602 research outputs found
Weyl Card Diagrams and New S-brane Solutions of Gravity
We construct a new card diagram which accurately draws Weyl spacetimes and
represents their global spacetime structure, singularities, horizons and null
infinity. As examples we systematically discuss properties of a variety of
solutions including black holes as well as recent and new time-dependent
gravity solutions which fall under the S-brane class. The new time-dependent
Weyl solutions include S-dihole universes, infinite arrays and complexified
multi-rod solutions. Among the interesting features of these new solutions is
that they have near horizon scaling limits and describe the decay of unstable
objects.Comment: 78 pages, 32 figures. v2 added referenc
Recommended from our members
Unemployment in Greece: evidence from Greek regions
The purpose of the paper is to examine the nature of Greek unemployment allowing for cross-sectional dependence among Greek regions and for the presence of structural breaks. The paper contributes to the literature assessing the stochastic properties of Greek regional unemployment rates using recently developed and more powerful panel unit-root tests, such as the Lagrange Multiplier (LM) panel unit root test of Im et al.(2010), that allow for level and trend breaks, heterogeneity and cross-sectional dependence in the panel. The results show that in all cases, after taking into account the fact that regional unemployment rates in Greece are subject to a structural break both in mean and the slope of the series, the null hypothesis of a unit root is not rejected, indicating that the Greek regional unemployment series are non-stationary with the presence of a structural break
Shock waves and Birkhoff's theorem in Lovelock gravity
Spherically symmetric shock waves are shown to exist in Lovelock gravity.
They amount to a change of branch of the spherically symmetric solutions across
a null hypersurface. The implications of their existence for the status of
Birkhoff's theorem in the theory is discussed.Comment: 9 pages, no figures, clarifying changes made in the text of section
III and references adde
On the coupling between spinning particles and cosmological gravitational waves
The influence of spin in a system of classical particles on the propagation
of gravitational waves is analyzed in the cosmological context of primordial
thermal equilibrium. On a flat Friedmann-Robertson-Walker metric, when the
precession is neglected, there is no contribution due to the spin to the
distribution function of the particles. Adding a small tensor perturbation to
the background metric, we study if a coupling between gravitational waves and
spin exists that can modify the evolution of the distribution function, leading
to new terms in the anisotropic stress, and then to a new source for
gravitational waves. In the chosen gauge, the final result is that, in the
absence of other kind of perturbations, there is no coupling between spin and
gravitational waves.Comment: 4 pages, to appear in Proceedings of the II Stueckelberg Workshop -
Int. J. Mod. Phys.
Post-Newtonian gravitational radiation and equations of motion via direct integration of the relaxed Einstein equations. III. Radiation reaction for binary systems with spinning bodies
Using post-Newtonian equations of motion for fluid bodies that include
radiation-reaction terms at 2.5 and 3.5 post-Newtonian (PN) order (O[(v/c)^5]
and O[(v/c)^7] beyond Newtonian order), we derive the equations of motion for
binary systems with spinning bodies. In particular we determine the effects of
radiation-reaction coupled to spin-orbit effects on the two-body equations of
motion, and on the evolution of the spins. For a suitable definition of spin,
we reproduce the standard equations of motion and spin-precession at the first
post-Newtonian order. At 3.5PN order, we determine the spin-orbit induced
reaction effects on the orbital motion, but we find that radiation damping has
no effect on either the magnitude or the direction of the spins. Using the
equations of motion, we find that the loss of total energy and total angular
momentum induced by spin-orbit effects precisely balances the radiative flux of
those quantities calculated by Kidder et al. The equations of motion may be
useful for evolving inspiraling orbits of compact spinning binaries.Comment: 19 pages, small corrections, equivalent to published versio
Branes as BIons
A BIon may be defined as a finite energy solution of a non-linear field
theory with distributional sources. By contrast a soliton is usually defined to
have no sources. I show how harmonic coordinates map the exteriors of the
topologically and causally non-trivial spacetimes of extreme p-branes to BIonic
solutions of the Einstein equations in a topologically trivial spacetime in
which the combined gravitational and matter energy momentum is located on
distributional sources. As a consequence the tension of BPS p-branes is
classically unrenormalized. The result holds equally for spacetimes with
singularities and for those, like the M-5-brane, which are everywhere
singularity free.Comment: Latex, 9 pages, no figure
Extreme Mass Ratio Binary: Radiation reaction and gravitational waveform
For a successful detection of gravitational waves by LISA, it is essential to
construct theoretical waveforms in a reliable manner. We discuss gravitational
waves from an extreme mass ratio binary system which is expected to be a
promising target of the LISA project.
The extreme mass ratio binary is a binary system of a supermassive black hole
and a stellar mass compact object. As the supermassive black hole dominates the
gravitational field of the system, we suppose that the system might be well
approximated by a metric perturbation of a Kerr black hole. We discuss a recent
theoretical progress in calculating the waveforms from such a system.Comment: Classical and Quantum Gravity 22 (2005) S375-S379, Proceedings for
5th International LISA Symposiu
- …