Repositório RCAAP

Methods of K-theory and spectral theory of Dirac operators are applied to describe the Chern isomorphisms and quantum fields on branes on hyperbolic manifolds.

In this work, I intend to show a possible candidate of inflaton potential V(phi) in a scenario of a brane world defined by a pair of branes (RS-I).

We study the scalar perturbations of rotating black holes in framework of extra dimensions type Randall-Sundrum(RS).

The aim of this work is to present a possible way to estimate observational electromagnetical clues in the spectrum of quasars and microquasars due to the presence of extra dimensions. Here we analyze two possible ways to detect these electromagnetic signals: by the brane corrected accretion mechanism and by production of electromagnetic KK modes. We show that for the static black hole accretion case, the brane corrections cause a extremelly small variation in the luminosity of the quasar. For the electromagnetic KK modes case, apparently the answer for the biggest quasars is positive and on the other hand, the possibility that microquasars can present constraints on extra-dimensional gravity in their spectra is less probable.

We take arbitrary gravitational perturbations of a 5d spacetime and reduce it to the form an axially symmetric warped braneworld. Then, we write the filed equations for the linearized gravity perturbations. We obtain the equations that describes the graviton, gravivector and the graviscalar fluctuations and analyse the effects of the Schrödinger potentials that appear in these equations.

Since the proposal of the AdS/CFT correspondence, made by Maldacena and Witten, there has been some controversy about the definition of conserved Noether charges associated with asymptotic isometries in asymptotically AdS spacetimes, namely, whether they form an anomalous (i.e., a nontrivial central extension) representation of the Lie algebra of the conformal group in odd bulk dimensions or not. In the present work, we shall review the derivation of these charges by using covariant phase space techniques, emphasizing the principle of locality underlying it. We shall also comment on how these issues manifest themselves in the quantum setting.

In this work we study a scalar perturbation in a brane black hole with Schwarzschild behavior, localized on the brane. This black hole solution was derived by Casadio, Fabbri and Mazzacurati with the metric satisfying the condition R = 0, where R is the four-dimensional scalar curvature.

The Poincaré superalgebra is introduced from a generalization of the Cartan's triality principle based on the extension of Chevalley product, between semispinor spaces and even subspaces of the extended exterior algebra over Euclidean space $\mathbb{R}^3$. The pure spinor formalism and the framework of Clifford algebras are used, in order to provide the necessary tools to introduce the Poincaré superalgebra where all the operators in space and superspace are constructed via pure spinors in $\mathbb{R}^3$ and the interaction principle, that generalizes the SO(8) triality principle.

Using the Campbell-Magaard theorem we show that any analytic spacetime can be locally embedded into the Cauchy development of legitimate initial data for the five dimensional vacuum Einstein equations. The embedding presents the domain of dependence property and the Cauchy stability with respect to those initial data.

The correspondence between conformal covariant fields in Minkowski's space-time and isometric fields in the five dimensional anti-deSitter space-time is extended to a six-dimensional bulk space and its regular sub-manifolds, so as to include the analysis of evaporating Schwarzschild's black holes without loss of quantum unitarity.

Thermal corrections to the entropy of black holes in the Lovelock gravity are calculated. As the thermodynamic behavior of the black holes of this theory falls into two classes, the thermodynamic quantities are computed in each case. Finally, the logarithmic prefactors are obtained in two different limits.

We find high overtones of the Dirac quasi-normal (QN) spectrum of a Schwarzschild black hole (Sbh), by Leaver's method. At high overtones, the spacing of the imaginary part of the QN spectrum is equidistant (Im omegan+1- Im omegan = i/8M , where M is the black hole mass). This can also be analytically obtained by means of a Born approximation. At high overtones, the real part of omegan goes to zero. Finally, we comment this result in the context of Hod's conjecture on highly damped QNMs and the area spectrum of (quantum) black holes.

We discuss the coupling of the electromagnetic field with a curved and torsioned Lyra manifold using the Duffin-Kemmer-Petiau theory. We will show how to obtain the equations of motion and energy-momentum and spin density tensors by means of the Schwinger Variational Principle.

I discuss the use the weak gravitational lensing effect to study the mass distribution and dynamical state of a sample of 24 X-ray luminous clusters of galaxies. By comparing the mass and light distributions of the clusters it is found that their mass centers, for the majority of the clusters, is consistent with the positions of optical centers. Some clusters present significant mass substructures which generally have optical counterparts. At least in one cluster (Abell 1451), it is detected a mass substructure without an obvious luminous counterpart. Clusters with intra-cluster gas colder than 8 keV show a good agreement between the different mass determinations, but clusters with gas hotter than 8 keV present weak lensing masses smaller than those inferred by the other methods and therefore have been diagnosed to be out of equilibrium.

Using X-ray observation we have obtained the deprojected gas density and temperature profiles for a sample of cluster of galaxies. We show that cool-core clusters, which are expected to be the largest relaxed structures in the universe, have central steep mass density profiles, similar to the cold dark matter density profiles resulting from cosmological N-body simulation. We will present detailed results for two clusters, Abell 85 and 586.

More than a dozen binary star systems hosting stellar-mass black holes have been discovered in our galaxy. Some of them eject collimated relativistic jets with apparent velocities larger than the light speed. These objects have been named microquasars thanks to their similarity with the distant quasars or active nuclei of galaxies that host supermassive black holes. We have recently proposed that the large scale superluminal ejections observed in the microquasars (e.g., GRS 1915+105 source) during radio flare events are produced by violent magnetic reconnection episodes in the accretion disk that surrounds the central source, a ten-solar-mass black hole (de Gouveia Dal Pino and Lazarian 2005). The process occurs when a large-scale magnetic field is established by a turbulent dynamo in the inner disk region with a ratio between the gas+radiation and the magnetic pressures beta ~ 1. During this process, substantial angular momentum is removed from the disk by the wind generated by the vertical magnetic flux therefore increasing the disk mass accretion to a value near (but below) the critical Eddington limit. Part of the magnetic energy released by reconnection heats the coronal gas above the disk that produces a steep, soft X-ray spectrum with luminosity consistent with observations. The remaining magnetic energy released goes to accelerate the particles to relativistic velocities (v ~ vA ~ c, where vA is the Alfvén speed) in the reconnection site through first-order Fermi processes. For the first time we have examined the Fermi process within the reconnection zone and found that a power-law electron distribution is produced N(E) <FONT FACE=Symbol>µ</FONT> E-alphaE, with alphaE = 5/2, and a corresponding synchrotron radio power-law spectrum with a spectral index which is compatible with that observed during the flares (Snu <FONT FACE=Symbol>µ n</FONT>-0.75), though a standard Fermi process behind shocks that develop just above the reconnection site is also possible. The possibility that the ejection mechanism of relativistic blobs induced by magnetic reconnection can be applied to all classes of black hole-relativisitc jet systems, from microquasars to quasars and active galactic nuclei, is addressed here.

Although we do not observe directly black holes in the Universe, their presence has been inferred in several astrophysical systems, from galactic to extragalactic scales. In this work, we will restrict our focus in the possible signatures of the presence of Kerr black holes in active galactic nuclei, one of the most powerful sources in the Universe. Particularly, we will discuss how jet/accretion disc precession and their directional stability can be used to trace the accretion disc properties as well as the black hole spin in the Seyfert galaxy NGC 1068.

The quality of supernova data will dramatically increase in the next few years by new experiments that will add high-redshift supernova to the currently known ones. In order to use this new data to discriminate between different dark energy models, the statefinder diagnostic was suggested [1] and investigated by Alam et al.[3] in the light of the proposed SuperNova Acceleration Probe (SNAP) satellite. By making use of the same procedure presented by these authors, we compare their analyzes with ours, which shows a more realistic supernovae redshift distribution and do not assume that the intercept is known. We also analyzed the behavior of the statefinder pair {r,s} and the alternative pair {s,q} in the presence of offset errors.

We review observations and gravitational lensing theory related to the magnification of background QSOs by intervening overdensities, and the induced cross-correlation between sources and foreground galaxies. We pay special attention to simulations, and present some preliminary results from high resolution cluster simulations, which show the role of the halo core and substructure on non-linear magnification. For massive clusters, deviations from the weak gravitational lensing regime are significant on arcmin scales and bellow. The accumulated knowledge in the field already shows that gravitational lensing magnification is an important astrophysical and cosmological tool.

Observations show that the Cosmic Microwave Background (CMB) contains tiny variations at the 10-5 level around its black-body equilibrium temperature. The detection of these temperature f luctuations provides to modern Cosmology evidence for the existence of primordial density perturbations that seeded all the structures presently observed. The vast majority of the cosmological information is contained in the 2-point temperature function, which measures the angular correlation of these temperature fluctuations distributed on the celestial sphere. Here we study such angular correlations using a recently introduced statistic-geometrical method. Moreover, we use Monte Carlo simulated CMB temperature maps to show the equivalence of this method with the 2-point temperature function (best known as the 2-Point Angular Correlation Function). We also investigate here the robustness of this new method under possible divisions of the original catalog-data in sub-catalogs. Finally, we show some applications of this new method to simple cases.