Fabris, Julio C., Jardim, Deborah F.
The dark energy component of the cosmic budget is represented by a self-interacting scalar field. The violation of the null energy condition is allowed. Hence, such component can also represent a...
Transient cosmic acceleration from interacting fluids (2009)
Fabris, Julio C., Fraga, Bernardo, Pinto-Neto, Nelson, Zimdahl, Winfried
Recent investigations seem to favor a cosmological dynamics according to which the accelerated expansion of the Universe may have already peaked and is now slowing down again \cite{sastaro}. As a...
Phantom Black Holes in Einstein-Maxwell-Dilaton Theory (2009)
Clement, Gerard, Fabris, Julio C., Rodrigues, Manuel Eleuterio
We obtain the general static, spherically symmetric solution for the Einstein-Maxwell-dilaton system in four dimensions with a phantom coupling for the dilaton and/or the Maxwell field. This leads to...
Quantum Particle Production at Sudden Singularities (2008)
Barrow, John D., Batista, Antonio B., Fabris, Julio C., Houndjo, Stephane
We investigate the effects of quantum particle production on a classical sudden singularity occurring at fine time in a Friedmann universe. We use an exact solution to describe an initially...
Big rip avoidance via black holes production (2008)
Fabris, Julio C., Pavon, Diego
We consider a cosmological scenario in which the expansion of the Universe is dominated by phantom dark energy and black holes which condense out of the latter component. The mass of black holes...
DM particles: how warm they can be? (2008)
Fabris, Julio C., Shapiro, Ilya L., Sobreira, Flavia
One of important questions concerning particles which compose the Dark Matter (DM) is their average speed. We consider the model of relativistic weakly interacting massive particles and try to impose...
Density Perturbations for Running Cosmological Constant (2006)
Fabris, Julio C., Shapiro, Ilya L., Sola, Joan
The dynamics of density and metric perturbations is investigated for the previously developed model where the decay of the vacuum energy into matter (or vice versa) is due to the renormalization...
Chaplygin gas with non-adiabatic pressure perturbations (2005)
Zimdahl, Winfried, Fabris, Julio C.
Perturbations in a Chaplygin gas, characterized by an equation of state $p = -A/\rho$, may acquire non-adiabatic contributions if spatial variations of the parameter $A$ are admitted. This feature is...
In the Search of Singularity-Free Cosmological Models in Effective Actions (2001)
Fundamental theories, like strings, supergravity, Kaluza-Klein, lead after dimensional reduction and a suitable choice of field configurations, to an effective action in four dimensions where gravity...
Scalar perturbations in a primordial inflationary scenario (2001)
Fabris, Julio C., Spindel, Philippe
We compute the spectral index for scalar perturbations generated in a primordial inflationary model. In this model, the transition of the inflationary phase to the radiative era is achieved through...
Quantum Cosmology in Scalar-Tensor Theories With Non Minimal Coupling (1999)
Fabris, Julio C., Pinto-Neto, Nelson, Velasco, A. F.
Quantization in the minisuperspace of non minimal scalar-tensor theories leads to a partial differential equation which is non separable. Through a conformal transformation we can recast the...
Singularities and Classical Limit in Quantum Cosmology (1997)
Colistete Jr., Roberto, Fabris, Julio C., Pinto-Neto, Nelson
Minisuperspace models derived from Kaluza-Klein theories and low energy string theory are studied. They are equivalent to one and two minimally coupled scalar fields. The general classical and...
Scalar Perturbations and Conformal Transformation (1996)
The non-minimal coupling of gravity to a scalar field can be transformed into a minimal coupling through a conformal transformation. We show how to connect the results of a perturbation calculation,...
Ring Wormholes in D-Dimensional Einstein and Dilaton Gravity (1996)
Bronnikov, Kirill A., Fabris, Julio C.
On the basis of exact solutions to the Einstein-Abelian gauge-dilaton equations in $D$-dimensional gravity, the properties of static axial configurations are discussed. Solutions free of curvature...