arXiv subjects
Publications and source records attributed to M. O. Calvao.
Several approaches to the matter creation problem in the context of cosmological models are summarily reviewed. A covariant formulation of the general relativistic imperfect simple fluid endowed with a process of matter creation is presented. By considering the standard big bang model, it is shown how the recent results of Prigogine et alii \cite{1} can be recovered and, at the same time their limits of validity are explicited.
We study the geometric effects of our galaxy's peculiar motion on the circles-in-the-sky. We show that the shape of these circles-in-the-sky remains circular, as detected by a local observer with arbitrary peculiar velocity. Explicit expressions for the radius and center position of such an observed circle-in-the-sky, as well as for the angular displacement of points on the circle, are derived. In general, a circle is detected as a circle of different radius, displaced relative to its original position, and centered at a point which does not correspond to its detected center in the comoving frame. Further, there is an angular displacement of points on the circles. These effects all arise from aberration of cosmic microwave background radiation, exhausting the purely geometric effects due to the peculiar motion of our galaxy, and are independent of both the large scale curvature of space and the expansion of the universe, since aberration is a purely local phenomenon. For a Lorentz-boosted observer with the speed of our entire galaxy, the maximum (detectable) changes in the angular radius of a circle, its maximum center displacement, as well as the maximum angular distortion are shown all to be of order $β=(v/c)$ radians. In particular, two back-to-back matching circles in a finite universe will have an upper bound of $2|β|$ in the variation of either their radii, the angular position of their centers, or the angular distribution of points.
We show that entropy perturbations can eliminate instabilities and oscillations, in the mass power spectrum of the quartessence Chaplygin models. Our results enlarge the current parameter space of models compatible with large scale structure and cosmic microwave background (CMB) observations.
We have run Monte Carlo simulations, for quasar clustering redshift distortions in the Two-Degree Field QSO Redshift Survey (2QZ), in order to elicit the power of redshift distortions (geometric Alcock-Paczynski and linear kinematic) to constrain the cosmological density and equation of state parameters, Omega_{m0}, Omega_{x0}, w, of a pressureless matter + dark energy model. It turns out that, for the cosmological constant case (w = -1), the test is especially sensitive to the difference Delta := Omega_{m0} - Omega_{Lambda 0}, whereas for the spatially flat case (k = 0), it is quite competitive with SNAP and DEEP, besides being complimentary to them; furthermore, we find that, whereas not knowing the actual value of the bias does not compromise the correct recovering of Delta, taking into account the linear velocity effect is absolutely relevant, all within the 2 sigma confidence level.
We show, through Monte Carlo simulations, that the Alcock-Paczynski test, as applied to quasar clustering, is a powerful tool to probe the cosmological density and equation of state parameters, Omega_{m0}, Omega_{x0} and w. By taking into account the effect of peculiar velocities upon the correlation function we obtain, for the Two-Degree Field QSO Redshift Survey (2QZ), the predicted confidence contours for the cosmological constant (w = -1) and spatially flat (Omega_{m0} + Omega_{x0}=1) cases. It turns out that, for w = -1, the test is especially sensitive to the difference Omega_{m0} - Omega_{Lambda 0}, thus being ideal to combine with CMB results. We also find out that, for the flat case, it is competitive with future supernova and galaxy number count tests, besides being complementary to them.
Redshift distortions, both geometrical and kinematical, of quasar clustering are simulated, for the Two-Degree Field QSO Redshift Survey (2QZ), showing that they are very effective to constrain the cosmological density and equation of state parameters, Omega_{m0}, Omega_{x0} and w. Particularly, it emerges that, for the cosmological constant case, the test is especially sensitive to the difference Omega_{m0} - Omega_{Lambda 0}, whereas, for the spatially flat case, it is quite competitive with future supernova and galaxy count tests, besides being complimentary to them.
The gravitational properties of the {\em only} static plane-symmetric vacuum solution of Einstein's field equations without cosmological term (Taub's solution, for brevity) are presented: some already known properties (geodesics, weak field limit and pertainment to the Schwarzschild family of spacetimes) are reviewed in a physically much more transparent way, as well as new results about its asymptotic structure, possible matchings and nature of the source are furnished. The main results point to the fact that the solution must be interpreted as representing the exterior gravitational field due to a {\em negative} mass distribution, confirming previous statements to that effect in the literature. Some analogies to Kasner's spatially homogeneous cosmological model are also referred to.