3,251 research outputs found
The fields of uniformly accelerated charges in de Sitter spacetime
The scalar and electromagnetic fields of charges uniformly accelerated in de
Sitter spacetime are constructed. They represent the generalization of the Born
solutions describing fields of two particles with hyperbolic motion in flat
spacetime. In the limit Lambda -> 0, the Born solutions are retrieved. Since in
the de Sitter universe the infinities I^+- are spacelike, the radiative
properties of the fields depend on the way in which a given point of I^+- is
approached. The fields must involve both retarded and advanced effects: Purely
retarded fields do not satisfy the constraints at the past infinity I^-.Comment: 5 pages, 3 figures, RevTeX; Slightly expanded version of the paper
published in Physical Review Letters. (The published version can be generated
from the same TeX source.); problem with the postscript fixe
The Gluonic Field of a Heavy Quark in Conformal Field Theories at Strong Coupling
We determine the gluonic field configuration sourced by a heavy quark
undergoing arbitrary motion in N=4 super-Yang-Mills at strong coupling and
large number of colors. More specifically, we compute the expectation value of
the operator tr[F^2+...] in the presence of such a quark, by means of the
AdS/CFT correspondence. Our results for this observable show that signals
propagate without temporal broadening, just as was found for the expectation
value of the energy density in recent work by Hatta et al. We attempt to shed
some additional light on the origin of this feature, and propose a different
interpretation for its physical significance. As an application of our general
results, we examine when the quark undergoes oscillatory motion,
uniform circular motion, and uniform acceleration. Via the AdS/CFT
correspondence, all of our results are pertinent to any conformal field theory
in 3+1 dimensions with a dual gravity formulation.Comment: 1+38 pages, 16 eps figures; v2: completed affiliation; v3: corrected
typo, version to appear in JHE
Primordial statistical anisotropy generated at the end of inflation
We present a new mechanism for generating primordial statistical anisotropy
of curvature perturbations. We introduce a vector field which has a non-minimal
kinetic term and couples with a waterfall field in hybrid inflation model. In
such a system, the vector field gives fluctuations of the end of inflation and
hence induces a subcomponent of curvature perturbations. Since the vector has a
preferred direction, the statistical anisotropy could appear in the
fluctuations. We present the explicit formula for the statistical anisotropy in
the primordial power spectrum and the bispectrum of curvature perturbations.
Interestingly, there is the possibility that the statistical anisotropy does
not appear in the power spectrum but does appear in the bispectrum. We also
find that the statistical anisotropy provides the shape dependence to the
bispectrum.Comment: 9 pages, This version supersedes the JCAP version. Minor revision
Accelerated sources in de Sitter spacetime and the insufficiency of retarded fields
The scalar and electromagnetic fields produced by the geodesic and uniformly
accelerated discrete charges in de Sitter spacetime are constructed by
employing the conformal relation between de Sitter and Minkowski space.
A special attention is paid to new effects arising in spacetimes which, like
de Sitter space, have spacelike conformal infinities. Under the presence of
particle and event horizons, purely retarded fields (appropriately defined)
become necessarily singular or even cannot be constructed at the "creation
light cones" -- future light cones of the "points" at which the sources "enter"
the universe. We construct smooth (outside the sources) fields involving both
retarded and advanced effects, and analyze the fields in detail in case of (i)
scalar monopoles, (ii) electromagnetic monopoles, and (iii) electromagnetic
rigid and geodesic dipoles.Comment: 36 pages, 5 figures, LaTex2e; minor misprints corrected, one
reference added and some terminology change
Level densities and thermodynamical properties of Pt and Au isotopes
The nuclear level densities of Pt and Au below the
neutron separation energy have been measured using transfer and scattering
reactions. All the level density distributions follow the constant-temperature
description. Each group of isotopes is characterized by the same temperature
above the energy threshold corresponding to the breaking of the first Cooper
pair. A constant entropy excess and is observed in
Pt and Au with respect to Pt and Au,
respectively, giving information on the available single-particle level space
for the last unpaired valence neutron. The breaking of nucleon Cooper pairs is
revealed by sequential peaks in the microcanonical caloric curve
Excitations in antiferromagnetic cores of superconducting vortices
We study excitations of the predicted antiferromagnetically ordered vortex
cores in the superconducting phase of the newly proposed SO(5) model of
strongly correlated electrons. Using experimental data from the literature we
show that the susceptibilities in the spin sector and the charge sector are
nearly equal, and likewise for the stiffnesses. In the case of strict equality
SO(5) symmetry is possible, and we find that if present the vortices give rise
to an enhanced neutron scattering cross section near the so called pi resonance
at 41 meV. In the case of broken SO(5) symmetry two effects are predicted.
Bound excitations can exist in the vortex cores with ``high'' excitation
energies slightly below 41 meV, and the massless Goldstone modes corresponding
to the antiferromagnetic ordering of the core can acquire a mass and show up as
core excitation with ``low'' excitation energies around 2 meV.Comment: 9 pages, RevTeX, including 3 postscript figures, submitted to Phys.
Rev. B, July 10, 199
The twin paradox and Mach's principle
The problem of absolute motion in the context of the twin paradox is
discussed. It is shown that the various versions of the clock paradox feature
some aspects which Mach might have been appreciated. However, the ultimate
cause of the behavior of the clocks must be attributed to the autonomous status
of spacetime, thereby proving the relational program advocated by Mach as
impracticable.Comment: Latex2e, 11 pages, 6 figures, 33 references, no tables. Accepted for
publication in The European Physical Journal PLUS (EPJ PLUS
Aspects of electrostatics in a weak gravitational field
Several features of electrostatics of point charged particles in a weak,
homogeneous, gravitational field are discussed using the Rindler metric to
model the gravitational field. Some previously known results are obtained by
simpler and more transparent procedures and are interpreted in an intuitive
manner. Specifically: (i) We show that the electrostatic potential of a charge
at rest in the Rindler frame is expressible as A_0=(q/l) where l is the affine
parameter distance along the null geodesic from the charge to the field point.
(ii) We obtain the sum of the electrostatic forces exerted by one charge on
another in the Rindler frame and discuss its interpretation. (iii) We show how
a purely electrostatic term in the Rindler frame appears as a radiation term in
the inertial frame. (In part, this arises because charges at rest in a weak
gravitational field possess additional weight due to their electrostatic
energy. This weight is proportional to the acceleration and falls inversely
with distance -- which are the usual characteristics of a radiation field.)
(iv) We also interpret the origin of the radiation reaction term by extending
our approach to include a slowly varying acceleration. Many of these results
might have possible extensions for the case of electrostatics in an arbitrary
static geometry. [Abridged Abstract]Comment: 26 pages; accepted for publication in Gen.Rel.Gra
Winterberg's conjectured breaking of the superluminal quantum correlations over large distances
We elaborate further on a hypothesis by Winterberg that turbulent
fluctuations of the zero point field may lead to a breakdown of the
superluminal quantum correlations over very large distances. A phenomenological
model that was proposed by Winterberg to estimate the transition scale of the
conjectured breakdown, does not lead to a distance that is large enough to be
agreeable with recent experiments. We consider, but rule out, the possibility
of a steeper slope in the energy spectrum of the turbulent fluctuations, due to
compressibility, as a possible mechanism that may lead to an increased
lower-bound for the transition scale. Instead, we argue that Winterberg
overestimated the intensity of the ZPF turbulent fluctuations. We calculate a
very generous corrected lower bound for the transition distance which is
consistent with current experiments.Comment: 7 pages, submitted to Int. J. Theor. Phy
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