Correlation functions in the factorization approach of nonextensive quantum statistics

We study the long range behavior of a gas whose partition function depends on a parameter q and it has been claimed to be a good approximation to the partition function proposed in the formulation of nonextensive statistical mechanics. We compare our results, at large temperatures and at the critical point, with the case of Boltzmann-Gibbs thermodynamics for the case of a Bose-Einstein gas. In particular, we find that for all temperatures the long range correlations in a Bose gas decrease when the value of q departs from the standard value q=1.Comment: revtex file, 10 pages, two eps style figures, packaged as a single tar.gz fil

Quark Model and multiquark system

The discovery of many particles, especially in the 50's, when the firsts accelerators appeared, caused the searching for a model that would describe in a simple form the whole of known particles. The Quark Model, based in the mathematical structures of group theory, provided in the beginning of the 60's a simplified description of hadronic matter already known, proposing that three particles, called quarks, would originate all the observed hadrons. This model was able to preview the existence of particles that were later detected, confirming its consistency. Extensions of the Quark Model were made in the beginning of the 70's, focusing in describing observed particles that were excited states of the fundamental particles and others that presented new quantum numbers (flavors). Recently, exotic states as tetraquarks and pentaquarks types, also called multiquarks systems, previewed by the model, were observed, what renewed the interest in the way as quarks are confined inside the hadrons. In this article we present a review of the Quark Model and a discussion on the new exotic states.Comment: In Portugues

Metamodelling Messages Conveyed in Five Statistical Mechanical Textbooks from 1936 to 2001

Modelling is a significant aspect of doing physics and it is important how this activity is taught. This paper focuses on the explicit or implicit messages about modelling conveyed to the student in the treatments of phase transitions in statistical mechanics textbooks at beginning graduate level. Five textbooks from the 1930s to the present are analysed with respect to their messages about the following issues: What is a good model? What is the purpose of modelling? What does it mean to understand a natural phenomenon? It is argued that these texts give the student quite different perceptions of these issues and thus what of it means to do physics