Can noncommutativity resolve the Big-Bang singularity?

A possible way to resolve the singularities of general relativity is proposed based on the assumption that the description of space-time using commuting coordinates is not valid above a certain fundamental scale. Beyond that scale it is assumed that the space-time has noncommutative structure leading in turn to a resolution of the singularity. As a first attempt towards realizing the above programme a modification of the Kasner metric is constructed which is commutative only at large time scales. At small time scales, near the singularity, the commutation relations among the space coordinates diverge. We interpret this result as meaning that the singularity has been completely delocalized.Comment: Latex, 13 pages, 2 figures, accepted for publication in EPJ

Fungos em sementes de especies florestais com potencial agrossilvicultura no Parana.

Edição dos Anais do Congresso Florestal Brasileiro, 6., 1990, Campos do Jordão

Lista de las aves de la reserva Parque Luro, La Pampa

A survey was made of birds from Parque Luro Reserve in La Pampa province. The Iist of species was based on extensive census, point counts along border to lagoon and strip transect carried out between 1995 and 2001. The species registred were 146 belonging to 42 families. The result show that 55 percent is permanent resident and Tyrannidae, Emberizidae and Furnariidae were the families more abundant specifically. During the period of the study 66 species breed in the reserve, 77 percent were resident and 23 percent were summer resident. The Tyrannidae family contributed wiht the major number of nesting species and nest due to the abundance of nest corresponding to Serpophaga griseiceps, Pyrocephalus rubinus and Elaenia parvirostris. We recorded Molothrus bonariensis as parasite of Zonotrichia capensis and Mimus saturninus.Se realizó un relevamiento de las aves de la reserva Provincial Parque Luro (La Pampa, Argentina). La lista de especies se elaboró en base a observaciones extensivas sobre recorridos preestablecidos, puntos de observación a orillas de los cuerpos de agua y transectas de faja realizados durante los años 1995 a 2001. Se identificaron 146 especies pertenecientes a 42 familias. Los resultados indican que la ornitocenosis estuvo compuesta principalmente por especies residentes. Las familias mejor representadás desde el punto de vista específico fueron los Tyrannidae, Furnariidae y Emberizidae. Durante el período de estudio nidificaron en el área 66 especies, 77 % fueron residentes y 23% residentes estivales. La familia Tyrannidae fue la que aportó el mayor número de especies nidificantes y nidos, debido esto último a la abundancia de Serpophaga griseiceps, Pyrocephalus rubinus y Elaenia parvirostris. Se registró a Molothrus bonariensis como parásita de Zonotrichia capensis y Mimus saturninus

Noncommutative Geometry and Cosmology

We study some consequences of noncommutativity to homogeneous cosmologies by introducing a deformation of the commutation relation between the minisuperspace variables. The investigation is carried out for the Kantowski-Sachs model by means of a comparative study of the universe evolution in four different scenarios: the classical commutative, classical noncommutative, quantum commutative, and quantum noncommutative. The comparison is rendered transparent by the use of the Bohmian formalism of quantum trajectories. As a result of our analysis, we found that noncommutativity can modify significantly the universe evolution, but cannot alter its singular behavior in the classical context. Quantum effects, on the other hand, can originate non-singular periodic universes in both commutative and noncommutative cases. The quantum noncommutative model is shown to present interesting properties, as the capability to give rise to non-trivial dynamics in situations where its commutative counterpart is necessarily static.Comment: 22 pages, 5 figures, substantial changes in the presentation, results are the same, to appear in Physical Review

Noncommutative Conformally Coupled Scalar Field Cosmology and its Commutative Counterpart

We study the implications of a noncommutative geometry of the minisuperspace variables for the FRW universe with a conformally coupled scalar field. The investigation is carried out by means of a comparative study of the universe evolution in four different scenarios: classical commutative, classical noncommutative, quantum commutative, and quantum noncommutative, the last two employing the Bohmian formalism of quantum trajectories. The role of noncommutativity is discussed by drawing a parallel between its realizations in two possible frameworks for physical interpretation: the NC-frame, where it is manifest in the universe degrees of freedom, and in the C-frame, where it is manifest through theta-dependent terms in the Hamiltonian. As a result of our comparative analysis, we find that noncommutative geometry can remove singularities in the classical context for sufficiently large values of theta. Moreover, under special conditions, the classical noncommutative model can admit bouncing solutions characteristic of the commutative quantum FRW universe. In the quantum context, we find non-singular universe solutions containing bounces or being periodic in the quantum commutative model. When noncommutativity effects are turned on in the quantum scenario, they can introduce significant modifications that change the singular behavior of the universe solutions or that render them dynamical whenever they are static in the commutative case. The effects of noncommutativity are completely specified only when one of the frames for its realization is adopted as the physical one. Non-singular solutions in the NC-frame can be mapped into singular ones in the C-frame.Comment: explanations added, references include