Subdynamics of relevant observables: a field theoretical approach

An approach to the description of subdynamics inside non-relativistic quantum field theory is presented, in which the notions of relevant observable, time scale and complete positivity of the time evolution are stressed. A scattering theory derivation of the subdynamics of a microsystem interacting through collisions with a macrosystem is given, leading to a master-equation expressed in terms of the operator-valued dynamic structure factor, a two-point correlation function which compactly takes the statistical mechanics properties of the macrosystem into account. For the case of a free quantum gas the dynamic structure factor can be exactly calculated and in the long wavelength limit a Fokker-Planck equation for the description of quantum dissipation and in particular quantum Brownian motion is obtained, where peculiar corrections due to quantum statistics can be put into evidence.Comment: 28 pages, latex, no figure

Subdynamics as a mechanism for objective description

The relationship between microsystems and macrosystems is considered in the context of quantum field formulation of statistical mechanics: it is argued that problems on foundations of quantum mechanics can be solved relying on this relationship. This discussion requires some improvement of non-equilibrium statistical mechanics that is briefly presented.Comment: latex, 15 pages. Paper submitted to Proc. Conference "Mysteries, Puzzles And Paradoxes In Quantum Mechanics, Workshop on Entanglement And Decoherence, Palazzo Feltrinelli, Gargnano, Garda Lake, Italy, 20-25 September, 199

Unified treatment of the total angular momentum of single photons via generalized quantum observables

In this paper we provide a consistent framework to address the notorious decomposition of the single-photon total angular momentum (TAM) into a spin (SAM) and an orbital (OAM) component. In particular, we find that the canonical SAM and OAM, generators of internal and spatial rotations respectively in the space of physical states, are mutually compatible but unsharp quantum observables, therefore POVM (Positive Operator-Valued Measures) describe their joint measurements. On the other hand, a non-canonical SAM and OAM can be constructed that is mutually incompatible but represent sharp quantum observables, thus PVM (Projector-Valued Measurements), reflecting their consistency with the transversality condition characterizing singlephoton wavefunctions. We discuss the implementations on joint measurements for both decompositions and provide an explicit calculation of all these quantities for circularly polarized Gaussian single-photon states.Comment: 10 + 3 pages, 1 figur

Incoherent dynamics in neutron-matter interaction

Coherent and incoherent neutron-matter interaction is studied inside a recently introduced approach to subdynamics of a macrosystem. The equation describing the interaction is of the Lindblad type and using the Fermi pseudopotential we show that the commutator term is an optical potential leading to well-known relations in neutron optics. The other terms, usually ignored in optical descriptions and linked to the dynamic structure function of the medium, give an incoherent contribution to the dynamics, which keeps diffuse scattering and attenuation of the coherent beam into account, thus warranting fulfilment of the optical theorem. The relevance of this analysis to experiments in neutron interferometry is briefly discussed.Comment: 15 pages, revtex, no figures, to appear in Phys. Rev.

Quantum theory: the role of microsystems and macrosystems

We stress the notion of statistical experiment, which is mandatory for quantum mechanics, and recall Ludwig's foundation of quantum mechanics, which provides the most general framework to deal with statistical experiments giving evidence for particles. In this approach particles appear as interaction carriers between preparation and registration apparatuses. We further briefly point out the more modern and versatile formalism of quantum theory, stressing the relevance of probabilistic concepts in its formulation. At last we discuss the role of macrosystems, focusing on quantum field theory for their description and introducing for them objective state parameters.Comment: 12 pages. For special issue of J.Phys.A, "The Quantum Universe", on the occasion of 70th birthday of Professor Giancarlo Ghirard

Antología del pensamiento crítico venezolano contemporáneo

La presente Antología del pensamiento crítico venezolano contemporáneo se propone reflejar el conjunto de preocupaciones, temáticas, posiciones y propuestas que en los últimos cincuenta años han caracterizado el pensamiento crítico sobre la sociedad y sus determinaciones políticas y culturales. Se pretende presentar un panorama histórico-analítico de las inquietudes dominantes a través de sus referentes más relevantes, quienes centraron la comprensión y discusión de las realidades sociales de Venezuela en el contexto latinoamericano, y desarrollaron propuestas para su transformación. El enfoque general para la selección de las obras y autores/as partió de considerar que cada uno/a de ellos/as testimonia momentos de la reflexión social venezolana al servicio de una voluntad de cambio social, proponen una crítica radical del orden imperante y plantean posibilidades y vías para una superación de las relaciones de explotación y coloniaje existentes. En particular, la selección de textos trata de rescatar el continuo-discontinuo de la tradición del pensamiento antisistémico, con racionalidad rebelde, incorformista y subversiva. Con esta perspectiva se presenta una producción intelectual constructora de un pensamiento social que se hace cargo de la explicación de la realidad concreta, uniendo las dimensiones del conocimiento, la política y la ética, potenciadas en el contexto de un compromiso político que busca favorecer el cambio social. En suma; la producción de conocimiento recogida en esta compilación se ubica en el espacio del pensamiento transformador y comprometido