Quantum unitary dynamics in cosmological spacetimes

We address the question of unitary implementation of the dynamics for scalar fields in cosmological scenarios. Together with invariance under spatial isometries, the requirement of a unitary evolution singles out a rescaling of the scalar field and a unitary equivalence class of Fock representations for the associated canonical commutation relations. Moreover, this criterion provides as well a privileged quantization for the unscaled field, even though the associated dynamics is not unitarily implementable in that case. We discuss the relation between the initial data that determine the Fock representations in the rescaled and unscaled descriptions, and clarify that the S-matrix is well defined in both cases. In our discussion, we also comment on a recently proposed generalized notion of unitary implementation of the dynamics, making clear the difference with the standard unitarity criterion and showing that the two approaches are not equivalent.Comment: 18 page

Uniqueness of the Fock quantization of the Gowdy T3T^3 model

After its reduction by a gauge-fixing procedure, the family of linearly polarized Gowdy $T^3$ cosmologies admit a scalar field description whose evolution is governed by a Klein-Gordon type equation in a flat background in 1+1 dimensions with the spatial topology of $S^1$, though in the presence of a time-dependent potential. The model is still subject to a homogeneous constraint, which generates $S^1$-translations. Recently, a Fock quantization of this scalar field was introduced and shown to be unique under the requirements of unitarity of the dynamics and invariance under the gauge group of $S^1$-translations. In this work, we extend and complete this uniqueness result by considering other possible scalar field descriptions, resulting from reasonable field reparameterizations of the induced metric of the reduced model. In the reduced phase space, these alternate descriptions can be obtained by means of a time-dependent scaling of the field, the inverse scaling of its canonical momentum, and the possible addition of a time-dependent, linear contribution of the field to this momentum. Demanding again unitarity of the field dynamics and invariance under the gauge group, we prove that the alternate canonical pairs of fieldlike variables admit a Fock representation if and only if the scaling of the field is constant in time. In this case, there exists essentially a unique Fock representation, provided by the quantization constructed by Corichi, Cortez, and Mena Marugan. In particular, our analysis shows that the scalar field description proposed by Pierri does not admit a Fock quantization with the above unitarity and invariance properties.Comment: 14 page

Quantum Gowdy T3T^3 model: A uniqueness result

Modulo a homogeneous degree of freedom and a global constraint, the linearly polarised Gowdy $T^3$ cosmologies are equivalent to a free scalar field propagating in a fixed nonstationary background. Recently, a new field parameterisation was proposed for the metric of the Gowdy spacetimes such that the associated scalar field evolves in a flat background in 1+1 dimensions with the spatial topology of $S^1$, although subject to a time dependent potential. Introducing a suitable Fock quantisation for this scalar field, a quantum theory was constructed for the Gowdy model in which the dynamics is implemented as a unitary transformation. A question that was left open is whether one might adopt a different, nonequivalent Fock representation by selecting a distinct complex structure. The present work proves that the chosen Fock quantisation is in fact unique (up to unitary equivalence) if one demands unitary implementation of the dynamics and invariance under the group of constant $S^1$ translations. These translations are precisely those generated by the global constraint that remains on the Gowdy model. It is also shown that the proof of uniqueness in the choice of complex structure can be applied to more general field dynamics than that corresponding to the Gowdy cosmologies.Comment: 28 pages, minor changes, version accepted for publication in Classical and Quantum Gravit

Massless scalar field in de Sitter spacetime: unitary quantum time evolution

We prove that, under the standard conformal scaling, a massless field in de Sitter spacetime admits an O(4)-invariant Fock quantization such that time evolution is unitarily implemented. This result disproves previous claims in the literature. We discuss the relationship between this quantization with unitary dynamics and the family of O(4)-invariant Hadamard states given by Allen and Folacci, as well as with the Bunch-Davies vacuum.Comment: 23 pages. Typos corrected, matches published versio

Privatization and European Economic and Monetary Union

To qualify for full membership in the Economic and Monetary Union, member states had to meet strict budget deficit and government debt convergence criteria. This study analyzes whether deficits and indebtedness in the 1990s in Spain, Italy, Portugal and Greece were associated with a shift from privatization as a tool of economic restructuring, to privatization as a tool of European monetary convergence. The empirical results suggests that privatization funds accruing from the sale of state-owned enterprises in the Southern European countries might have been used to tackle budget deficits and meet the stringent criteria for monetary integration.Monetary Union; Privatization

Análisis de biomarcadores en la almeja Polymesoda caroliniana para la generación de un índice de salud y vulnerabilidad

El estudio de la vulnerabilidad depende del análisis de los elementos que la componen: exposición, sensibilidad y capacidad de recuperación. En este trabajo, se propone el uso de respuestas tisulares que se han recomendado como biomarcadores para medir los elementos de la vulnerabilidad en la almeja Polymesoda caroliniana, además de obtener un índice histopatológico para evaluar su estado de salud. El análisis histopatológico revela alteraciones que pueden ser producto del estrés ambiental, reflejando así, el nivel de sensibilidad. Mientras que el análisis inmunohistoquímico utiliza marcadores para determinar la presencia de compuestos tóxicos, lo que refleja el nivel de exposición de un organismo. En este trabajo se realizó un análisis de prevalencia de alteraciones tisulares en la glándula digestiva y el cálculo de un índice histopatológico para estimar el estado de salud. Se analizaron, además respuestas inmunohistoquímicas de tres marcadores de estrés ambiental (HSP70, MTs y CYP). Por otro lado, para la evaluación de la vulnerabilidad, se diseñó una estrategia semicuantitativa para determinar el nivel de exposición mediante el promedio de marcadores inmunohistoquímicos positivos en diferentes órganos. El nivel de sensibilidad fue determinado mediante la relación entre la prevalencia de alteraciones histopatológicas y el nivel de exposición. Finalmente, para estimar la capacidad de recuperación, se colocó al grupo control en un ambiente limpio durante 40 días. El promedio de marcadores inmunohistoquímicos positivos observados en la almeja la coloca en una categoría de exposición moderada. La relación entre la baja prevalencia de alteraciones y el nivel moderado de exposición de la almeja la coloca en una categoría de sensibilidad baja. Las almejas del grupo control permitieron observar la capacidad de revertir los efectos del estrés ambiental. Con las respuestas obtenidas mediante la evaluación de los elementos de la vulnerabilidad, la almeja P. caroliniana se ubica en una categoría de vulnerabilidad baja. La propuesta de evaluación presentada en esta tesis es una alternativa para la evaluación integral de los recursos acuáticos, busca además que en los estudios de vulnerabilidad se consideren las respuestas fisiológicas de los organismos. El análisis de respuestas fisiológicas de organismos se puede integrar en la evaluación de la vulnerabilidad de los sistemas acuáticos.The vulnerability depends on the analysis of the elements that compose it: exposure, sensitivity, and recovery capacity. In this work, the use of tissue responses that have been recommended as biomarkers to measure the elements of vulnerability in the Polymesoda caroliniana clam is proposed, in addition to obtaining a histopathological index to assess its health status. Histopathological analysis reveals alterations that may be the product of environmental stress, thus reflecting the level of sensitivity. While immunohistochemical analysis uses markers to determine the presence of toxic compounds, which reflects the level of exposure of an organism. In this work, an analysis of the prevalence of tissue alterations in the digestive gland and the calculation of a histopathological index to estimate health status was performed. Immunohistochemical responses of three environmental stress markers (HSP70, MTs and CYP) were also analyzed. On the other hand, for the vulnerability assessment, a semi-quantitative strategy was designed to determine the level of exposure through the average of positive immunohistochemical markers in different organs. The level of sensitivity was determined by the relationship between the prevalence of histopathological alterations and the level of exposure. Finally, to estimate the recovery capacity, the control group was placed in a clean environment for 40 days. The average number of positive immunohistochemical markers observed in the clam places it in a moderate exposure category. The relationship between the low prevalence of disorders and the moderate level of exposure of the clam places it in a category of low sensitivity. The clams of the control group allowed to observe the ability to reverse the effects of environmental stress. With the responses obtained by evaluating the elements of vulnerability, the P. caroliniana clam is located in a low vulnerability category. The evaluation proposal presented in this thesis is an alternative for the comprehensive evaluation of aquatic resources, it also seeks that in vulnerability studies the physiological responses of organisms are considered. Analysis of physiological responses of organisms can be integrated into the vulnerability assessment of aquatic systems

Engineering the reciprocal space for ultrathin GaAs solar cells

III-V solar cells dominate the high efficiency charts, but with significantly higher cost than other solar cells. Ultrathin III-V solar cells can exhibit lower production costs and immunity to short carrier diffusion lengths caused by radiation damage, dislocations, or native defects. Nevertheless, solving the incomplete optical absorption of sub-micron layers presents a challenge for light-trapping structures. Simple photonic crystals have high diffractive efficiencies, which are excellent for narrow-band applications. Random structures a broadband response instead but suffer from low diffraction efficiencies. Quasirandom (hyperuniform) structures lie in between providing high diffractive efficiency over a target wavelength range, broader than simple photonic crystals, but narrower than a random structure. In this work, we present a design method to evolve a simple photonic crystal into a quasirandom structure by modifying the spatial-Fourier space in a controlled manner. We apply these structures to an ultrathin GaAs solar cell of only 100 nm. We predict a photocurrent for the tested quasirandom structure of 25.3 mA/cm$^2$, while a planar structure would be limited to 16.1 mA/cm$^2$. The modified spatial-Fourier space in the quasirandom structure increases the amount of resonances, with a progression from discrete number of peaks to a continuum in the absorption. The enhancement in photocurrent is stable under angle variations because of this continuum. We also explore the robustness against changes in the real-space distribution of the quasirandom structures using different numerical seeds, simulating variations in a self-assembly method