Spherical collapse in chameleon models

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Angular-planar CMB power spectrum

Gaussianity and statistical isotropy of the Universe are modern cosmology's minimal set of hypotheses. In this work we introduce a new statistical test to detect observational deviations from this minimal set. By defining the temperature correlation function over the whole celestial sphere, we are able to independently quantify both angular and planar dependence (modulations) of the CMB temperature power spectrum over different slices of this sphere. Given that planar dependence leads to further modulations of the usual angular power spectrum C(l), this test can potentially reveal richer structures in the morphology of the primordial temperature field. We have also constructed an unbiased estimator for this angular-planar power spectrum which naturally generalizes the estimator for the usual C(l)'s. With the help of a chi-square analysis, we have used this estimator to search for observational deviations of statistical isotropy in WMAP's 5 year release data set (ILC5), where we found only slight anomalies on the angular scales l = 7 and l = 8. Since this angular-planar statistic is model-independent, it is ideal to employ in searches of statistical anisotropy (e.g., contaminations from the galactic plane) and to characterize non-Gaussianities.

Signatures of primordial non-Gaussianities in the matter power-spectrum and bispectrum: the time-RG approach

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Habermas lendo Peirce

Entre as várias referências feitas ao pensamento de Peirce, ao longo de sua carreira filosófica, dois textos foram tomados como exemplares da leitura que Jürgen Habermas faz do pensamento de Peirce e, ao lado das diferenças encontradas entre os dois textos, dois itens muito importantes se conservam: a verdadeira admiração pela virada pragmática promovida por aquele filósofo e cientista, que será seguida por seu leitor, e a séria restrição feita à progressiva tendência do pensamento de abandonar a intersubjetividade como garantia da objetividade da semiose, dando preferência a uma fundamentação cosmológica para todo conhecimento. Embora esta última restrição pudesse ser criticada em sua pertinência, tanto a admiração manifesta à contribuição feita por Peirce ao pensamento filosófico com sua proposta pragmática, quanto a restrição a um suposto abandono das relações pessoais na base da semiose, sem dúvida, manifestam o viés filosófico de Habermas lendo um autor que ele admira, mas que não pretende seguir como um exegeta.

Dark energy parametrizations and their effect on dark halos

There are a plethora of dark energy parametrizations that can fit current supernovae Ia data. However, these data are only sensitive to redshifts up to order one. In fact, many of these parametrizations break down at higher redshifts. In this paper we study the effect of dark energy models on the formation of dark halos. We select a couple of dark energy parametrizations which are sensible at high redshifts and compute their effect on the evolution of density perturbations in the linear and non-linear regimes. Using the Press-Schechter formalism we show that they produce distinguishable signatures in the number counts of dark halos. Therefore, future observations of galaxy clusters can provide complementary constraints on the behaviour of dark energy.

A simple model for quintessential inflation

We propose a simple toy model for quintessential inflation where a complex scalar field described by a Lagrangian with a U(1)(PQ) symmetry spontaneously broken at a high energy scale and explicitly broken by instanton effects at a much lower energy can account for both the early inflationary phase and the recent accelerated expansion of the Universe. The real part of the complex field plays the role of the in flaton whereas the imaginary part, the 'axion', is the quintessence field.

Fitting hyperbolic universes to Cayon-Smoot spots in COBE maps

On the possibility that the universe's matter density is low (Ohm(0) < 1), cosmologies can be considered with the metric of Friedmann's open universe but with closed hyperbolic manifolds as the physical three-space. These models have nontrivial spatial topology, with the property of producing multiple images of cosmic sources. Here a fit is attempted of 10 of these models to the physical cold and hot spots found by Cayon & Smoot in the COBE/DMR maps. These spots are interpreted as early, distant images of much nearer sources of inhomogeneity. The source for one of the cold spots is seen as the seed of a known supercluster.

NUMERICAL STUDY OF A PERTURBED EINSTEIN-DESITTER COSMOLOGICAL MODEL

Given the ever-increasing scale of structures discovered in the universe, we solve Einstein's equations numerically, under simplifying assumptions, to examine how this lack of uniformity affects the metric of Einstein-de Sitter cosmology. The results confirm the qualitative conclusion of Barrow, that a large density contrast is compatible with much smaller metric perturbations. The contribution of this peculiar gravity to the redshift might complicate studies of peculiar motions of galaxies, although it appears that the distortion is small for nearby clusters.

Analytic solutions for the Lambda-FRW model

The high precision attained by cosmological data in the last few years has increased the interest in exact solutions. Analytic expressions for solutions in the Standard Model are presented here for all combinations of Lambda = 0, Lambda not equal 0, kappa = 0, and kappa = 0, in the presence and absence of radiation and nonrelativistic matter. The most complete case (here called the Lambda gamma CDM Model) has Lambda not equal 0, kappa not equal 0, and supposes the presence of radiation and dust. It exhibits clearly the recent onset of acceleration. The treatment includes particular models of interest such as the Lambda CDM Model (which includes the cosmological constant plus cold dark matter as source constituents).

Thermal effects on the catalysis by a magnetic field

We show that the formation of condensates in the presence of a constant magnetic field in 2+1 dimensions is extremely unstable. It disappears as soon as a heat bath is introduced with or without a chemical potential. The value of the condensate as well as other observables are shown to become nonanalytic at finite temperature.

Initial-condition problem for a chiral Gross-Neveu system

A time-dependent projection technique is used to treat the initial-value problem for self-interacting fermionic fields. On the basis of the general dynamics of the fields, we derive formal equations of kinetic-type for the set of one-body dynamical variables. A nonperturbative mean-field expansion can be written for these equations. We treat this expansion in lowest order, which corresponds to the Gaussian mean-field approximation, for a uniform system described by the chiral Gross-Neveu Hamiltonian. Standard stationary features of the model, such as dynamical mass generation due to chiral symmetry breaking and a phenomenon analogous to dimensional transmutation, are reobtained in this context. The mean-field time evolution of nonequilibrium initial states is discussed.

Collective scattering of massive stars in higher order gravity

In the weak field approximation of higher order gravity theory a gravitational potential is described by a Newtonian plus a Yukawa-like term. This new term is used to explain some aspects of galactic dynamics, without considering dark matter. Its presence modifies the scattering probability of a massive intruder star and relaxation time of the stellar system.

Quartic fermion self-interactions in two-dimensional gauge theories

In this work we discuss the effect of quartic fermion self-interacting terms on the dynamically generated photon masses in 1+1 dimensions, for vector, chiral, and non-Abelian couplings. In the vector and chiral cases we find exactly the dynamically generated mass modified by the quartic term while in the non-Abelian case we find the dynamically generated mass associated with its Abelian part. We show that in the three cases there is a kind of duality between the gauge and quartic couplings. We perform functional as well as operator treatments allowing for the obtention of both fermion and vector field solutions. The structures of the Abelian models in terms of θ vacua are also addressed.

Discriminating new physics scenarios at the Next Linear Collider: The role of polarization

We explore the potential of the Next Linear Collider, operating in the e γ mode, to disentangle new physics scenarios in single W production. We study the effects related to the exchange of composite fermions in the reaction e γ→Wνe, and compare them with those arising from trilinear gauge boson anomalous couplings. We stress the role played by the initial state polarization to increase the reach of this machine and to discriminate the possible origin of the new phenomena.

Gravitational Lorentz force and the description of the gravitational interaction

In the context of a gauge theory for the translation group, we have obtained, for a spinless particle, a gravitational analogue of the Lorentz force. Then, we have shown that this force equation can be rewritten in terms of magnitudes related to either the teleparallel or the Riemannian structures induced in spacetime by the presence of the gravitational field. In the first case, it gives a force equation, with torsion playing the role of force. In the second, it gives the usual geodesic equation of general relativity. The main conclusion is that scalar matter is able to feel any one of the above spacetime geometries, the teleparallel and the metric ones. Furthermore, both descriptions are found to be completely equivalent in the sense that they give the same physical trajectory for a spinless particle in a gravitational field.