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## Theoretical studies
## IntroductionCurrently the most widely accepted theory of gravity is general relativity. This elegant theory of Einstein is a metric theory of gravity. This implies, in particular, that the distribution and motion of matter fields and the spacetime metric are in an intimate relation. While the matter fields determine the spacetime geometry via Einstein’s equations, the geometry is also involved in determining the evolution of matter fields via the pertinent field equations.In general relativity the truly dynamical sources can only be treated by either numerical or perturbative approaches. Whenever the gravitational field is weak and the motions are slow, the post-Newtonian approximation is applicable for the description of the motion of the sources. In all the other cases numerical approaches have to be applied. In our theoretical group both of these type of investigations are pursued.
## The post-Newtonian programThe most promising sources of gravitational radiation to be detected are compact binary systems composed of neutron stars and/or black holes in the last stage of their inspiral until the final plunge. To discuss the evolution of these systems to high precision the post-Newtonian (PN) approximation is a convenient method when the gravitational field is weak and the motion of the sources are slow. For the detailed description of the emitted gravitational radiation the PN approximation is matched with the post-Minkowskian multipolar expansion method in the near outer zone of the source. Our current results which are worked out up to 1.5 PN order should be of interest for the data analyzing processes. Thereby, our primary aim is to produce software injected fake GW signals for the Virgo detector as soon as it is possible. Assuming that the outcome of these investigations will be convincing enough in the succeeding period, we are going to work out the template banks fitting to the requirements of the CBC group of the Virgo collaboration. Following this, we are planning to extend the production of software injected fake GW signals relevant for binaries following parabolic or hyperbolic orbits yielding burst type signals. If the current template banks are lacking the sensitivity to these types of GW signals we are ready to provide the corresponding, possibly the first, template banks up to 1.5 PN order for the burst group.
## Numerical relativity programDuring the last couple of years we developed a numerical framework that is capable to investigate the evolution of generic dynamical systems in full 4-dimensional spacetimes. Our present numerical setting incorporates the highly advanced techniques of adaptive mesh refinement (AMR). In addition, in all of our numerical investigations distinguished attention has been paid to the precise description of energy transport processes, especially to determination of the part of the energy carried by various wave types.Our numerical facilities are suitable to carry out the study of the time evolution of various astrophysically interesting GW sources such as oscillating stars or stars that undergo a full gravitational collapse while a black hole is formed. We are also able to calculate the gravitational wave production, the form of the signals generated at the location of dynamical processes and the waveforms that can be observed in the distance. | ||||||||

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The RMKI Budapest Virgo Group
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-- GergelyDebreczeni - 19 Nov 2008 |

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