Studies on Some Aspects of the Physics of the Early Universe Using Gravitationally Coupled Scalar Field –

This thesis deals with some aspects of the Physics of the early universe, like phase transitions, bubble nucleations and premodial density perturbations which lead to the formation structures in the universe. Quantum aspects of the gravitational interaction play an essential role in retical high-energy physics. The questions of the quantum gravity are naturally connected with early universe and Grand Unification Theories. In spite of numerous efforts, the various problems of quantum gravity remain still unsolved. In this condition, the consideration of different quantum gravity models is an inevitable stage to study the quantum aspects of gravitational interaction. The important role of gravitationally coupled scalar field in the physics of the early universe is discussed in this thesis. The study shows that the scalar-gravitational coupling and the scalar curvature did play a crucial role in determining the nature of phase transitions that took place in the early universe. The key idea in studying the formation structure in the universe is that of gravitational instability.

Analysis of Fluctuations in the Early Universe Using Fokker-Planck Formalism

The thesis begins with a review of basic elements of general theory of relativity (GTR) which forms the basis for the theoretical interpretation of the observations in cosmology. The first chapter also discusses the standard model in cosmology, namely the Friedmann model, its predictions and problems. We have also made a brief discussion on fractals and inflation of the early universe in the first chapter. In the second chapter we discuss the formulation of a new approach to cosmology namely a stochastic approach. In this model, the dynam ics of the early universe is described by a set of non-deterministic, Langevin type equations and we derive the solutions using the Fokker—Planck formalism. Here we demonstrate how the problems with the standard model, can be eliminated by introducing the idea of stochastic fluctuations in the early universe. Many recent observations indicate that the present universe may be approximated by a many component fluid and we assume that only the total energy density is conserved. This, in turn, leads to energy transfer between different components of the cosmic fluid and fluctuations in such energy transfer can certainly induce fluctuations in the mean to factor in the equation of state p = wp, resulting in a fluctuating expansion rate for the universe. The third chapter discusses the stochastic evolution of the cosmological parameters in the early universe, using the new approach. The penultimate chapter is about the refinements to be made in the present model, by means of a new deterministic model The concluding chapter presents a discussion on other problems with the conventional cosmology, like fractal correlation of galactic distribution. The author attempts an explanation for this problem using the stochastic approach.

Cosmología en la obra de Dante Alighieri

Este ensayo busca mostrar la síntesis del pensamiento griego y cristiano en materia de cosmología, síntesis que operó a lo largo de la edad media y que encontró su mayor expresión literaria en Dante.

The Inner Meaning of Outer Space: Human Nature and the Celestial Realm

Kant argued that humans possess a priori knowledge of space; although his argument focused on a physics of bodies, it also has implications for a psychology of beings. Many human cultures organize stars in the night sky into constellations (i.e., impose structure); attribute properties, behaviors, and abilities to objects in the celestial realm (i.e., impose meaning); and use perceived regularity in the celestial realms in development of calendars, long-range navigation, agriculture, and astrology (i.e., seek predictability and control). The physical inaccessibility of the celestial realm allows a potent source of metaphor, and also allows projection of myths regarding origin and ascension, places of power, and dwelling places of gods, immortals, and other souls. Developments in astronomy and cosmology influenced views of human nature and the place of humanity in the universe, and these changes parallel declines in egocentrism with human development. Views regarding alleged beings (e.g., angels, extraterrestrials) from the celestial realm (and to how communicate with such beings) are anthropocentric and ignore evolutionary factors in physical and cognitive development. It is suggested that in considering views and uses of the celestial realm, we learn not just about the universe, but also about ourselves. 

Plotino y Grosseteste: El neoplatonismo en la cosmología medieval

En este trabajo se estudia el caso de la cosmología del filósofo y científico Robert Grosseteste como un ejemplo de la notable influencia del neoplatonismo en la ciencia medieval. Uno de los propósitos de la cosmología de Grosseteste consistió en explicar la secuencia efectiva de la creación del cosmos. Sostengo que la explicación que ofrece Grosseteste acerca de la creación es una expresión renovada de algunas ideas de Plotino a propósito de cómo el Uno engendra lo múltiple. Me interesa resaltar tres aspectos de la estrecha relación entre el sistema cosmológico de Grosseteste y el sistema metafísico de Plotino: (1) Unidad de principio, (2) Mecanismos de generación y (3) Unidad del sistema.

La Crisis ambiental como proceso. Un análisis reflexivo sobre su emergencia, desarrollo y profundización desde la perspectiva de la teoría crítica

La investigación se focaliza en el análisis de la crisis ambiental considerada como un fenómeno complejo de evolución incierta producto de un proceso socio histórico, cuyos orígenes se remontan a los albores del proyecto moderno y deben rastrearse en un cúmulo de circunstancias que expresan las contradicciones de un modelo socioeconómico identificado con el crecimiento sostenido de la producción y las magnitudes económicas. Partiendo de esta base, se propone abordar la relación entre saber sociológico y crisis ambiental, a partir de las contribuciones de la teoría crítica a la compresión de las causas profundas de la crisis ambiental y de sus elementos constitutivos. Para lo cual se propone profundizar en algunas categorías desarrolladas por la corriente social crítica, las cuales si bien no se refieren en forma directa a la problemática ambiental, se vislumbran como campos fértiles para comprender los procesos sociales generadores de la crisis ambiental así como las alternativas que han de adoptarse para su resolución, teniendo en cuenta los mecanismos que ejerce el sistema para neutralizar los cambios que implica la conformación de una racionalidad alternativa. Acorde con ello, la primera parte del trabajo se centra en el abordaje de la relación sociedad naturaleza en el marco de tres grandes procesos sociales identificados como cosmológico, teocéntrico y antropocéntrico, haciendo especial hincapié en la correlación que en cada una de las etapas consideradas se establece entre racionalidad dominante, producción de conocimiento y conceptualización de naturaleza. El segundo capítulo profundiza en los efectos de la racionalidad instrumental sobre la ruptura del proyecto moderno y su incidencia sobre la emergencia de la crisis ambiental, a partir de la posición adoptada por Heidegger y por los referentes de la Escuela de Frankfurt. Posteriormente el análisis se estructura en torno a las dimensiones críticas de la modernidad avanzada, considerada como contexto situacional de desarrollo y profundización de la crisis ambiental, teniendo en cuenta los aportes teóricos desarrollados por Zygmunt Bauman e Immanuel Wallerstein. Al finalizar se presentan las conclusiones generales de la tesis y las posibles líneas de investigación que se abren a partir del trabajo desarrollado.

Livestock vaccine adoption among poor farmers in Bolivia: Remembering innovation diffusion theory

The paper explores the low uptake of livestock vaccination among poor farming communities in Bolivia utilising core elements of the original innovation diffusion theory. Contrary to the recent literature, we found that vaccination behaviour was strongly Linked to social and cultural, rather than economic, drivers. While membership in a group increased uptake, the 'hot' and 'cold' distinctions which dictate health versus illness within Andean cosmology also played a role, with vaccination viewed as a means of addressing underlying imbalances. We concluded that uptake of livestock vaccination was unlikely to improve without knowledge transfer that acknowledges local. epistemologies for Livestock disease. (C) 2008 Elsevier Ltd. All rights reserved.

Nested parallelism for multi-core HPC systems using Java

Since its introduction in 1993, the Message Passing Interface (MPI) has become a de facto standard for writing High Performance Computing (HPC) applications on clusters and Massively Parallel Processors (MPPs). The recent emergence of multi-core processor systems presents a new challenge for established parallel programming paradigms, including those based on MPI. This paper presents a new Java messaging system called MPJ Express. Using this system, we exploit multiple levels of parallelism - messaging and threading - to improve application performance on multi-core processors. We refer to our approach as nested parallelism. This MPI-like Java library can support nested parallelism by using Java or Java OpenMP (JOMP) threads within an MPJ Express process. Practicality of this approach is assessed by porting to Java a massively parallel structure formation code from Cosmology called Gadget-2. We introduce nested parallelism in the Java version of the simulation code and report good speed-ups. To the best of our knowledge it is the first time this kind of hybrid parallelism is demonstrated in a high performance Java application. (C) 2009 Elsevier Inc. All rights reserved.

The earth, the sky and the water's edge: changing beliefs in the earlier prehistory of Northern Europe

There have been two kinds of study of ancient beliefs in the earlier prehistory of Scandinavia. One considers the impact of ideas which originated further to the south and east. It considers a cosmology based on the movements of the sun. A second tradition develops out of the ethnography of the circumpolar region and combines archaeological evidence with the beliefs of hunter-gatherers. It postulates the existence of a three-tier cosmology in which people could communicate between different worlds. This paper argues that certain elements that are thought to epitomize the ‘Southern’ system might have been suggested by existing ideas within Scandinavia itself. Both sets of beliefs came to influence one another, but they became increasingly distinct towards the end of the Bronze Age. This paper reconsiders the rock carvings, metalwork and mortuary cairns of that period and the Iron Age in relation to the process of religious change.

Transition redshift: new kinematic constraints from supernovae

The transition redshift (deceleration/acceleration) is discussed by expanding the deceleration parameter to first order around its present value. A detailed study is carried out by considering two different parametrizations, q = q(0) + q(1)z and q = q(0) + q(1)z(1 + z)(-1), and the associated free parameters (q(0), q(1)) are constrained by three different supernovae (SNe) samples. A previous analysis by Riess et al. using the first expansion is slightly improved and confirmed in light of their recent data (Gold07 sample). However, by fitting the model with the Supernova Legacy Survey (SNLS) type Ia sample, we find that the best fit to the redshift transition is z(t) = 0.61, instead of z(t) = 0.46 as derived by the High-z Supernovae Search (HZSNS) team. This result based in the SNLS sample is also in good agreement with the sample of Davis et al., z(t) = 0.60(-0.11)(+0.28) (1 sigma). Such results are in line with some independent analyses and accommodate more easily the concordance flat model (Lambda CDM). For both parametrizations, the three SNe Ia samples considered favour recent acceleration and past deceleration with a high degree of statistical confidence level. All the kinematic results presented here depend neither on the validity of general relativity nor on the matter-energy contents of the Universe.

Evolution of primordial black holes in a radiation and phantom energy environment

In this work we extend previous work on the evolution of a primordial black hole (PBH) to address the presence of a dark energy component with a super-negative equation of state as a background, investigating the competition between the radiation accretion, the Hawking evaporation and the phantom accretion, the latter two causing a decrease on black hole mass. It is found that there is an instant during the matter-dominated era after which the radiation accretion becomes negligible compared to the phantom accretion. The Hawking evaporation may become important again depending on a mass threshold. The evaporation of PBHs is quite modified at late times by these effects, but only if the generalized second law of thermodynamics is violated.

Photometric redshifts and k-corrections for the Sloan Digital Sky Survey Data Release 7

We present a catalogue of galaxy photometric redshifts and k-corrections for the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7), available on the World Wide Web. The photometric redshifts were estimated with an artificial neural network using five ugriz bands, concentration indices and Petrosian radii in the g and r bands. We have explored our redshift estimates with different training sets, thus concluding that the best choice for improving redshift accuracy comprises the main galaxy sample (MGS), the luminous red galaxies and the galaxies of active galactic nuclei covering the redshift range 0 < z < 0.3. For the MGS, the photometric redshift estimates agree with the spectroscopic values within rms = 0.0227. The distribution of photometric redshifts derived in the range 0 < z(phot) < 0.6 agrees well with the model predictions. k-corrections were derived by calibration of the k-correct_v4.2 code results for the MGS with the reference-frame (z = 0.1) (g - r) colours. We adopt a linear dependence of k-corrections on redshift and (g - r) colours that provide suitable distributions of luminosity and colours for galaxies up to redshift z(phot) = 0.6 comparable to the results in the literature. Thus, our k-correction estimate procedure is a powerful, low computational time algorithm capable of reproducing suitable results that can be used for testing galaxy properties at intermediate redshifts using the large SDSS data base.

Morphological properties of superclusters of galaxies

We studied superclusters of galaxies in a volume-limited sample extracted from the Sloan Digital Sky Survey Data Release 7 and from mock catalogues based on a semi-analytical model of galaxy evolution in the Millennium Simulation. A density field method was applied to a sample of galaxies brighter than M(r) = -21+5 log h(100) to identify superclusters, taking into account selection and boundary effects. In order to evaluate the influence of the threshold density, we have chosen two thresholds: the first maximizes the number of objects (D1) and the second constrains the maximum supercluster size to similar to 120 h(-1) Mpc (D2). We have performed a morphological analysis, using Minkowski Functionals, based on a parameter, which increases monotonically from filaments to pancakes. An anticorrelation was found between supercluster richness (and total luminosity or size) and the morphological parameter, indicating that filamentary structures tend to be richer, larger and more luminous than pancakes in both observed and mock catalogues. We have also used the mock samples to compare supercluster morphologies identified in position and velocity spaces, concluding that our morphological classification is not biased by the peculiar velocities. Monte Carlo simulations designed to investigate the reliability of our results with respect to random fluctuations show that these results are robust. Our analysis indicates that filaments and pancakes present different luminosity and size distributions.

DENSITY PROFILE, VELOCITY ANISOTROPY, AND LINE-OF-SIGHT EXTERNAL CONVERGENCE OF SLACS GRAVITATIONAL LENSES

Data from 58 strong-lensing events surveyed by the Sloan Lens ACS Survey are used to estimate the projected galaxy mass inside their Einstein radii by two independent methods: stellar dynamics and strong gravitational lensing. We perform a joint analysis of these two estimates inside models with up to three degrees of freedom with respect to the lens density profile, stellar velocity anisotropy, and line-of-sight (LOS) external convergence, which incorporates the effect of the large-scale structure on strong lensing. A Bayesian analysis is employed to estimate the model parameters, evaluate their significance, and compare models. We find that the data favor Jaffe`s light profile over Hernquist`s, but that any particular choice between these two does not change the qualitative conclusions with respect to the features of the system that we investigate. The density profile is compatible with an isothermal, being sightly steeper and having an uncertainty in the logarithmic slope of the order of 5% in models that take into account a prior ignorance on anisotropy and external convergence. We identify a considerable degeneracy between the density profile slope and the anisotropy parameter, which largely increases the uncertainties in the estimates of these parameters, but we encounter no evidence in favor of an anisotropic velocity distribution on average for the whole sample. An LOS external convergence following a prior probability distribution given by cosmology has a small effect on the estimation of the lens density profile, but can increase the dispersion of its value by nearly 40%.