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Search Results: 1 - 10 of 7176 matches for " Franco Fiorini "
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Nonsingular Promises from Born-Infeld Gravity
Franco Fiorini
Physics , 2013,
Abstract: Born-Infeld determinantal gravity formulated in Weitzenbock spacetime is discussed in the context of Friedmann-Robertson-Walker (FRW) cosmologies. It is shown how the standard model big bang singularity is absent in certain spatially flat FRW spacetimes, where the high energy regime is characterized by a de Sitter inflationary stage of geometrical character, i.e., without the presence of the inflaton field. This taming of the initial singularity is also achieved for some spatially curved FRW manifolds where the singularity is replaced by a de Sitter stage or a big bounce of the scale factor depending on certain combinations of free parameters appearing in the action. Unlike other Born-Infeld-like theories in vogue, the one here presented is also capable of deforming vacuum general relativistic solutions.
On Born-Infeld Gravity in Weitzenbock spacetime
Rafael Ferraro,Franco Fiorini
Physics , 2008, DOI: 10.1103/PhysRevD.78.124019
Abstract: Using the Teleparallel Equivalent of General Relativity formulated in Weitzenb\"{o}ck spacetime, we thoroughly explore a kind of Born-Infeld regular gravity leading to second order field equations for the vielbein components. We explicitly solve the equations of motion for two examples: the extended BTZ black hole, which results to exist even if the cosmological constant is positive, and a cosmological model with matter, where the scale factor results to be well behaved, giving so a singularity-free solution.
A type of Born-Infeld regular gravity and its cosmological consequences
Franco Fiorini,Rafael Ferraro
Physics , 2009, DOI: 10.1142/S0217751X09045236
Abstract: Born-Infeld deformation strategy to smooth theories having divergent solutions is applied to the teleparallel equivalent of General Relativity. The equivalence between teleparallelism and General Relativity is exploited to obtain a deformed theory of gravity based on second order differential equations, since teleparallel Lagrangian is built just from first derivatives of the vierbein. We show that Born-Infeld teleparallelism cures the initial singularity in a spatially flat FRW universe; moreover, it provides a natural inflationary stage without resorting to an inflaton field. The Born-Infeld parameter bounds the dynamics of Hubble parameter H(t) and establishes a maximum attainable spacetime curvature.
Spherically symmetric static spacetimes in vacuum f(T) gravity
Rafael Ferraro,Franco Fiorini
Physics , 2011, DOI: 10.1103/PhysRevD.84.083518
Abstract: We show that Schwarzschild geometry remains as a vacuum solution for those four-dimensional f(T) gravitational theories behaving as ultraviolet deformations of general relativity. In the gentler context of three-dimensional gravity, we also find that the infrared-deformed f(T) gravities, like the ones used to describe the late cosmic speed up of the Universe, have as the circularly symmetric vacuum solution a Deser-de Sitter or a BTZ-like spacetime with an effective cosmological constant depending on the infrared scale present in the function f(T).
Cosmological frames for theories with absolute parallelism
Rafael Ferraro,Franco Fiorini
Physics , 2011, DOI: 10.1142/S2010194511001310
Abstract: The vierbein (tetrad) fields for closed and open Friedmann-Robertson-Walker cosmologies are hard to work out in most of the theories featuring absolute parallelism. The difficulty is traced in the fact that these theories are not invariant under local Lorentz transformations of the vierbein. We illustrate this issue in the framework of f(T) theories and Born-Infeld determinantal gravity. In particular, we show that the early Universe as described by the Born-Infeld scheme is singularity free and naturally inflationary as a consequence of the very nature of Born-Infeld gravitational action.
Born-Infeld Determinantal gravity and the taming of the conical singularity in 3-dimensional spacetime
Rafael Ferraro,Franco Fiorini
Physics , 2009, DOI: 10.1016/j.physletb.2010.07.040
Abstract: In the context of Born-Infeld \emph{determinantal} gravity formulated in a n-dimensional spacetime with absolute parallelism, we found an exact 3-dimensional \emph{vacuum} circular symmetric solution without cosmological constant consisting in a rotating spacetime with non singular behavior. The space behaves at infinity as the conical geometry typical of 3-dimensional General Relativity without cosmological constant. However, the solution has no conical singularity because the space ends at a minimal circle that no freely falling particle can ever reach in a finite proper time. The space is curved, but no divergences happen since the curvature invariants vanish at both asymptotic limits. Remarkably, this very mechanism also forbids the existence of closed timelike curves in such a spacetime.
Modified teleparallel gravity: inflation without inflaton
Rafael Ferraro,Franco Fiorini
Physics , 2006, DOI: 10.1103/PhysRevD.75.084031
Abstract: Born-Infeld strategy to smooth theories having divergent solutions is applied to teleparallel equivalent of General Relativity. Differing from other theories of modified gravity, modified teleparallelism leads to second order equations, since teleparallel Lagrangian only contains first derivatives of the vierbein. We show that Born-Infeld-modified teleparallelism solves the particle horizon problem in a spatially flat FRW universe by providing an initial exponential expansion without resorting to an inflaton field.
Non trivial frames for f(T) theories of gravity and beyond
Rafael Ferraro,Franco Fiorini
Physics , 2011, DOI: 10.1016/j.physletb.2011.06.049
Abstract: Some conceptual issues concerning $f(T)$ theories --a family of modified gravity theories based on absolute parallelism-- are analyzed. Due to the lack of local Lorentz invariance, the autoparallel frames satisfying the field equations are evasive to an \emph{a priori} physical understanding. We exemplify this point by working out the vierbein (tetrad) fields for closed and open Friedmann-Robertson-Walker cosmologies.
The regular cosmic string in Born-Infeld gravity
Rafael Ferraro,Franco Fiorini
Physics , 2010, DOI: 10.1088/1742-6596/314/1/012114
Abstract: It is shown that Born-Infeld gravity --a high energy deformation of Einstein gravity-- removes the singularities of a cosmic string. The respective vacuum solution results to be free of conical singularity and closed timelike curves. The space ends at a minimal circle where the curvature invariants vanish; but this circle cannot be reached in a finite proper time.
Compact extra dimensions in cosmologies with f(T) structure
Franco Fiorini,P. A. Gonzalez,Yerko Vasquez
Physics , 2013, DOI: 10.1103/PhysRevD.89.024028
Abstract: The presence of compact extra dimensions in cosmological scenarios in the context of f(T)-like gravities is discussed. For the case of toroidal compactifications, the analysis is performed in an arbitrary number of extra dimensions. Spherical topologies for the extra dimensions are then carefully studied in six and seven spacetime dimensions, where the proper vielbein fields responsible for the parallelization process are found.
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