Thermal behavior induced by vacuum polarization on causal horizons in comparison with the standard heat bath formalism

Modular theory of operator algebras and the associated KMS property are used to obtain a unified description for the thermal aspects of the standard heat bath situation and those caused by quantum vacuum fluctuations from localization. An algebraic variant of lightfront holography reveals that the vacuum polarization on wedge horizons is compressed into the lightray direction. Their absence in the transverse direction is the prerequisite to an area (generalized Bekenstein-) behavior of entropy-like measures which reveal the loss of purity of the vacuum due to restrictions to wedges and their horizons. Besides the well-known fact that localization-induced (generalized Hawking-) temperature is fixed by the geometric aspects, this area behavior (versus the standard volume dependence) constitutes the main difference between localization-caused and standard thermal behavior.Comment: 15 page Latex, dedicated to A. A. Belavin on the occasion of his 60th birthda

How far does the analogy between causal horizon-induced thermalization with the standard heat bath situation go?

After a short presentation of KMS states and modular theory as the unifying description of thermalizing systems we propose the absence of transverse vacuum fluctuations in the holographic projections as the mechanism for an area behavior (the transverse area) of localization entropy as opposed to the volume dependence of ordinary heat bath entropy. Thermalization through causal localization is not a property of QM, but results from the omnipresent vacuum polarization in QFT and does not require a Gibbs type ensemble avaraging (coupling to a heat bath).Comment: 10 pages, based on talk given at the 2002 Londrina Winter Schoo

The Effect of Gravitational Tidal Forces on Vacuum Polarization: How to Undress a Photon

The effect of gravitational tidal forces on photon propagation in curved spacetime is investigated. It is found that the imaginary part of the local refractive index Im n(u;w) may be negative as well as positive, corresponding to a local amplification as well as attenuation of the amplitude of the renormalized photon field. This is interpreted in terms of the effect of tidal forces on the virtual e^+e^- cloud surrounding the bare photon field---a positive/negative Im n(u;w) corresponds to an increased dressing/undressing of the bare photon. Below threshold decays of the photon to e^+e^- pairs can occur. Photon undressing in the vicinity of a black hole singularity is described as an example. These results are shown to be consistent with unitarity and the optical theorem in curved spacetime, which is derived here both in a local form and integrated over the photon trajectory.Comment: 13 pages, 1 figure, minor correction

Particle decays and stability on the de Sitter universe

We study particle decay in de Sitter space-time as given by first order perturbation theory in a Lagrangian interacting quantum field theory. We study in detail the adiabatic limit of the perturbative amplitude and compute the "phase space" coefficient exactly in the case of two equal particles produced in the disintegration. We show that for fields with masses above a critical mass $m_c$ there is no such thing as particle stability, so that decays forbidden in flat space-time do occur here. The lifetime of such a particle also turns out to be independent of its velocity when that lifetime is comparable with de Sitter radius. Particles with mass lower than critical have a completely different behavior: the masses of their decay products must obey quantification rules, and their lifetime is zero.Comment: Latex, 38 pages, 1 PostScript figure; added references, minor corrections and remark

The asymptotic symmetry of de Sitter spacetime

We show how to construct a set of Euclidean conformal correlation functions on the boundary of a de Sitter space from an interacting bulk quantum field theory with a certain asymptotic behaviour. We discuss the status of the boundary theory w.r.t. the reflection positivity and conclude that no obvious physical holographic interpretation is available.Comment: 12 pages, late

Microlocal analysis of quantum fields on curved spacetimes: Analytic wavefront sets and Reeh-Schlieder theorems

We show in this article that the Reeh-Schlieder property holds for states of quantum fields on real analytic spacetimes if they satisfy an analytic microlocal spectrum condition. This result holds in the setting of general quantum field theory, i.e. without assuming the quantum field to obey a specific equation of motion. Moreover, quasifree states of the Klein-Gordon field are further investigated in this work and the (analytic) microlocal spectrum condition is shown to be equivalent to simpler conditions. We also prove that any quasifree ground- or KMS-state of the Klein-Gordon field on a stationary real analytic spacetime fulfills the analytic microlocal spectrum condition.Comment: 31 pages, latex2

El comerç als centres urbans de la Regió Metropolitana de Barcelona

Malgrat els actius que indubtablement posseeix -renda de situació, fidelitat de la clientela-, el comerç en els centres urbans de la Regió Metropolitana de Barcelona coneix, en l'actualitat, dificultats evidents. Aquestes es deriven, en bona part, d'elements com l'obsolescència d'establiments, l'escassa inversió, la manca de sinergia entre les diverses activitats, la discontinuïtat dels baixos comercials i les dificultats de trànsit i aparcament. En aquestes circumstancies, el comerç dels centres s'ha trobat en una posició d'inferioritat enfront noves formes comercials -com les grans superfícies suburbanes- que, a més d'oferir preus molt competitius, disposen de fàcil accessibilitat, aparcament, màrqueting unitari i s'ajusten als nous hàbits de consum. Per perviure, el comerç dels centres urbans s'ha, doncs, de renovar de forma radical, tant pel que fa a la promoció, la tecnologia i els horaris, com a la cura de l'entorn. En aquest sentit, un element encoratjador és que darrerament la implantació de nous grans equipaments comercials en trama urbana -com I'Eix Macià de Sabadell o l'llla Diagonal de Barcelona- ha estat un element dinamitzador i no destructor del comerç en les Àrees que els envolten.A pesar de los activos que indudablemente posee -renta de situación, fidelidad de la clientela-, el comercio en los centros urbanos de la Región Metropolitana de Barcelona conoce en la actualidad dificultades evidentes. Estas se derivan, en buena parte, de elementos como la obsolescencia de los establecimientos, la escasa inversión, la falta de sinergía entre las distintas actividades, la discontinuidad de los bajos comerciales, así como de las dificultades de transito y aparcamiento. En estas circunstancias, el comercio de los centros urbanos se ha encontrado en una posición de inferioridad frente a nuevas formas comerciales -como las grandes superficies suburbanas- las cuales, además de ofrecer precios muy competitivos, disponen de fácil accesibilidad, aparcamiento, marketing unitario y se ajustan a los nuevos hábitos de consumo. Para pervivir, el comercio de los centros urbanos debe, pues, renovarse de manera radical, tanto por lo que se refiere a la promoción, la tecnología y los horarios, como al cuidado del entorno. En este sentido, un elemento alentador es que la implantación, en los últimos años, de nuevos grandes equipamientos comerciales en trama urbana -como el Eix Macià de Sabadell o la Illa Diagonal de Barcelona- ha sido un elemento dinamizador y no destructor del comercio en las áreas circunstantes

Efficient spin pumping into metallic SrVO3 epitaxial films

Spin pumping across interfaces between metallic SrVO3, where V is a 3d1 ion, epitaxial thin films and ferromagnetic Ni80Fe20 is reported. Data shows an efficient spin pumping with a spin mixing conductance value (g↑↓ = 11.8 × 1018 m− 2 ) similar to that reported in metallic Vanadium but significantly larger than that measured in isoelectronic (3d1 ) VO2, which displays a Mott transition. Data are rationalized in terms of the relevance of density of states at the Fermi level and the relative strength of electron-electron correlations and electron-lattice coupling as toggles to tune spin-mixing conductance across interfaces

De Sitter Waves and the Zero Curvature Limit

We show that a particular set of global modes for the massive de Sitter scalar field (the de Sitter waves) allows to manage the group representations and the Fourier transform in the flat (Minkowskian) limit. This is in opposition to the usual acceptance based on a previous result, suggesting the appearance of negative energy in the limit process. This method also confirms that the Euclidean vacuum, in de Sitter spacetime, has to be preferred as far as one wishes to recover ordinary QFT in the flat limit.Comment: 9 pages, latex no figure, to appear in Phys. Rev.