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M. La Camera

Publications and source records attributed to M. La Camera.

15 recordsLinked to original sources
arXiv2011

On thin-shell wormholes evolving in flat FRW spacetimes

We analize the stability of a class of thin-shell wormholes with spherical symmetry evolving in flat FRW spacetimes. The wormholes considered here are supported at the throat by a perfect fluid with equation of state $\mathcal{P}=wσ$ and have a physical radius equal to $aR$, where $a$ is a time-dependent function describing the dynamics of the throat and $R$ is the background scale factor. The study of wormhole stability is done by means of the stability analysis of dynamic systems.

gr-qc↗
arXiv2010

Time-dependent extra dimension and higher-dimensional modifications to the matter content in FRW spacetimes

In this work we suggest that higher-dimensional modifications to the matter content in FRW spacetimes can be obtained not only, as first considered by Ponce de Leon, referring to "moving" 4D hypersurfaces non-orthogonal to the time-dependent extra dimension of an embedding 5D manifold, but also referring to "fixed" 4D hypersurfaces orthogonal to a suitable scalar function which defines a static foliation of the 5D manifold and takes the role of the extra dimension in a suitable coordinate system. Results obtained in each approach crucially depend on the method used to identify the 4D metric of our brane universe from the 5D metric of the bulk manifold.

gr-qc↗
arXiv2008

Brane cosmology with R_(4) term in the bulk

We consider brane cosmology when the 4D Ricci scalar term is added to the 5D Einstein-Hilbert action and discuss the role that the addition of this term has on the brane-bulk system. The induced brane dynamics is shown to be the usual Einstein dynamics coupled to a modified energy-momentum tensor which is well defined once the 5D Einstein equations are solved in the bulk. The 5D Einstein equations valid everywhere in the bulk, but not in the brane, are projected on the brane. Then making use for the embedding of the brane in the bulk of the Israel junction conditions, modified by a source term coming from the addition of the intrinsic curvature scalar in the bulk action, it is possible to obtain the effective 4D Einstein equations on the brane consistent with the bulk geometry.

gr-qc↗
arXiv2008

On the classical confinement of test particles to a thin 3-brane in the absence of non-gravitational forces

The classical confinement condition of test particles to a brane universe in the absence of non-gravitational forces is transformed using the Hamilton-Jacobi formalism. The transformed condition provides a direct criterion for selecting in a cosmological scenario 5D bulk manifolds wherein it is possible to obtain confinement of trajectories to 4D hypersurfaces purely due to classical gravitational effects.

gr-qc↗
arXiv2003

Wormhole solutions in the Randall-Sundrum scenario

In the simplest form of the Randall-Sundrum model, we consider the metric generated by a static, spherically symmetric distribution of matter on the physical brane. The solution to the five-dimensional Einstein equations, obtained numerically, describes a wormhole geometry.

gr-qc↗
arXiv2002

Traceless stress-energy and traversable wormholes

A one-parameter family of static and spherically symmetric solutions to Einstein equations with a traceless energy-momentum tensor is found. When the nonzero parameter $β$ lies in the open interval $(0,1)$ one obtains traversable Lorentzian wormholes. One also obtains naked singularities when either $β< 0$ or $β> 1$ and the Schwarzschild black hole for $β= 1$.

gr-qc↗
arXiv2001

Brans-Dicke wormhole and space-time foam

We introduce, by means of the Brans-Dicke scalar field, space-time fluctuations at scale comparable to Planck length near the event horizon of a black hole and examine their dramatic effects.

hep-th↗
arXiv2000

Black hole horizon and space-time foam

We introduce, by means of the Brans-Dicke scalar field, space-time fluctuations at scale comparable to Planck length near the event horizon of a black hole and examine their dramatic effects.

gr-qc↗
arXiv2000

Schwarzschild metrics and quasi-universes

The exterior and interior Schwarzschild solutions are rewritten replacing the usual radial variable with an angular one. This allows to obtain some results otherwise less apparent or even hidden in other coordinate systems.

gr-qc↗
arXiv1999

Kerr-AdS and Kerr-dS solutions revisited

We reconsider the Kerr metric with cosmological term $Λ$ imposing the condition that the angular velocity $ω$ of the dragging of the inertial frames vanishes at spatial boundaries. Some properties of the extreme black holes in the revisited solutions are discussed.

gr-qc↗
arXiv1999

Black-body laws derived from a minimum knowledge of Physics

Starting from the knowledge of the four fundamental quantities length L, mass M, time T, absolute temperature $θ$ and accepting the validity of Gauss's law in all dimensions, we generalize, by the theory of physical dimensions, the expression of the Stephan-Boltzmann law and of the Planck's formula for the black-body radiation to a spacetime with one time and n spatial coordinates. In the particular case n=3 we shall recover the known results.

physics.gen-ph↗
arXiv1999

Cosmology with two compactification scales

We consider a (4+d)-dimensional spacetime broken up into a (4-n)-dimensional Minkowski spacetime (where n goes from 1 to 3) and a compact (n+d)-dimensional manifold. At the present time the n compactification radii are of the order of the Universe size, while the other d compactification radii are of the order of the Planck length.

gr-qc↗
arXiv1998

Geometrical features of (4+d) gravity

We obtain the vacuum spherical symmetric solutions for the gravitational sector of a (4+d)-dimensional Kaluza-Klein theory. In the various regions of parameter space, the solutions can describe either naked singularities or black-holes or wormholes. We also derive, by performing a conformal rescaling, the corresponding picture in the four-dimensional space-time.

gr-qc↗