1,720,977 research outputs found
de Sitter spacetime: effects of metric perturbations on geodesic motion
No full textGravitational perturbations of the de Sitter spacetime are investigated
using the Regge–Wheeler formalism. The set of perturbation equations is reduced
to a single second order differential equation of the Heun-type for both electric and
magnetic multipoles. The solution so obtained is used to study the deviation from an
initially radial geodesic due to the perturbation. The spectral properties of the perturbed
metric are also analyzed. Finally, gauge- and tetrad-invariant first-order massless perturbations
of any spin are explored following the approach of Teukolsky. The existence
of closed-form, i.e. Liouvillian, solutions to the radial part of the Teukolsky master
equation is discussed
Cylindrical gravitational waves: C-energy, super-energy and associated dynamical effects
No full textLate-time evolution of cosmological models with fluids obeying a Shan-Chen-like equation of state
No full textClassical as well as quantum features of the late-time evolution of cosmological models with fluids
obeying a Shan-Chen-like equation of state are studied. The latter is of the type p=weff(ρ)ρ and has been
used in previous works to describe, e.g., a possible scenario for the growth of the dark-energy content of the
present Universe. At the classical level, the fluid dynamics in a spatially flat Friedmann-Robertson-Walker
background implies the existence of two possible equilibrium solutions depending on the model parameters
associated with (asymptotic) finite pressure and energy density. We show that no future cosmological
singularity is developed during the evolution for this specific model. The corresponding quantum effects in
the late-time behavior of the system are also investigated within the framework of quantum geometrodynamics,
i.e., by solving the (minisuperspace) Wheeler-DeWitt equation in the Born-Oppenheimer
approximation, constructing wave packets and analyzing their behavior
Quadrupole effects on the motion of extended bodies in Schwarzschild spacetime
No full textThe motion of an extended body up to the quadrupolar structure is studied in the Schwarzschild background following Dixon's model and within certain restrictions (constant frame components for the spin and the quadrupole tensor, center of mass moving along a circular orbit, etc). We find a number of interesting situations in which deviations from the geodesic motion, due to the internal structure of the particle, can originate measurable effects. However, the standard clock effect for a pair of co/counter-rotating bodies spinning up/down is not modified by the quadrupolar structure of the particle. © 2008 IOP Publishing Ltd
Quadrupole effects on the motion of extended bodies in Kerr spacetime
No full textThe motion of a body endowed with a dipolar as well as a quadrupolar structure is investigated in the Kerr background according to the Dixon model, extending a previous analysis done in the Schwarzschild background. The full set of evolution equations is solved under the simplifying assumptions of constant frame components for both the spin and the quadrupole tensors and that the center of mass moves along an equatorial circular orbit, the total 4-momentum of the body being aligned with it. We find that the motion deviates from the geodesic one due to the internal structure of the body, leading to measurable effects. Corrections to the geodesic value of the orbital period of a close binary system orbiting the galactic center are discussed assuming that the galactic center is a Kerr supermassive black hole
Novel approach to the study of quantum effects in the early Universe
Full text linkWe develop a theoretical frame for the study of quantum gravitational waves. All the significant physical quantities can be formulated using Bogolubov transformations and the quadratic Hamiltonian operator corresponding to the classical version of a damped parametrically excited oscillator where the varying mass is replaced by the square cosmological scale factor. The destruction of quantum coherence due to the gravitational evolution in de Sitter scenarios is discussed
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