9,615 research outputs found
Algebraically special perturbations of the Schwarzschild solution in higher dimensions
We study algebraically special perturbations of a generalized Schwarzschild
solution in any number of dimensions. There are two motivations. First, to
learn whether there exist interesting higher-dimensional algebraically special
solutions beyond the known ones. Second, algebraically special perturbations
present an obstruction to the unique reconstruction of general metric
perturbations from gauge-invariant variables analogous to the Teukolsky scalars
and it is desirable to know the extent of this non-uniqueness. In four
dimensions, our results generalize those of Couch and Newman, who found
infinite families of time-dependent algebraically special perturbations. In
higher dimensions, we find that the only regular algebraically special
perturbations are those corresponding to deformations within the Myers-Perry
family. Our results are relevant for several inequivalent definitions of
"algebraically special".Comment: 23 pages, no figures. v2: references added; discussion improved;
matches published versio
False vacuum decay: effective one-loop action for pair creation of domain walls
An effective one-loop action built from the soliton field itself for the
two-dimensional (2D) problem of soliton pair creation is proposed. The action
consists of the usual mass term and a kinetic term in which the simple
derivative of the soliton field is replaced by a covariant derivative. In this
effective action the soliton charge is treated no longer as a topological
charge but as a Noether charge. Using this effective one-loop action, the
soliton-antisoliton pair production rate is calculated and one recovers Stone's
exponential factor and the prefactor of Kiselev, Selivanov and Voloshin. The
results are also valid straightforwardly to the problem of pair creation rate
of domain walls in dimensions greater than 2.Comment: 12 pages, Late
Fast and Slow solutions in General Relativity: The Initialization Procedure
We apply recent results in the theory of PDE, specifically in problems with
two different time scales, on Einstein's equations near their Newtonian limit.
The results imply a justification to Postnewtonian approximations when
initialization procedures to different orders are made on the initial data. We
determine up to what order initialization is needed in order to detect the
contribution to the quadrupole moment due to the slow motion of a massive body
as distinct from initial data contributions to fast solutions and prove that
such initialization is compatible with the constraint equations. Using the
results mentioned the first Postnewtonian equations and their solutions in
terms of Green functions are presented in order to indicate how to proceed in
calculations with this approach.Comment: 14 pages, Late
A Survey of the Spacecraft Line-Of-Sight Jitter Problem
Predicting, managing, controlling, and testing spacecraft Line-of-Sight (LoS) jit- ter due to on-board internal disturbance sources is a challenging multi- disciplinary systems engineering problem, especially for those observatories hosting extremely sensitive optical sensor payloads with stringent requirements on allowable LoS jitter. Some specific spacecraft jitter engineering challenges will be introduced and described in this survey paper. Illustrative examples of missions where dynamic interactions have to be addressed to satisfy demanding payload instrument LoS jitter requirements will be provided. Some lessons learned and a set of recommended rules of thumb are also presented to provide guidance for analysts on where to initiate and how to approach a new spacecraft jitter design problem. These experience-based spacecraft jitter lessons learned and rules of thumb are provided in the hope they can be leveraged on new space system development projects to help overcome unfamiliarity with previously identified jitter technical pitfalls and challenges
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