27 research outputs found
Electromagnetic wave propagation in general Kasner-like metrics
The curved spacetime Maxwell equations are applied to the anisotropically
expanding Kasner metrics. Using the application of vector identities we derive
2-order differential wave equations for the electromagnetic field
components; through this explicit derivation, we find that the
2-order wave equations are not uncoupled for the various
components (as previously assumed), but that gravitationally-induced coupling
between the electric and magnetic field components is generated directly by the
anisotropy of the expansion. The lack of such coupling terms in the wave
equations from several prior studies may indicate a generally incomplete
understanding of the evolution of electromagnetic energy in anisotropic
cosmologies. Uncoupling the field components requires the derivation of a
4-order wave equation, which we obtain for Kasner-like metrics
with generalized expansion/contraction rate indices. For the axisymmetric
Kasner case, , we obtain exact field solutions
(for general propagation wavevectors), half of which appear not to have been
found before in previous studies. For the other axisymmetric Kasner case,
, we use numerical methods to
demonstrate the explicit violation of the geometric optics approximation at
early times, showing the physical phase velocity of the wave to be inhibited
towards the initial singularity, with as .Comment: 32 pages, 1 figure; Further developments of research presented at the
22nd International Conference on General Relativity and Gravitatio
Cosmic Acceleration from Causal Backreaction with Recursive Nonlinearities
We revisit the causal backreaction paradigm, in which the need for Dark
Energy is eliminated via the generation of an apparent cosmic acceleration from
the causal flow of inhomogeneity information coming in towards each observer
from distant structure-forming regions. This second-generation formalism
incorporates "recursive nonlinearities": the process by which
already-established metric perturbations will then act to slow down all future
flows of inhomogeneity information. Here, the long-range effects of causal
backreaction are now damped, weakening its impact for models that were
previously best-fit cosmologies. Nevertheless, we find that causal backreaction
can be recovered as a replacement for Dark Energy via the adoption of larger
values for the dimensionless `strength' of the clustering evolution functions
being modeled -- a change justified by the hierarchical nature of clustering
and virialization in the universe, occurring on multiple cosmic length scales
simultaneously. With this, and with one new model parameter representing the
slowdown of clustering due to astrophysical feedback processes, an alternative
cosmic concordance can once again be achieved for a matter-only universe in
which the apparent acceleration is generated entirely by causal backreaction
effects. One drawback is a new degeneracy which broadens our predicted range
for the observed jerk parameter , thus removing what had
appeared to be a clear signature for distinguishing causal backreaction from
Cosmological Constant CDM. As for the long-term fate of the universe,
incorporating recursive nonlinearities appears to make the possibility of an
`eternal' acceleration due to causal backreaction far less likely; though this
does not take into account gravitational nonlinearities or the large-scale
breakdown of cosmological isotropy, effects not easily modeled within this
formalism.Comment: 53 pages, 7 figures, 3 tables. This paper is an advancement of
previous research on Causal Backreaction; the earlier work is available at
arXiv:1109.4686 and arXiv:1109.515
Evaluation of the Performance of Polished Mirror Surfaces for the TAMA Gravitational Wave Detector by Use of a Wave-Front Tracing Simulation
We evaluated the performance of polished mirror surfaces for the TAMA interferometric gravitational wave detector by comparing the experimental results with a wave-front tracing simulation. The TAMA mirror surfaces were polished to a roughness of a few nanometer rms. We confirmed that these polished mirrors do not limit the present TAMA sensitivity and that the target shot-noise sensitivity will be achieved with these mirrors, even if a power-recycling technique is introduced in the next stage of the TAMA
Simulating a dual-recycled gravitational wave interferometer with realistically imperfect optics
We simulate the performance of a gravitational wave interferometer in the
Dual Recycling (DR) configuration, as will be used for systems like
Advanced-LIGO. Our grid-based simulation program models complex interferometric
detectors with realistic optical deformations (e.g., fine-scale mirror surface
roughness). Broadband and Tuned DR are modeled here; the results are also
applied qualitatively to Resonant Sideband Extraction (RSE). Several beneficial
properties anticipated for DR detectors are investigated: signal response
tuning and narrowbanding, power loss reduction, and the reclamation of lost
power as useful light for signal detection. It is shown that these benefits
would be limited by large scattering losses in large (multi-kilometer) systems.
Furthermore, losses may be resonantly enhanced (particularly for RSE), if the
interferometer's modal resonance conditions are not well chosen. We therefore
make two principal recommendations for DR/RSE interferometers: the DR/RSE
cavity must be modally nondegenerate; and fabricated mirror surfaces and
coatings must be as smooth as is practically feasible.Comment: 50 pages, 11 figure