6,644 research outputs found
The Gauge Fields and Ghosts in Rindler Space
We consider 2d Maxwell system defined on the Rindler space with metric
ds^2=\exp(2a\xi)\cdot(d\eta^2-d\xi^2) with the goal to study the dynamics of
the ghosts. We find an extra contribution to the vacuum energy in comparison
with Minkowski space time with metric ds^2= dt^2-dx^2. This extra contribution
can be traced to the unphysical degrees of freedom (in Minkowski space). The
technical reason for this effect to occur is the property of Bogolubov's
coefficients which mix the positive and negative frequencies modes. The
corresponding mixture can not be avoided because the projections to positive
-frequency modes with respect to Minkowski time t and positive -frequency modes
with respect to the Rindler observer's proper time \eta are not equivalent. The
exact cancellation of unphysical degrees of freedom which is maintained in
Minkowski space can not hold in the Rindler space. In BRST approach this effect
manifests itself as the presence of BRST charge density in L and R parts. An
inertial observer in Minkowski vacuum |0> observes a universe with no net BRST
charge only as a result of cancellation between the two. However, the Rindler
observers who do not ever have access to the entire space time would see a net
BRST charge. In this respect the effect resembles the Unruh effect. The effect
is infrared (IR) in nature, and sensitive to the horizon and/or boundaries. We
interpret the extra energy as the formation of the "ghost condensate" when the
ghost degrees of freedom can not propagate, but nevertheless do contribute to
the vacuum energy. Exact computations in this simple 2d model support the claim
made in [1] that the ghost contribution might be responsible for the observed
dark energy in 4d FLRW universe.Comment: Final version to appear in Phys. Rev. D. Comments on relation with
energy momentum computations and few new refs are adde
Interpretations of the Accelerating Universe
It is generally argued that the present cosmological observations support the
accelerating models of the universe, as driven by the cosmological constant or
`dark energy'. We argue here that an alternative model of the universe is
possible which explains the current observations of the universe. We
demonstrate this with a reinterpretation of the magnitude-redshift relation for
Type Ia supernovae, since this was the test that gave a spurt to the current
trend in favour of the cosmological constant.Comment: 12 pages including 2 figures, minor revision, references added, a
paragraph on the interpretation of the CMB anisotropy in the QSSC added in
conclusion, general results unchanged. To appear in the October 2002 issue of
the "Publications of the Astronmical Society of the Pacific
1+1+2 Electromagnetic perturbations on non-vacuum LRS class II space-times: Decoupling scalar and 2-vector harmonic amplitudes
We use the covariant and gauge-invariant 1+1+2 formalism of Clarkson and
Barrett \cite{Clarkson2003} to analyze electromagnetic (EM) perturbations on
non-vacuum {\it locally rotationally symmetric} (LRS) class II space-times.
Ultimately, we show how to derive six real decoupled equations governing the
total of six EM scalar and 2-vector harmonic amplitudes. Four of these are new,
and result from expanding the complex EM 2-vector which we defined in
\cite{Burston2007} in terms of EM 2-vector harmonic amplitudes. We are then
able to show that there are four precise combinations of the amplitudes that
decouple, two of these are polar perturbations whereas the remaining two are
axial. The remaining two decoupled equations are the generalized Regge-Wheeler
equations which were developed previously in \cite{Betschart2004}, and these
govern the two EM scalar harmonic amplitudes. However, our analysis generalizes
this by including a full description and classification of energy-momentum
sources, such as charges and currents.Comment: 9 page
Ringtail Disorder observed in Cotton Rats (Sigmodon hispidus)
This is the first description of ringtail syndrome in cotton rats (Sigmodon hispidus). The disorder was sporadically observed in a laboratory reared breeding colony. Incidence of tail lesions decreased after standardization of environmental humidityin the laboratory animal facility
Sum Rules for the Dirac Spectrum of the Schwinger Model
The inverse eigenvalues of the Dirac operator in the Schwinger model satisfy
the same Leutwyler-Smilga sum rules as in the case of QCD with one flavor. In
this paper we give a microscopic derivation of these sum rules in the sector of
arbitrary topological charge. We show that the sum rules can be obtained from
the clustering property of the scalar correlation functions. This argument also
holds for other theories with a mass gap and broken chiral symmetry such as QCD
with one flavor. For QCD with several flavors a modified clustering property is
derived from the low energy chiral Lagrangian. We also obtain sum rules for a
fixed external gauge field and show their relation with the bosonized version
of the Schwinger model. In the sector of topological charge the sum rules
are consistent with a shift of the Dirac spectrum away from zero by
average level spacings. This shift is also required to obtain a nonzero chiral
condensate in the massless limit. Finally, we discuss the Dirac spectrum for a
closely related two-dimensional theory for which the gauge field action is
quadratic in the the gauge fields. This theory of so called random Dirac
fermions has been discussed extensively in the context of the quantum Hall
effect and d-wave super-conductors.Comment: 41 pages, Late
Elastic cavitation, tube hollowing, and differential growth in plants and biological tissues
Elastic cavitation is a well-known physical process by which elastic materials under stress can open cavities. Usually, cavitation is induced by applied loads on the elastic body. However, growing materials may generate stresses in the absence of applied loads and could induce cavity opening. Here, we demonstrate the possibility of spontaneous growth-induced cavitation in elastic materials and consider the implications of this phenomenon to biological tissues and in particular to the problem of schizogenous aerenchyma formation
Akns Hierarchy, Self-Similarity, String Equations and the Grassmannian
In this paper the Galilean, scaling and translational self--similarity
conditions for the AKNS hierarchy are analysed geometrically in terms of the
infinite dimensional Grassmannian. The string equations found recently by
non--scaling limit analysis of the one--matrix model are shown to correspond to
the Galilean self--similarity condition for this hierarchy. We describe, in
terms of the initial data for the zero--curvature 1--form of the AKNS
hierarchy, the moduli space of these self--similar solutions in the Sato
Grassmannian. As a byproduct we characterize the points in the Segal--Wilson
Grassmannian corresponding to the Sachs rational solutions of the AKNS equation
and to the Nakamura--Hirota rational solutions of the NLS equation. An explicit
1--parameter family of Galilean self--similar solutions of the AKNS equation
and the associated solution to the NLS equation is determined.Comment: 25 pages in AMS-LaTe
Obtaining the spacetime metric from cosmological observations
Recent galaxy redshift surveys have brought in a large amount of accurate
cosmological data out to redshift 0.3, and future surveys are expected to
achieve a high degree of completeness out to a redshift exceeding 1.
Consequently, a numerical programme for determining the metric of the universe
from observational data will soon become practical; and thereby realise the
ultimate application of Einstein's equations. Apart from detailing the cosmic
geometry, this would allow us to verify and quantify homogeneity, rather than
assuming it, as has been necessary up to now, and to do that on a metric level,
and not merely at the mass distribution level. This paper is the beginning of a
project aimed at such a numerical implementation. The primary observational
data from our past light cone consists of galaxy redshifts, apparent
luminosities, angular diameters and number densities, together with source
evolution functions, absolute luminosities, true diameters and masses of
sources. Here we start with the simplest case, that of spherical symmetry and a
dust equation of state, and execute an algorithm that determines the unknown
metric functions from this data. We discuss the challenges of turning the
theoretical algorithm into a workable numerical procedure, particularly
addressing the origin and the maximum in the area distance. Our numerical
method is tested with several artificial data sets for homogeneous and
inhomogeneous models, successfully reproducing the original models. This
demonstrates the basic viability of such a scheme. Although current surveys
don't have sufficient completeness or accuracy, we expect this situation to
change in the near future, and in the meantime there are many refinements and
generalisations to be added.Comment: 26 pages, 10 figures. Minor changes to match the published versio
Gravitational Wave Emission from a Bounded Source: the Nonlinear Regime
We study the dynamics of a bounded gravitational collapsing configuration
emitting gravitational waves, where the exterior spacetime is described by
Robinson-Trautman geometries. The full nonlinear regime is examined by using
the Galerkin method that allows us to reduce the equations governing the
dynamics to a finite-dimensional dynamical system, after a proper truncation
procedure. Amongst the obtained results of the nonlinear evolution, one of the
most impressive is the fact that the distribution of the mass fraction
extracted by gravitational wave emission satisfies the distribution law of
nonextensive statistics and this result is independent of the initial
configurations considered.Comment: 3 page, 1 figure, proceedings of the X Marcel Grossmann Meeting 22-26
July, 2003, Rio de Janeir
Cosmological Perturbations of Quantum-Mechanical Origin and Anisotropy of the Microwave Background
Cosmological perturbations generated quantum-mechanically (as a particular
case, during inflation) possess statistical properties of squeezed quantum
states. The power spectra of the perturbations are modulated and the angular
distribution of the produced temperature fluctuations of the CMBR is quite
specific. An exact formula is derived for the angular correlation function of
the temperature fluctuations caused by squeezed gravitational waves. The
predicted angular pattern can, in principle, be revealed by the COBE-type
observations.Comment: 9 pages, WUGRAV-92-17 Accepted for Publication in Phys. Rev. Letters
(1993
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