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L. C. Garcia de Andrade

Publications and source records attributed to L. C. Garcia de Andrade.

At least 91 records · Page 5Linked to original sources
arXiv2000

Cosmological Density Perturbations in two fluid models on spin dominated inflation and the stability of Friedmann metric

A spinning fluid embedded in a space section flat Friedmann model is used to compute the cosmological density perturbation of the model.The spinning fluid obeys the Einstein-Cartan field equations while the Friedmann embedded model is assumed to obey the general the Friedmann equation in General Relativity.It is shown that at the early epochs of the Universe the spin-torsion contribution to the density perturbation on the matter phase dominates over the radiation perturbation.On the other hand at the present epochs of the Universe the spin-torsion contribution is more efficient in the matter perturbation.Stability of the Friedmann solution in Einstein-Cartan cosmology is also discussed.

astro-ph↗
arXiv2000

Extended Thermodynamics to Einstein-Cartan Cosmology

The thermodynamics is extented to spacetimes with spin-torsion density.Impplications to Einstein-Cartan-de Sitter inflationary phases are discussed.A relation between the spin-torsion density,entropy and temperature is presented.A lower limit for the radius of the Universe may be obtained from the spin-torsion density and the Planck lenght.

gr-qc↗
arXiv2000

Criteria for de Sitter inflation in Einstein-Cartan cosmology and COBE data

Criteria for the existence of de Sitter inflation with dilaton fields in four-dimensional space-times with torsion is discussed.The relation between matter density perturbation and the spin-density perturbation is stablished based on this criteria.From COBE data it is shown that there is a linear relationship between the spin-torsion density and temperature of the Universe for the case where matter density dominates the kinetic part of dilaton fields.

gr-qc↗
arXiv2000

Sachs-Wolfe effect in space-times with torsion

Cartan torsion contribution to Sachs-Wolfe effect in the inflationary phase of the Universe is discussed.From the COBE data of the microwave anisotropy is possible to compute the spin-density in the Universe as $10^{16}$ mks units.The spin-density fluctuations at the hadron era is shown to coincide with the anisotropy temperature fluctuations.

astro-ph↗
arXiv1999

On de Sitter gravitationally from the spin-torsion primordial density

Fluctuations on de Sitter solution of Einstein-Cartan field equations are obtained in terms of the matter density primordial density fluctuations and spin-torsion density and matter density fluctuations obtained from COBE data. Einstein-de Sitter solution is shown to be unstable even in the absence of torsion.The spin-torsion density fluctuation is simply computed from the Einstein-Cartan equations and from COBE data.

gr-qc↗
arXiv1999

On de Sitter deflationary cosmology from the spin-torsion primordial fluctuations and COBE data

Fluctuations on de Sitter solution of Einstein-Cartan field equations are obtained in terms of the matter density primordial density fluctuations and spin-torsion density and matter density fluctuations obtained from COBE data. Einstein-de Sitter solution is shown to be unstable even in the absence of torsion.The spin-torsion density fluctuation to generate a deflationary phase is computed from the COBE data.

gr-qc↗
arXiv1999

On Spin-driven inflation from fields in General Relativity and COBE data

Obukhov spin-driven inflation in General Relativity is extended to include inflaton fields.A de Sitter phase solution is obtained and new slow-rolling conditions for the spin potential are obtained.The spin potential reduces to Obukhov result at the present epoch of the Universe where the spin density is low with comparison to the Early Universe spin densities.A relation betwenn the spin density energy and the temperature fluctuation can be obtained which allow us to determine the spin density energy in terms of the COBE data for temperature fluctuations.

gr-qc↗
arXiv1999

Spin-torsion in Chaotic Inflation

The role of spin-torsion coupling to gravity is analyzed in the context of a model of chaotic inflation. The system of equations constructed from the Einstein-Cartan and inflaton field equations are studied and it is shown that spin-torsion interactions are effective only at the very first e-folds of inflation, becoming quickly negligible and, therefore, not affecting the standard inflationary scenario nor the density perturbations spectrum predictions.

gr-qc↗
arXiv1999

On non-Riemannian geometry of twisted nematic liquid crystals

A teleparallel geometrical description of the nematic phases of liquid crystals is proposed.In the case of the twisted geometry of nematics Cartan torsion is given by a spatial helical form which depends on the twist angle. Geodesics of a test particle around the teleparallel liquid crystal are given.

cond-mat↗
arXiv1999

Riemannian 2-D conical geometry of Heisenberg ferromagnets

An exact 2-dimensional conical Riemannian defect solution of 3-dimensional Euclidean Einstein equations of stresses and defects representing a shear-free Heisenberg ferromagnet is given.The system is equivalent to the Einstein equations in vacuum.Geodesics of magnetic monopoles around the ferromagnet are also investigated.

gr-qc↗
arXiv1999

Double cosmic walls in Teleparallel Gravity

An example is given of a plane topological torsion defect representing a cosmic wall double wall in teleparallel gravity.The parallel planar walls undergone a repulsive gravitational force due to Cartan torsion.This is the first example of a non-Riemannian double cosmic wall.It is shown that the walls oscillate with a speed that depends on torsion and on the surface density of the wall.Cartan torsion acts also as a damping force reducing the speed of oscillation when it is stronger.

gr-qc↗
arXiv1999

Telaparallel Textures

An example of a teleparallel texture is given by an appropriate choice of torsion components in the tetrad frame.In the light cone limit the metric is not globally Euclidean and the spherical angles depend on torsion similarly to what happens in cosmic string space-times.In this limit torsion produces a force which decays with $r^{-3}$.

gr-qc↗
arXiv1999

Non-Riemannian cosmic walls from gravitational collapse

Two classes of metrics obtained from non-Riemannian gravitational collapse are presented.The first is the Taub planar symmetric exact solutions of Einstein-Cartan field equations of gravity describing torsion walls which are obtained from gravitational collapse of time dependent perturbation of Riemannian Taub symmetric solutions of General Relativity.The second is a modification of the Vilenkin Riemannian planar wall which is obtained from a non-Riemannian planar distribution of spinning matter.

gr-qc↗
arXiv1999

On dilaton solutions of de Sitter inflation and primordial spin-torsion density fluctuations

Four classes of exact solutions of Einstein-Cartan dilatonic inflationary de Sitter cosmology are given.The first is obtained from the equation of state of massless dilaton instead of an unpolarized fermion fluid used previously by Gasperini.Repulsive gravity is found in the case where dilatons are constraint by the presence of spin-torsion effects.The second and third solutions represent respectively massive dilatons in the radiation era with the massive potential and torsion kinks and finally the dust of spinning particles.Primordial spin-density fluctuations are also computed based on Primordial fluctuations of temperature obtained from COBE data.The temperature fluctuation can also be computed from the nearly flat spectrum of the gravitational waves produced during inflation and by the result that the dilaton mass would be proportional to the Hubble constant.This result agrees with the COBE data.This idea is also used to compute the spin-torsion density in the inflation era.

gr-qc↗