A uniqueness criterion for the Fock quantization of scalar fields with time dependent mass

A major problem in the quantization of fields in curved spacetimes is the ambiguity in the choice of a Fock representation for the canonical commutation relations. There exists an infinite number of choices leading to different physical predictions. In stationary scenarios, a common strategy is to select a vacuum (or a family of unitarily equivalent vacua) by requiring invariance under the spacetime symmetries. When stationarity is lost, a natural generalization consists in replacing time invariance by unitarity in the evolution. We prove that, when the spatial sections are compact, the criterion of a unitary dynamics, together with the invariance under the spatial isometries, suffices to select a unique family of Fock quantizations for a scalar field with time dependent mass.Comment: 11 pages, version accepted for publication in Classical and Quantum Gravit

Criteria for the determination of time dependent scalings in the Fock quantization of scalar fields with a time dependent mass in ultrastatic spacetimes

For Klein-Gordon fields, it is well known that there exist an infinite number of nonequivalent Fock representations of the canonical commutation relations and, therefore, of inequivalent quantum theories. A context in which this kind of ambiguities arises and prevents the derivation of robust results is, e.g., in the quantum analysis of cosmological perturbations. In these situations, typically, a suitable scaling of the field by a time dependent function leads to a description in an auxiliary static background, though the nonstationarity still shows up in a time dependent mass. For such a field description, and assuming the compactness of the spatial sections, we recently proved in three or less spatial dimensions that the criteria of a natural implementation of the spatial symmetries and of a unitary time evolution are able to select a unique class of unitarily equivalent vacua, and hence of Fock representations. In this work, we succeed to extend our uniqueness result to the consideration of all possible field descriptions that can be reached by a time dependent canonical transformation which, in particular, involves a scaling of the field by a function of time. This kind of canonical transformations modify the dynamics of the system and introduce a further ambiguity in its quantum description, exceeding the choice of a Fock representation. Remarkably, for any compact spatial manifold in less than four dimensions, we show that our criteria eliminate any possible nontrivial scaling of the field other than that leading to the description in an auxiliary static background. Besides, we show that either no time dependent redefinition of the field momentum is allowed or, if this may happen, the redefinition does not introduce any Fock representation that cannot be obtained by a unitary transformation.Comment: 37 pages. Modified title. Improved discussion concerning the spatial symmetry group. New section (section VI

Chemoinformatic Approach: The Case of Natural Products of Panama

Chemoinformatic analysis was used to characterize a compound database of natural products from Panama and other reference collections. Data mining allowed to compare drug-likeness properties with public and commercial software and to achieve a statistical analysis of the physicochemical properties. Visualization of the chemical space in 3D indicates a high structural similarity. Molecular flexibility and complexity were evaluated using 2D descriptors, whereas the molecular scaffold was obtained using the Murcko method, and these showed few differences between the explored data set. In this chapter, we also present and discuss an example of the application of the chemoinformatic approach using the concept of modeling the activity landscape to study the structure-activity relationships (SARs) of compounds with activity against Plasmodium falciparum

La incorporación de las mujeres a las Fuerzas Armadas: el caso español y su percepción pública en perspectiva comparada

Este trabajo examina la incorporación de las mujeres en las Fuerzas Armadas (FFAA) españolas. Desde un punto de vista teórico, el estudio se enmarca dentro de las discusiones acerca de la participación de las mujeres en las instituciones militares y de las diversas teorías sobre los factores que influyen y explican este proceso. Además, el examen empírico del caso español se contextualiza en términos comparados con información general relativa a la feminización de las fuerzas militares de los países de la OTAN y más particularmente del caso de EEUU. A la luz de la política de incorporación femenina a las FFAA españolas se concluye que desde un punto de vista institucional el proceso se encuentra básicamente completado y además con un porcentaje de feminización de los más altos entre los países miembros de la OTAN. En cuanto a la dimensión social del cambio y de su percepción pública, sin embargo, existen importantes contradicciones y los estereotipos culturalmente arraigados continúan aislando a las mujeres de tareas tradicionalmente percibidas como masculinas

Uniqueness of the Fock quantization of scalar fields in a Bianchi I cosmology with unitary dynamics

The Fock quantization of free scalar fields is subject to an infinite ambiguity when it comes to choosing a set of annihilation and creation operators, choice that is equivalent to the determination of a vacuum state. In highly symmetric situations, this ambiguity can be removed by asking vacuum invariance under the symmetries of the system. Similarly, in stationary backgrounds, one can demand time-translation invariance plus positivity of the energy. However, in more general situations, additional criteria are needed. For the case of free (test) fields minimally coupled to a homogeneous and isotropic cosmology, it has been proven that the ambiguity is resolved by introducing the criterion of unitary implementability of the quantum dynamics, as an endomorphism in Fock space. This condition determines a specific separation of the time dependence of the field, so that this splits into a very precise background dependence and a genuine quantum evolution. Furthermore, together with the condition of vacuum invariance under the spatial Killing symmetries, unitarity of the dynamics selects a unique Fock representation for the canonical commutation relations, up to unitary equivalence. In this work, we generalize these results to anisotropic spacetimes with shear, which are therefore not conformally symmetric, by considering the case of a free scalar field in a Bianchi I cosmology.Comment: 23 pages. Updated to match published versio

A unique Fock quantization for fields in non-stationary spacetimes

In curved spacetimes, the lack of criteria for the construction of a unique quantization is a fundamental problem undermining the significance of the predictions of quantum field theory. Inequivalent quantizations lead to different physics. Recently, however, some uniqueness results have been obtained for fields in non-stationary settings. In particular, for vacua that are invariant under the background symmetries, a unitary implementation of the classical evolution suffices to pick up a unique Fock quantization in the case of Klein-Gordon fields with time-dependent mass, propagating in a static spacetime whose spatial sections are three-spheres. In fact, the field equation can be reinterpreted as describing the propagation in a Friedmann-Robertson-Walker spacetime after a suitable scaling of the field by a function of time. For this class of fields, we prove here an even stronger result about the Fock quantization: the uniqueness persists when one allows for linear time-dependent transformations of the field in order to account for a scaling by background functions. In total, paying attention to the dynamics, there exists a preferred choice of quantum field, and only one $SO(4)$-invariant Fock representation for it that respects the standard probabilistic interpretation along the evolution. The result has relevant implications e.g. in cosmology.Comment: Typos correcte

Uniqueness of the Fock quantization of fields with unitary dynamics in nonstationary spacetimes

The Fock quantization of fields propagating in cosmological spacetimes is not uniquely determined because of several reasons. Apart from the ambiguity in the choice of the quantum representation of the canonical commutation relations, there also exists certain freedom in the choice of field: one can scale it arbitrarily absorbing background functions, which are spatially homogeneous but depend on time. Each nontrivial scaling turns out into a different dynamics and, in general, into an inequivalent quantum field theory. In this work we analyze this freedom at the quantum level for a scalar field in a nonstationary, homogeneous spacetime whose spatial sections have $S^3$ topology. A scaling of the configuration variable is introduced as part of a linear, time dependent canonical transformation in phase space. In this context, we prove in full detail a uniqueness result about the Fock quantization requiring that the dynamics be unitary and the spatial symmetries of the field equations have a natural unitary implementation. The main conclusion is that, with those requirements, only one particular canonical transformation is allowed, and thus only one choice of field-momentum pair (up to irrelevant constant scalings). This complements another previous uniqueness result for scalar fields with a time varying mass on $S^3$, which selects a specific equivalence class of Fock representations of the canonical commutation relations under the conditions of a unitary evolution and the invariance of the vacuum under the background symmetries. In total, the combination of these two different statements of uniqueness picks up a unique Fock quantization for the system. We also extend our proof of uniqueness to other compact topologies and spacetime dimensions.Comment: 12 page

Validation of SMOS L2 and L3 soil moisture products over the Duero Basin at different spatial scales

36th International Symposium on Remote Sensing of Environment, 11-15 May 2015, Berlin, Germany.-- 6 pages, 3 figures, 3 tablesAn increasing number of permanent soil moisture measurement networks are nowadays providing the means for validating new remotely sensed soil moisture estimates such as those provided by the ESA’s Soil Moisture and Ocean Salinity (SMOS) mission. Two types of in situ measurement networks can be found: small-scale (100–10000 km2), which provide multiple ground measurements within a single satellite footprint, and large-scale (>10000 km2), which contain a single point observation per satellite footprint. This work presents the results of a comprehensive spatial and temporal validation of a long-term (January, 2010 to June, 2014) dataset of SMOS-derived soil moisture estimates using two in situ networks within the Duero basin (Spain). The first one is the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS), which has been extensively applied for validation of soil moisture remote sensing observations, including SMOS. REMEDHUS can be considered within the small-scale network group (1300 km2). The other network started from an existing meteorological network from the Castilla y León region, where soil moisture probes were incorporated in 2012. This network can be considered within the large-scale group (65000 km2). Results from comparison to in situ show that the new reprocessed L2 product (v5.51) improves the accuracy of former soil moisture retrievals, making them suitable for developing new L3 products. Validation based on comparisons between dense/sparse networks showed that temporal patterns on soil moisture are well reproduced, whereas spatial patterns are difficult to depict given the different spatial representativeness of ground and satellite observationsThis work was supported by the Spanish Ministry of Economy and Competitiveness (Project AYA2012-39356-C05). Ángela Gumuzzio acknowledges support from the FPI grant BES-2011-050439Peer Reviewe

Kitchen Company : e-commerce

Fil: Galache de Toro, Agustín. Universidad de San Andrés. Escuela de Negocios; Argentina.Fil: Olmedo, José A. Universidad de San Andrés. Escuela de Negocios; Argentina.Postigo, Sergi

Evaluacion economica del paso Internacional Pehuenche

141 p.La presente memoria ha considerado relevante calcular los costos de transporte caminero para las dos variantes que actualmente posee el Paso Pehuenche ( Los Cóndores y El Campanario ), esta importante información ayudara a decidir acerca de la conveniencia de optar por una u otra alternativa. Dentro de los principales costos a determinar están los costos de transporte y costos de tiempo para las personas, estos costos se determinaran para las dos variantes: Los Cóndores y El Campanario. En el calculo se asume que la calidad de las variantes no influirá en la decisión de utilizar el Paso Pehuenche, además el transito actual y proyectado será el mismo para ambas alternativas; es decir, supondremos que cualquier vehículo que llegue al Paso Pehuenche cruzara la cordillera utilizando la ruta de la Cuesta Los Cóndores o de la Variante Campanario ( se ha considerado este supuesto incluso aunque existan casi 7 Km. de diferencia, ya que así se podrá realizar una comparación de los costos en que las diferencias se produzcan no solo por distancias, sino también por las características técnicas de los caminos). De esta manera se podrá determinar cual variante posee menores costos de transporte (costos de operación y tiempo de viaje) para una demanda de transito igual. Para determinar los costos de ambas vías se utilizara el modelo HDM3, que actualmente usa el Ministerio de Obras Publicas en la Evaluación Social de Proyectos Camineros. La presente memoria pretende contribuir en las decisiones económicas de este proyecto, decisiones que afectaran la competitividad de empresas Chilenas que exportan hacia países del conosur; también se debe mencionar que Chile generaría una Buena imagen como Pals al tener un paso internacional complementario al paso Los Libertadores Conclusiones y Recomendaciones: En base a los resultados que arrojo este estudio se pudo concluir que en el corto y el mediano plazo la construcción del paso El Pehuenche, se debería realizar por la Cuesta Los Cóndores la cual posee para 20 anos un VAN (12%) de $-18.654.473.447 , en cambio el VAN (12$ - 20.494.310.302. La mejor o la menos mala de las alternativas es la Cuesta Los Cóndores; en cambio si consideramos un horizonte de tiempo mas lejano esta decisión podría cambiar porque la alternativa Variante Campanario posee ahorros de costos crecientes, lo que podría cubrir la mayor inversión que implica la construcción de la alternativa Variante Campanario. Considerando el valor actual neto de ambas alternativas, se recomienda la creación de un peaje, el cual generaría ingresos y permitiría que el proyecto a un mediano y largo plazo sea rentable. Se determine un peaje de equilibrio, es decir un valor de peaje por tipo de automóvil que cubriera los montos de Inversión y los costos operacionales de cada alternativa. Se calculo que el peaje de equilibrio para 30 años, de la Cuesta Los Cóndores seria de $10.866 para automóviles y$21.733 para buses y camiones ( Considerando como ano 1 el ano 2003 ), en cambio para la Variante Campanario el valor de peaje seria de $11.677 y$23.353 respectivamente. El mayor valor de peaje para la Variante Campanario se explica principalmente por el mayor monto de inversión que posee esta alternativa en relación a la Cuesta Los Cóndores. De acuerdo a los resultados mencionados se concluyo que para el proyecto de 30 anos el peaje de la Variante Campanario es un 7,45% mayor que de la Cuesta Los Cóndores, sin embargo, si el proyecto tuviera una duración de 40 anos, la variación entre los valores de peaje de ambas alternativas seria de 6,3%, es decir, a medida que el proyecto aumenta su duración , la variación mencionada bajara aún mas; por lo tanto a un largo plazo la Variante Campanario disminuirá su desventaja en relación a la Cuesta Los Cóndores respecto del valor de peaje