8 research outputs found
Classical and quantum quintessence cosmology
This paper implements the idea of considering the instantonic creation of
brane worlds whose five-dimensional bulk contains a negative cosmological
constant and a scalar quintessence field with time-dependent equation of state,
restricting to the case that the quintessence field couples minimally to
Hilbert-Einstein gravity. We construct an Euclidean formalism, both for the
four- and five-dimensional cases, singling out a Hamiltonian constraint that
depends on the parameter defining the quintessence state equation. Specializing
at several particular values of that parameter, we obtain solutions to the
constraint equation and analyse them both classically and quantum mechanically.
It is found that these solutions can represent either asymptotically anti-de
Sitter wormholes or pure anti-de Sitter spaces whose quantum states are
obtained by means of the Wheeler de Witt equation. Starting with the different
five-dimensional solutions, an instantonic procedure is applied to describe the
creation of geometrically equivalent inflating de Sitter branes whose quantum
states are also evaluated in some cases. We thus consider the quantum state of
the universe to be contributed by all the instantonic paths that correspond to
these particular brane worlds.Comment: 12 pages, RevTex, 1 figure incorporate
Unified Model for Dark Energy
A new model for the universe filled with a generalized Chaplygin fluid is
considered which unitarily describes as a single vacuum entity both a
quintessence scalar field and a cosmological constant, so unifying the notion
of dark energy. While the evolution of the universe filled with such a fluid
does not obviously contradict the present cosmic acceleration, the introduced
single dark-energy component, for equations of state with characteristic
parameter , behaves like an usual quintessence fluid with
constant equation of state at early high densities, and like a pure
cosmological constant at late cosmological times.Comment: 5 pages, some misprints corrected, a comment on the initial equation
of state inserted, one reference adde
Brane russian doll
It is shown that an (n-1)-dimensional inflating brane world instantonically
created from nothing can exist in the region beyond the Rindler horizon of the
Lorentzian spacetime associated with another inflating brane world in n
dimensions which is also instantonically created from nothing. Generalizing
this construction we obtain an unbounded from above tower of successive brane
worlds, each having one more dimension than the one which it nests and one less
dimension than the one which nests it.Comment: 10 pages, LaTe
Eternally accelerating universe without event horizon
Increasing astronomical evidence indicates that the expansion of the universe
is accelerating. By simply solving Einstein equations we show in this letter
that a wide class of generic quintessence models leading to eternal
acceleration is associated with spacetime static metrics which do not exhibit
future event horizons, and therefore do not pose the same problems for string
theory as asymptotic de Sitter space.Comment: 10 pages, LaTe
Active Faults in Iberia
43 pages, 9 figures, 1 tableThe distribution of active faults in the Iberian Peninsula is not homogeneous, being mainly present, but not only, in areas affected by the Alpine Orogeny. They are located in several regions: (1) The Iberian Massif, including Portugal, and Galicia and Cantabrian Mountains in the North, (2) The Pyrenees, (3) The NE of Iberia, (4) The Iberian Cordillera, and (5) The Betic Cordillera. The Pyrenees, the Iberian Cordillera, and particularly the Betic Cordillera are the most active regions. These faults have being considered active in a broad sense, that is to say, corresponding to faults that, at least, present movements during the Quaternary, not restricting them only to those presenting displacements during the late 10,000 years. Although important, faults situated offshore have not being included in the present reviewPeer Reviewe