2,336 research outputs found
Comment on ``Theorem for nonrotating singularity-free universes''
We show that Raychaudhuri's recently proposed theorem on nonrotating
universes cannot be used to rule out realistic singularity-free descriptions of
the universe, as suggested by him in PRL 80, 654 (1998).Comment: 1 page, to appear in Phys.Rev.Let
Phase space solutions in scalar-tensor cosmological models
An analysis of the solutions for the field equations of generalized
scalar-tensor theories of gravitation is performed through the study of the
geometry of the phase space and the stability of the solutions, with special
interest in the Brans-Dicke model. Particularly, we believe to be possible to
find suitable forms of the Brans-Dicke parameter omega and potential V of the
scalar field, using the dynamical systems approach, in such a way that they can
be fitted in the present observed scenario of the Universe.Comment: revtex, 2 pages, 4 eps figures, to appear in Brazilian Journal of
Physics (proceedings of the Conference 100 Years of Relativity, Sao Paulo,
Brazil, August 2005
Pseudoclassical Model of Spinning Particle with Anomalous Magnetic Momentum
A generalization of the pseudoclassical action of a spinning particle in the
presence of an anomalous magnetic momentum is given. The action is written in
reparametrization and supergauge invariant form. The Dirac quantization, based
on the Hamiltonian analyses of the model, leads to the Dirac-Pauli equation for
a particle with an anomalous magnetic momentum in an external electromagnetic
field. Due to the structure of first-class constraints in that case, the Dirac
quantization demands for consistency to take into account an operators ordering
problem.Comment: 9 pages, IFUSP/P-100
Near-horizon modes and self-adjoint extensions of the Schroedinger operator
We investigate the dynamics of scalar fields in the near-horizon exterior
region of a Schwarzschild black hole. We show that low-energy modes are
typically long-living and might be considered as being confined near the black
hole horizon. Such dynamics are effectively governed by a Schroedinger operator
with infinitely many self-adjoint extensions parameterized by , a
situation closely resembling the case of an ordinary free particle moving on a
semiaxis. Even though these different self-adjoint extensions lead to
equivalent scattering and thermal processes, a comparison with a simplified
model suggests a physical prescription to chose the pertinent self-adjoint
extensions. However, since all extensions are in principle physically
equivalent, they might be considered in equal footing for statistical analyses
of near-horizon modes around black holes. Analogous results hold for any
non-extremal, spherically symmetric, asymptotically flat black hole.Comment: 10 pages, 1 fig, contribution submitted to the volume "Classical and
Quantum Physics: Geometry, Dynamics and Control. (60 Years Alberto Ibort
Fest)" Springer (2018
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