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Search Results: 1 - 10 of 8966 matches for " Alejandro Gangui "
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The National Library of Argentina: exhibiting astronomy-related rare books
Alejandro Gangui
Physics , 2009,
Abstract: Astronomical and cosmological knowledge up to the dawn of modern science was profoundly embedded in myth, religion and superstition. Many of these inventions of the human mind remain today stored in different supports: medieval engravings, illuminated manuscripts, and of course also in old and rare books.
El universo de Einstein: 1905 - annus mirabilis - 2005
Alejandro Gangui
Physics , 2007,
Abstract: Year 2005 was the World Year of Physics, and it was commemorated worldwide as the 100th anniversary of Albert Einstein's legendary works in which the foundations of at least three areas of modern physics were laid: statistical mechanics, quantum mechanics and special relativity. These works turned year 1905 in what deservedly was called the "miraculous year" (annus mirabilis) of Einstein. However, the influence of this great mind was not limited to science. As it is well known, his fingerprint remains engraved in many aspects of our daily life. Because of that, in this work we have tried to cover almost all the subjects in which Einstein was involved during the last century and, of course, try and reveal the future projection his actions will have in this new century that has just begun. Among the subjects covered in the volume one can find the possible connection between Einstein and the artistic vanguard movement, his religiosity, his days in Argentina, the Nobel Prize, the Einstein-Freud correspondence, his pacifism and the nuclear energy, science and politics under the Second Empire and the Weimar Republic, and even a description of his patents and experiments, the studies performed to search for "built-in" features in his brain and the doubts many had regarding whether Einstein was a genius or a crank. Also included are essays on Einstein and Borges, philosophy and relativity, Mach's principle, the relation among science, arts and humanities, and, closer to Einstein's own theoretical research, the twin paradox, chance and quantum mechanics, the arrow of time, gravitational lenses, string theory, holography and black holes, gravitomagnetism, superconductivity, gravitational waves, the photoelectric effect and the alternative theories for gravitation.
CMB Anisotropies and Theories of the Early Universe
Alejandro Gangui
Physics , 1995,
Abstract: I present recent work aimed at showing how currently competing theories of the early universe leave their imprint on the temperature anisotropies of the CMB radiation. We consider the 3-point correlation function, as well as the inherent theoretical uncertainties associated with it, for which we derive explicit analytic formulae. We apply them in the study of non-Gaussian features that arise on large scales in the framework of both inflationary and topological defects models. For inflation, we develop a perturbative analysis for the study of spatial correlations in the inflaton in the context of the stochastic approach to inflation. We also include an analysis of a particular geometry, the so-called `collapsed' 3-point function, in the case of post recombination integrated effects, arising generically whenever the mildly non linear growth of perturbations is taken into account. We also devote a part of the thesis to the study of recently proposed analytic models of topological defects, and implement them in the analysis of both the CMB excess kurtosis (for cosmic strings) and the CMB collapsed 3-point function and skewness (for textures). Lastly, we present a study of the CMB anisotropies on the degree angular scale in the framework of the global texture scenario, and show the relevant features that arise; among these, the Doppler peaks.
Non--Gaussian Effects in the Cosmic Microwave Background from Inflation
Alejandro Gangui
Physics , 1994, DOI: 10.1103/PhysRevD.50.3684
Abstract: The presence of non--Gaussian features in the Cosmic Microwave Background (CMB) radiation maps represents one of the most long--awaited clues in the search for the actual structure of the primordial radiation, still needing confirmation. These features could shed some light on the non trivial task of distinguishing the real source of the primeval perturbations leading to large scale structure. One of the simplest non--Gaussian signals to search is the (dimensionless) skewness ${\cal S}$. Explicit computations for ${\cal S}$ are presented in the frame of physically motivated inflationary models (natural, intermediate and polynomial potential inflation) in the hope of finding values in agreement with estimated quantities from large angle scale (e.g., {\em COBE} DMR) maps. In all the cases considered the non--Gaussian effects turn out to lie below the level of theoretical uncertainty (cosmic variance). The possibility of unveiling the signal for ${\cal S}$ with multiple--field models is also discussed.
Primordial Non-Gaussian Signatures in the Sky
Alejandro Gangui
Physics , 1994, DOI: 10.1007/3-540-60024-8_85
Abstract: The presence of non-Gaussian features in the CMB radiation maps represents one of the most long-awaited clues in the search for the actual structure of the primordial radiation. These features could shed some light on the non trivial task of distinguishing the real source of the primeval perturbations leading to large scale structure. In the present paper we briefly review recent work towards finding analytical estimates of the three- and four-point correlation functions and of their zero-lag limits, namely, the skewness and kurtosis, respectively. - Contributed talk to appear in the proceedings of "Birth of the Universe & Fundamental Physics", May 18-21, 1994, Rome, Italy.
Non-Gaussian Fluctuations From Textures
Alejandro Gangui
Physics , 1996,
Abstract: One of the most powerful tools to probe the existence of cosmic defects in the early universe is through the Cosmic Microwave Background (CMB) radiation. It is well known that computations with causal sources are more involved than the adiabatic counterparts based on inflation, and this fact has in part hampered the development of fine detailed predictions. Analytical modeling, while necessarily limited in power, may tell us the overall characteristics of CMB from defects and hint at new features. We apply an analytical model for textures to the study of non-Gaussian features of the CMB sky and compare our predictions with the four-year COBE-DMR data.
Early Universe Sources for Cosmic Microwave Background Non-Gaussianity
Alejandro Gangui
Physics , 2003,
Abstract: In the framework of inflationary models with non-vacuum initial states for cosmological perturbations, we study non-Gaussian signatures on the cosmic microwave background radiation produced by a broken-scale-invariant model which incorporates a feature at a privileged scale in the primordial power spectrum.
The best unbiased estimator for the CMB angular bispectrum
Alejandro Gangui
Physics , 2000,
Abstract: For those angular multipoles where cosmic variance is an issue, non-Gaussianities in the Cosmic Microwave Background (CMB) anisotropies will be hard to detect. Here, we construct explicitly the best unbiased estimator for the CMB angular bispectrum.
The cosmology of the Divine Comedy
Alejandro Gangui
Physics , 2008,
Abstract: Since the time of ancient civilizations, cosmology had a privileged place within the various artistic and literary manifestations. The Divine Comedy by Dante Alighieri, one of the masterpieces in literature and thought of the Western World, is organized on the image of the cosmos of the XIII century, which is analyzed in this article.
Dante, astrology and astronomy
Alejandro Gangui
Physics , 2008,
Abstract: Some verses of Dante Alighieri suggest his astrological sign and his probable date of birth. This leads us to reflect on the different methods, increasingly divergent, with which sciences as opposed to beliefs approach reality.
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