by the advertising company BETC Paris. During the transformation, graffiti and street art were used as tools both to promote the territory and the agency settling in the building. By their presence in and invasion of the building, they gave it a symbolical value. Such value has been turned into a strategic mercantile one to legitimate the implantation of this original actor on the metropolis scale and to promote a socio-economic model based on the concept of the creative city

Sensitivity function and entropy increase rates for z-logistic map family at the edge of chaos

It is well known that, for chaotic systems, the production of relevant entropy (Boltzmann-Gibbs) is always linear and the system has strong (exponential) sensitivity to initial conditions. In recent years, various numerical results indicate that basically the same type of behavior emerges at the edge of chaos if a specific generalization of the entropy and the exponential are used. In this work, we contribute to this scenario by numerically analysing some generalized nonextensive entropies and their related exponential definitions using $z$-logistic map family. We also corroborate our findings by testing them at accumulation points of different cycles.Comment: 9 pages, 2 fig

q-Generalization of the inverse Fourier transform

A wide class of physical distributions appears to follow the q-Gaussian form, which plays the role of attractor according to a Central Limit Theorem generalized in the presence of specific correlations between the relevant random variables. In the realm of this theorem, a q-generalized Fourier transform plays an important role. We introduce here a method which univocally determines a distribution from the knowledge of its q-Fourier transform and some supplementary information. This procedure involves a recently q-generalized Dirac delta and the class of functions on which it acts. The present method conveniently extends the inverse of the standard Fourier transform, and is therefore expected to be very useful in the study of many complex systems.Comment: 6 pages, 3 figures. To appear in Physics Letters

Constraining nonextensive statistics with plasma oscillation data

We discuss experimental constraints on the free parameter of the nonextensive kinetic theory from measurements of the thermal dispersion relation in a collisionless plasma. For electrostatic plane-wave propagation, we show through a statistical analysis that a good agreement between theory and experiment is possible if the allowed values of the $q$-parameter are restricted by $q=0.77 \pm 0.03$ at 95% confidence level (or equivalently, $2-q = 1.23$, in the largely adopted convention for the entropy index $q$). Such a result rules out (by a large statistical margin) the standard Bohm-Gross dispersion relation which is derived assuming that the stationary Maxwellian distribution ($q=1$) is the unperturbed solution.Comment: 4 pages, 2 figure

The thermal coupling constant and the gap equation in the λϕD4\lambda\phi^{4}_{D} model

By the concurrent use of two different resummation methods, the composite operator formalism and the Dyson-Schwinger equation, we re-examinate the behavior at finite temperature of the O(N)-symmetric $\lambda\phi^{4}$ model in a generic D-dimensional Euclidean space. In the cases D=3 and D=4, an analysis of the thermal behavior of the renormalized squared mass and coupling constant are done for all temperatures. It results that the thermal renormalized squared mass is positive and increases monotonically with the temperature. The behavior of the thermal coupling constant is quite different in odd or even dimensional space. In D=3, the thermal coupling constant decreases up to a minimum value diferent from zero and then grows up monotonically as the temperature increases. In the case D=4, it is found that the thermal renormalized coupling constant tends in the high temperature limit to a constant asymptotic value. Also for general D-dimensional Euclidean space, we are able to obtain a formula for the critical temperature of the second order phase transition. This formula agrees with previous known values at D=3 and D=4.Comment: 23 pages, 4 figure

A Shannon-Tsallis transformation

We determine a general link between two different solutions of the MaxEnt variational problem, namely, the ones that correspond to using either Shannon's or Tsallis' entropies in the concomitant variational problem. It is shown that the two variations lead to equivalent solutions that take different appearances but contain the same information. These solutions are linked by our transformation

Dimensional Reduction of Fermions in Brane Worlds of the Gross-Neveu Model

We study the dimensional reduction of fermions, both in the symmetric and in the broken phase of the 3-d Gross-Neveu model at large N. In particular, in the broken phase we construct an exact solution for a stable brane world consisting of a domain wall and an anti-wall. A left-handed 2-d fermion localized on the domain wall and a right-handed fermion localized on the anti-wall communicate with each other through the 3-d bulk. In this way they are bound together to form a Dirac fermion of mass m. As a consequence of asymptotic freedom of the 2-d Gross-Neveu model, the 2-d correlation length \xi = 1/m increases exponentially with the brane separation. Hence, from the low-energy point of view of a 2-d observer, the separation of the branes appears very small and the world becomes indistinguishable from a 2-d space-time. Our toy model provides a mechanism for brane stabilization: branes made of fermions may be stable due to their baryon asymmetry. Ironically, our brane world is stable only if it has an extreme baryon asymmetry with all states in this ``world'' being completely filled.Comment: 26 pages, 7 figure