22 research outputs found
Spinning strings, cosmic dislocations and chronology protection
A massless scalar field is quantized in the background of a spinning string
with cosmic dislocation. By increasing the spin density toward the dislocation
parameter, a region containing closed timelike curves (CTCs) eventually forms
around the defect. Correspondingly, the propagator tends to the ordinary cosmic
string propagator, leading therefore to a mean-square field fluctuation, which
remains well behaved throughout the process, unlike the vacuum expectation
value of the energy-momentum tensor, which diverges due to a subtle mechanism.
These results suggest that back reaction leads to the formation of a "horizon"
that protects from the appearance of CTCs.Comment: Published version, 4 pages, REVTeX
Testing the Newton second law in the regime of small accelerations
It has been pointed out that the Newtonian second law can be tested in the very small acceleration regime by using the combined movement of the Earth and Sun around the Galactic center of mass. It has been shown that there are only two brief intervals during the year in which the experiment can be completed, which correspond to only two specific spots on the Earth surface. An alternative experimental setup is presented to allow the measurement to be made on Earth at any location and at any time.It has been pointed out that the Newtonian second law can be tested in the very small acceleration regime by using the combined movement of the Earth and Sun around the Galactic center of mass. It has been shown that there are only two brief intervals during the year in which the experiment can be completed, which correspond to only two specific spots on the Earth surface. An alternative experimental setup is presented to allow the measurement to be made on Earth at any location and at any time
The Velocity of Gravitational Waves
We examine the propagation of gravitational waves in the new field theory of
gravitation recently proposed by Novello-De Lorenci-Luciane (NDL). This
examination is done on a solvable case corresponding to a spherically symmetric
static configuration. We show that in NDL theory the velocity of gravitational
waves is lower than light velocity. We point out some consequences of this
result and suggest a possible scenario for its verification
Electromagnetic wave propagation inside a material medium: an effective geometry interpretation
We present a method developed to deal with electromagnetic wave propagation
inside a material medium that reacts, in general, non-linearly to the field
strength. We work in the context of Maxwell' s theory in the low frequency
limit and obtain a geometrical representation of light paths for each case
presented. The isotropic case and artificial birefringence caused by an
external electric field are analyzed as an application of the formalism and the
effective geometry associated to the wave propagation is exhibited.Comment: REVTeX file, 6 pages. Version to appear in Phys. Lett.
On optical black holes in moving dielectrics
We study the optical paths of the light rays propagating inside a nonlinear
moving dielectric media. For the rapidly moving dielectrics we show the
existence of a distinguished surface which resembles, as far as the light
propagation is concerned, the event horizon of a black hole. Our analysis
clarifies the physical conditions under which electromagnetic analogues of the
gravitational black holes can eventually be obtained in laboratory.Comment: 5 pages, 2 figures, revtex
Light propagation in non linear electrodynamics
Working on the approximation of low frequency, we present the light cone
conditions for a class of theories constructed with the two gauge invariants of
the Maxwell field without making use of average over polarization states.
Different polarization states are thus identified describing birefringence
phenomena. We make an application of the formalism to the case of
Euler-Heisenberg effective Lagrangian and well know results are obtained.Comment: 3 pages, latex, no figures (to appear in Phys. Lett. B
An Analog Model for Quantum Lightcone Fluctuations in Nonlinear Optics
We propose an analog model for quantum gravity effects using nonlinear
dielectrics. Fluctuations of the spacetime lightcone are expected in quantum
gravity, leading to variations in the flight times of pulses. This effect can
also arise in a nonlinear material. We propose a model in which fluctuations of
a background electric field, such as that produced by a squeezed photon state,
can cause fluctuations in the effective lightcone for probe pulses. This leads
to a variation in flight times analogous to that in quantum gravity. We make
some numerical estimates which suggest that the effect might be large enough to
be observable.Comment: 15 pages, no figure
Eikonal Approximation to 5D Wave Equations as Geodesic Motion in a Curved 4D Spacetime
We first derive the relation between the eikonal approximation to the Maxwell
wave equations in an inhomogeneous anisotropic medium and geodesic motion in a
three dimensional Riemannian manifold using a method which identifies the
symplectic structure of the corresponding mechanics. We then apply an analogous
method to the five dimensional generalization of Maxwell theory required by the
gauge invariance of Stueckelberg's covariant classical and quantum dynamics to
demonstrate, in the eikonal approximation, the existence of geodesic motion for
the flow of mass in a four dimensional pseudo-Riemannian manifold. These
results provide a foundation for the geometrical optics of the five dimensional
radiation theory and establish a model in which there is mass flow along
geodesics. Finally we discuss the case of relativistic quantum theory in an
anisotropic medium as well. In this case the eikonal approximation to the
relativistic quantum mechanical current coincides with the geodesic flow
governed by the pseudo-Riemannian metric obtained from the eikonal
approximation to solutions of the Stueckelberg-Schr\"odinger equation. This
construction provides a model for an underlying quantum mechanical structure
for classical dynamical motion along geodesics on a pseudo-Riemannian manifold.
The locally symplectic structure which emerges is that of Stueckelberg's
covariant mechanics on this manifold.Comment: TeX file. 17 pages. Rewritten for clarit
On Slow Light as a Black Hole Analogue
Although slow light (electromagnetically induced transparency) would seem an
ideal medium in which to institute a ``dumb hole'' (black hole analog), it
suffers from a number of problems. We show that the high phase velocity in the
slow light regime ensures that the system cannot be used as an analog
displaying Hawking radiation. Even though an appropriately designed slow-light
set-up may simulate classical features of black holes -- such as horizon, mode
mixing, Bogoliubov coefficients, etc. -- it does not reproduce the related
quantum effects. PACS: 04.70.Dy, 04.80.-y, 42.50.Gy, 04.60.-m.Comment: 14 pages RevTeX, 5 figure
Nonsingular FRW cosmology and nonlinear electrodynamics
The possibility to avoid the cosmic initial singularity as a consequence of
nonlinear effects on the Maxwell eletromagnetic theory is discussed. For a flat
FRW geometry we derive the general nonsingular solution supported by a magnetic
field plus a cosmic fluid and a nonvanishing vacuum energy density. The
nonsingular behavior of solutions with a time-dependent -term are
also examined. As a general result, it is found that the functional dependence
of can uniquely be determined only if the magnetic field remains
constant. All these models are examples of bouncing universes which may exhibit
an inflationary dynamics driven by the nonlinear corrections of the magnetic
field.Comment: 20 pages, 7 figure