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## VESF Postdoctoral Fellowship (EGO-DIR-128-2008)
## Background of research subject
## Research program and expected results:The 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 system. In the main stream investigations of the post-Newtonian description of binary systems the principal aim was to achieve the highest possible PN; currently 3.5 PN order ; level since then the frequency of the associated GW signals is supposed to be high enough to be relevant for the ground-based interferometric GW detectors. This required the use of a great number of simplifying assumptions concerning the underlying binary system. For instance in most of the cases the investigations were restricted to the case of circular orbits and the spin-orbit, spin-spin and quadrupole-monopole interactions were completely neglected. During the last decade more and more investigations take into account these additional astrophysically important effects and the eccentricity of the orbits [1],[2]. There are important preliminary results concerning the full description of the motion of the binary [3], [4], nevertheless the equations of motion either are not solved or some of the above mentioned contributions are still missing. More than a decade ago an intensive study of the PN framework has been started under the leadership of Zoltán Perjés in our institute, at the KFKI Research Institute for Particle and Nuclear Physics. Our principal aim was to include all the astrophysically important effects in describing the motion of the binary and also to determine the created GW signals. Because these effects were missing from the former studies in our investigations we had to reproduce all the succeeding PN levels of corrections starting with the lowest order above the Newtonian. In the associated process we have given a new, detailed parametrization independent method in describing the motion of the binary system including the usual 1 PN corrections and spin-orbit contributions manifest themselves through spin precession, orbital precession and orbital frequency ; and to determine the and polarization states of the emitted waveform [5],[6],[7] up to 1.5 PN order while keeping all the terms relevant for compact binaries. Our results contain the explicit description of the motion including angular evolution and the analytic form of the polarization states with the use of the generalized true anomaly parametrization [8]. Following the steps given in the general method we have given time-dependent templates in the circular orbit limit. The associated results are currently written up for publication. These results justify the significance of the eccentricity of the orbits and the effects of the spin-orbit interaction. For instance, the importance of spin effects on the waveform can be seen at 1.5 PN order in the equal or nearly equal mass case which is supposed to be highly relevant for neutron star binaries. Since the non-spinning contributions are all multiplied by the difference of the masses of the objects, the spin-orbit interaction dominates the waveform at 1.5 PN order, in these particular cases. As opposed to this our first results demonstrate that in the general case the spin effects highly changes the characteristic properties of the waveforms even in the circular orbit special case from 1.5 PN order, although at lower orders these effects are definitely less significant. It is an important byproduct of the fact that the eccentricity of the orbits is also taken into account that higher harmonics of the waveforms appear in the analytic expressions. This effect enhances the probability of the detection of binary sources during the inspiralling era. The inclusion of the eccentricity is also supported by the fact that there has to be a significant fraction of the binaries, where the circularization of the orbits do not come to an end due to gravitational radiation in advance to the coalescence. Based on our present results the following three main research programs manifest themselves as the ones which can also be considered as natural continuation of our former investigations: - The most straightforward is to complete our research at 1.5 PN order. This work includes the detailed investigation of the waveforms, the evaluation of ready-to-use GW templates, the determination of the effects of the different dynamical and geometrical parameters on the waveforms. An additional, more ambitious goal is to provide, based on our theoretical model, a method which can be applied in data analyzing processes to determine the astrophysical parameters (masses, spins, etc.) of the sources by making use of the detected GW signals. Our analytic results could also be useful in providing analytic initial conditions for numerical simulations describing coalescence.
- The next reasonable step to do is the investigation of spin-spin and quadrupole-monopole interactions at 2 PN order. The first one is mainly important in the case of BH-BH and rapidly rotating BH-NS, NS-NS sources, and the second one is relevant in the case of slowly rotating NS-NS binaries. Perhaps the importance of these effects is underlined by the fact that the inclusion of spin-spin interaction is not compatible with the usual assumptions guaranteeing the circularization of the orbits [9].
- The investigation of binaries following parabolic or hyperbolic orbits is also very promising since they yield unique, non-periodic and presumably strong enough GW signals. As former investigations show [10], the event rate is higher than one per year at the frequency range of the Virgo detector. Although these binaries appear to be relevant for the operating GW observatories, very few sufficiently detailed investigations of these types of systems have been done. The theoretical description of these sources is in a preliminary state, i.e., the parametrization of the orbit is available up to 1 PN order [11], and the description of the waveform is only at the Newtonian level.
- C. Köenigsdöerffer, A. Gopakumar, Phys. Rev. D71, 024039 (2005).
- A. Gopakumar and B. I. Iyer, Phys. Rev. D65 084011 (2002).
- G. Faye, L. Blanchet, and A. Buonanno, Phys. Rev. D74, 104033 (2006).
- E. Racine, Phys. Rev. D78, 044021 (2008).
1 J. Majár and M. Vasúth, Phys. Rev. D74, 124007 (2006).
- M. Vasúth and J. Majár, IJMPA 22, 2405 (2007).
1 J. Majár and M. Vasúth, Phys. Rev. D77, 104005 (2008).
- L. Á. Gergely, Z. Keresztes, and B. Mikóczi, Astrophys.J.Suppl. 167, 286 (2006).
- L. E. Kidder, Phys.Rev. D52 821 (1995).
1 B. Kocsis, M. E. Gáspár and Sz. Márka, Astrophys. J. 648, 411 (2006).
- T. Damour and N. Deruelle, Annales de l’I.H.P A 43 no. 1, 107 (1985).
## Research environment
Such as group composition and experience, equipment:
## The schedule and milestones of the research program:
- Since we believe that our current results which are worked out up to 1.5 PN order will be found to be of sufficient interest for the data analyzing processes, our primary aim is to produce software injected fake GW signals 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. This part should be completed in 6 months after the start of the VESF program.
- Following this, as an immediate application of our former results, during the second half of the first year we are going 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.
- In parallel to these activities we shall also start to investigate the extendibility of our results up to 2 PN order.
2nd year:
- As a more theoretical starting at the beginning of the second year emphasis will be given to the work out of the full description of the dynamics of the selected binary systems. In parallel we also determine the produced gravitational waveforms up to 2 PN order.
- Based on these results we are going to upgrade the template banks produced during the first year of this research plan for both bounded and unbounded binary systems.
- Finally, if it will be possible we would like to make some progress in the investigation of radiation reaction effects at 2.5 PN order.
-- GergelyDebreczeni - 19 Jan 2009 |

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