210 research outputs found

### CAUSALITY, MEMORY ERASING AND DELAYED CHOICE EXPERIMENTS

Comment on [R.L. Ingraham, Phys. Rev. A 50, 4502 (1994)]. Ingraham suggested
``a delayed-choice experiment with partial, controllable memory erasing''. It
is shown that he cannot be right since his predictions contradict relativistic
causality. A subtle quantum effect which was overlooked by Ingraham is
explained.Comment: 4 pages, LaTe

### Shear and Vorticity in Inflationary Brans-Dicke Cosmology with Lambda-Term

We find a solution for exponential inflation in Brans-Dicke cosmology endowed
with a cosmological term, which includes time-varying shear and vorticity. We
find that the scalar field and the scale factor increase exponentialy while
shear, vorticity, energy density, cosmic pressure and the cosmological term
decay exponentialy for beta < 0, where beta is defined in the text.Comment: 8 pages including front one. Published by Astrophysics and Space
Scienc

### An interacting scalar field and the recent cosmic acceleration

In this paper it is shown that the Brans - Dicke scalar field itself can
serve the purpose of providing an early deceleration and a late time
acceleration of the universe without any need of quintessence field if one
considers an interaction, i.e, transfer of energy between the dark matter and
the Brans - Dicke scalar field.Comment: 10 pages, 2 figure

### Levi-Civita Effect in the polarizable vacuum (PV) representation of general relativity

The polarizable vacuum (PV) representation of general relativity (GR),
derived from a model by Dicke and related to the "TH-epsilon-mu" formalism used
in comparative studies of gravitational theories, provides for a compact
derivation of the Levi-Civita Effect (both magnetic and electric), herein
demonstrated.Comment: 8 page

### Mass loss by a scalar charge in an expanding universe

We study the phenomenon of mass loss by a scalar charge -- a point particle
that acts a source for a noninteracting scalar field -- in an expanding
universe. The charge is placed on comoving world lines of two cosmological
spacetimes: a de Sitter universe, and a spatially-flat, matter-dominated
universe. In both cases, we find that the particle's rest mass is not a
constant, but that it changes in response to the emission of monopole scalar
radiation by the particle. In de Sitter spacetime, the particle radiates all of
its mass within a finite proper time. In the matter-dominated cosmology, this
happens only if the charge of the particle is sufficiently large; for smaller
charges the particle first loses some of its mass, but then regains it all
eventually.Comment: 11 pages, RevTeX4, Accepted for Phys. Rev.

### Cooperative spontaneous emission in nonuniform media

The subject of this paper is modification of cooperative spontaneous emission
by a nonuniform medium, with nonuniform distributions of electromagnetic field.
A brief analyzis is presented and it is postulated, that if spontaneous
emission from an atom is strongly suppressed, cooperative emission with another
atom may be a preferred emission channel and counteract the suppression.Comment: The final publication is available at http://www.epj.or

### Kinetic Inflation in Stringy and Other Cosmologies

An inflationary epoch driven by the kinetic energy density in a dynamical
Planck mass is studied. In the conformally related Einstein frame it is easiest
to see the demands of successful inflation cannot be satisfied by kinetic
inflation alone. Viewed in the original Jordan-Brans-Dicke frame, the obstacle
is manifest as a kind of graceful exit problem and/or a kind of flatness
problem. These arguments indicate the weakness of only the simplest
formulation. {}From them can be gleaned directions toward successful kinetic
inflation.Comment: 26 pages, LaTeX, CITA-94-2

### WMAP constraints on scalar-tensor cosmology and the variation of the gravitational constant

We present observational constraints on a scalar-tensor gravity theory by
$\chi^2$ test for CMB anisotropy spectrum. We compare the WMAP temperature
power spectrum with the harmonic attractor model, in which the scalar field has
its harmonic effective potential with curvature $\beta$ in the Einstein
conformal frame and the theory relaxes toward Einstein gravity with time. We
found that the present value of the scalar coupling, i.e. the present level of
deviation from Einstein gravity $(\alpha_0^2)$, is bounded to be smaller than
$5\times 10^{-4-7\beta}$ ($2\sigma$), and $10^{-2-7\beta}$ ($4\sigma$) for $0<
\beta<0.45$. This constraint is much stronger than the bound from the solar
system experiments for large $\beta$ models, i.e., $\beta> 0.2$ and 0.3 in
$2\sigma$ and $4\sigma$ limits, respectively. Furthermore, within the framework
of this model, the variation of the gravitational constant at the recombination
epoch is constrained as $|G(z=z_{rec})-G_0|/G_0 < 0.05(2\sigma)$, and
$0.23(4\sigma)$.Comment: 7 page

### Shear and Vorticity in a Combined Einstein-Cartan-Brans-Dicke Inflationary Lambda-Universe

A combined BCDE (Brans-Dicke and Einstein-Cartan) theory with lambda-term is
developed through Raychaudhuri's equation, for inflationary scenario. It
involves a variable cosmological constant, which decreases with time, jointly
with energy density, cosmic pressure, shear, vorticity, and Hubble's parameter,
while the scale factor, total spin and scalar field increase exponentially. The
post-inflationary fluid resembles a perfect one, though total spin grows, but
the angular speed does not (Berman, 2007d). Keywords: Cosmology; Einstein;
Brans-Dicke; Cosmological term; Shear; Spin; Vorticity; Inflation;
Einstein-Cartan; Torsion. PACS: 04.20.-q ; 98.80.-k ; 98.80.Bp ; 98.80.JkComment: 8 pages including front one. Published versio

### 2d Stringy Black Holes and Varying Constants

Motivated by the recent interest on models with varying constants and whether
black hole physics can constrain such theories, two-dimensional charged stringy
black holes are considered. We exploit the role of two-dimensional stringy
black holes as toy models for exploring paradoxes which may lead to constrains
on a theory. A two-dimensional charged stringy black hole is investigated in
two different settings. Firstly, the two-dimensional black hole is treated as
an isolated object and secondly, it is contained in a thermal environment. In
both cases, it is shown that the temperature and the entropy of the
two-dimensional charged stringy black hole are decreased when its electric
charge is increased in time. By piecing together our results and previous ones,
we conclude that in the context of black hole thermodynamics one cannot derive
any model independent constraints for the varying constants. Therefore, it
seems that there aren't any varying constant theories that are out of favor
with black hole thermodynamics.Comment: 12 pages, LaTeX, to appear in JHE

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