Authors: Matthew Pitkin, James Clark, Martin A. Hendry, Ik Siong Heng, Chris Messenger, Jennifer Toher, Graham Woan
Date: 18 Feb 2008
Abstract: We open the discussion into how the Laser Interferometer Space Antenna (LISA) observations of supermassive black-hole (SMBH) mergers (in the mass range ~10ˆ6-10ˆ8 Msun) may be complementary to pulsar timing-based gravitational wave searches. We consider the toy model of determining pulsar distances by exploiting the fact that LISA SMBH inspiral observations can place tight parameter constraints on the signal present in pulsar timing observations. We also suggest, as a future path of research, the use of LISA ring-down observations from the most massive (>~ a few 10ˆ7 Msun) black-hole mergers, for which the inspiral stage will lie outside the LISA band, as both a trigger and constraint on searches within pulsar timing data for the inspiral stage of the merger.
Authors: Motoyuki Saijo, Yasufumi Kojima
Date: 15 Feb 2008
Abstract: We investigate the nonlinear behaviour of the dynamically unstable rotating star for the bar mode by three-dimensional hydrodynamics in Newtonian gravity. We find that an oscillation along the rotation axis is induced throughout the growth of the unstable bar mode, and that its characteristic frequency is twice as that of the bar mode, which oscillates mainly along the equatorial plane. A possibility to observe Faraday resonance in gravitational waves is demonstrated and discussed.
Authors: M. C. Washik, J. Healy, F. Herrmann, I. Hinder, D. M. Shoemaker, P. Laguna, R. A. Matzner
Date: 18 Feb 2008
Abstract: The spin of the final black hole in the coalescence of nonspinning black holes is determined by the ‘residual’ orbital angular momentum of the binary. This residual momentum consists of the orbital angular momentum that the binary is not able to shed in the process of merging. We study the angular momentum radiated, the spin of the final black hole and the gravitational bursts in a series of orbits ranging from almost direct infall to numerous orbits before infall that exhibit multiple bursts of radiation in the merger process. We show that the final black hole gets a maximum spin parameter $a/M_h \le 0.78$, and this maximum occurs for initial orbital angular momentum $L \approx Mˆ2_h$.
Authors: O.I. Chashchina, Z.K. Silagadze
Date: 18 Feb 2008
Abstract: This is a comment on the recent paper by G. S. Adkins and J. McDonnell ‘Orbital precession due to central-force perturbations’ published in Phys. Rev. D75 (2007), 082001 [arXiv:gr-qc/0702015]. We show that the main result of this paper, the formula for the precession of Keplerian orbits induced by central-force perturbations, can be obtained very simply by the use of Hamilton's vector.
Authors: Emanuele Berti, Vitor Cardoso
Date: 13 Feb 2008
Abstract: It has recently been suggested that scalar, Dirac and Rarita-Schwinger perturbations are related to thermodynamic phase transitions of charged (Reissner-Nordstr\"om) black holes. In this note we show that this result is probably a numerical coincidence, and that the conjectured correspondence does not straightforwardly generalize to other metrics, such as Kerr or Schwarzschild (anti-)de Sitter. Our calculations do not rule out a relation between dynamical and thermodynamical properties of black holes, but they suggest that such a relation is non-trivial.
Authors: Antoine Petiteau (APC), G. Auger (APC), H. Halloin (APC), O. Jeannin (APC), E. Plagnol (APC), Sophie Pireaux (ARTEMIS), Tania Regimbau (ARTEMIS), J.-Y. Vinet (ARTEMIS)
Date: 14 Feb 2008
Abstract: A new LISA simulator (LISACode) is presented. Its ambition is to achieve a new degree of sophistication allowing to map, as closely as possible, the impact of the different sub-systems on the measurements. LISACode is not a detailed simulator at the engineering level but rather a tool whose purpose is to bridge the gap between the basic principles of LISA and a future, sophisticated end-to-end simulator. This is achieved by introducing, in a realistic manner, most of the ingredients that will influence LISA's sensitivity as well as the application of TDI combinations. Many user-defined parameters allow the code to study different configurations of LISA thus helping to finalize the definition of the detector. Another important use of LISACode is in generating time series for data analysis developments.
Authors: Andres Rodriguez
Date: 10 Feb 2008
Abstract: LIGO observatories in Livingston, LA and Hanford, WA may detect gravitational waves emitted from coalescing binary systems composed of two compact objects. In order to detect compact binary coalescence (CBC) events, LIGO searches utilize matched filtering techniques. Matched filtering is the optimal detection strategy for stationary, Gaussian noise, however, LIGO noise is often non-stationary, non-Gaussian. Non-stationary noise result in an excess of false candidate events, commonly known as false alarms. This thesis develops the rˆ2 test to reduce the false alarm rate for LIGO CBC searches. Results of the search for primordial black hole binary systems (where each object has less than 1M_solar), in LIGO's Third Science Run (S3) is also presented.
Results of the rˆ2 test are shown for several LIGO CBC searches, including the binary neutron star searches in the Third and Fourth Science Runs (S3/S4), the S3/S4 primordial black hole searches, and the binary black hole search in the first three months of the Fifth Science Run (S5). The rˆ2 test significantly reduces the false alarm rate in these searches, while only falsely dismissing a small fraction of simulated events.
Authors: Luc Blanchet, Guillaume Faye, Bala R. Iyer, Siddhartha Sinha
Date: 9 Feb 2008
Abstract: The gravitational waveform (GWF) generated by inspiralling compact binaries moving in quasi-circular orbits is computed at the third post-Newtonian (3PN) approximation to general relativity. Our motivation is two-fold: (i) To provide accurate templates for the data analysis of gravitational wave inspiral signals in laser interferometric detectors; (ii) To provide the associated spin-weighted spherical harmonic decomposition to facilitate comparison and match of the high post-Newtonian prediction for the inspiral waveform to the numerically-generated waveforms for the merger and ringdown. This extension of the GWF by half a PN order (with respect to previous work at 2.5PN order) is based on the algorithm of the multipolar post-Minkowskian formalism, and mandates the computation of the relations between the radiative, canonical and source multipole moments for general sources at 3PN order. We also obtain the 3PN extension of the source multipole moments in the case of compact binaries, and compute the contributions of hereditary terms (tails, tails-of-tails and memory integrals) up to 3PN order. The end results are given for both the complete plus and cross polarizations and the separate spin-weighted spherical harmonic modes.
Authors: Michele Levi
Date: 11 Feb 2008
Abstract: We use recently proposed Kaluza-Klein (KK) reduction within an Effective Field Theory (EFT) approach to calculate the next to leading order gravitational spin-spin interaction between two spinning compact objects. It is proven here that to this order in this interaction the reduced KK action within the stationary approximation is sufficient for describing the gravitational interaction, and that it simplifies calculation substantially. We also find here that the gravito-magnetic vector field defined within the KK decomposition of the metric mostly dominates the mediation of the interaction. Our result coincides with that calculated with the ADM Hamiltonian formalism thus demonstrating clearly the equivalence of the ADM and the EFT approaches. Here we explain the origin of the seemingly discrepant but equivalent result previously derived within the EFT approach and fully reconcile the two approaches.
Authors: Thierry Appourchaux, Raymond Burston, Yanbei Chen, Michael Cruise, Hansjoerg Dittus, Bernard Foulon, Patrick Gill, Laurent Gizon, Hugh Klein, Sergei Klioner, Sergei Kopeikin, Hans Krueger, Claus Laemmerzahl, Alberto Lobo, Xinlian Luo, Helen Margolis, Wei-Tou Ni, Antonio Pulido Paton, Qiuhe Peng, Achim Peters, Ernst Rasel, Albrecht Ruediger, Etienne Samain, Hanns Selig, Diana Shaul, Timothy Sumner, Stephan Theil, Pierre Touboul, Slava Turyshev, Haitao Wang, Li Wang, Linqing Wen, Andreas Wicht, Ji Wu, Xiaomin Zhang, Cheng Zhao
Date: 5 Feb 2008
Abstract: ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD II is envisaged as a three-spacecraft mission which would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.
Authors: M. Alessandra Papa
Date: 7 Feb 2008
Abstract: I will review the most recent and interesting results from gravitational wave detection experiments, concentrating on recent results from the LIGO Scientific Collaboration (LSC). I will outline the methodologies utilized in the searches, explain what can be said in the case of a null result, what quantities may be constrained. I will compare these results with prior expectations and discuss their significance. As I go along I will outline the prospects for future improvements.
Authors: Bianca Dittrich, Simone Speziale
Date: 6 Feb 2008
Abstract: We introduce a modified Regge calculus for general relativity on a triangulated four dimensional Riemannian manifold where the fundamental variables are areas and a certain class of angles. These variables satisfy constraints which are local in the triangulation. We expect the formulation to have applications to classical discrete gravity and non-perturbative approaches to quantum gravity.
Authors: Rafael A. Porto, Ira Z. Rothstein
Date: 6 Feb 2008
Abstract: We use effective field theory techniques to compute the potentials due to spin-spin and spin-orbit effects, from which the spin(1)spin(2) contribution to the motion of spinning compact binaries to third Post-Newtonian (PN) order follow. We use a formalism which allows us to impose the spin supplementarity condition (SSC) in a canonical framework to all orders in the PN expansion. We explicitly show the equivalence with our previous results, obtained using the Newton-Wigner SSC at the level of the action for spin-spin and spin-orbit potentials reported in arXiv:gr-qc/0604099 and arXiv:0712.2032[gr-qc] respectively.
Authors: Emanuele Berti, Marta Volonteri
Date: 31 Jan 2008
Abstract: Using recent results from numerical relativity simulations of black hole mergers, we revisit previous studies of cosmological black hole spin evolution. We show that mergers are very unlikely to yield large spins, unless alignment of the spins of the merging holes with the orbital angular momentum is very efficient. If iron-line measurements and LISA observations of extreme mass-ratio inspirals (EMRIs) only yield dimensionless spins j>0.9, then prolonged accretion should be responsible for spin-up, and chaotic accretion scenarios would be very unlikely. If only a fraction of the whole population of low-redshift black holes spins rapidly, spin-alignment during binary mergers (rather than prolonged accretion) could be responsible for spin-ups.
Authors: Dorota Gondek-Rosinska (LUTH), Francois Limousin (LUTH)
Date: 31 Jan 2008
Abstract: We present calculations of the final phase of inspiral of irrotational strange star binaries. Two types of equation of state at zero temperature are used - the MIT bag model and the Dey et al. 1998 model of strange quark matter. We study the precoalescence stage within the Isenberg-Wilson-Mathews approximation of General Relativity using a multidomain spectral method. The gravitational-radiation driven evolution of the binary system is approximated by a sequence of quasi-equilibrium configurations at a fixed baryon number and with decreasing separation. We find that the innermost stable circular orbit (ISCO) is determined always by an orbital instability for binaries consisting of two stars built predominantly of strange quark matter independently on the total mass of a binary system and compactness parameter of each star. In contrast, for neutron stars described by baryonic equation of state without exotic phases the ISCO is given by the mass-shedding limit. The gravitational wave frequency at the ISCO, which marks the end of the inspiral phase, is always higher than 1.1kHz for equal masses irrotational strange quark stars with the total mass-energy of a binary system greater than $2 M_\odot$. We find that the dependence of the frequency of gravitational waves at the ISCO on the compactness parameter for the equal mass binaries can be described by the same simple analytical formulae for broad ranges of masses independently on a strange star model. Detailed comparisons with binary neutrons star models, as well as with the third order Post-Newtonian point-mass binaries are given. The difference in the phase, for two $1.35 M_\odot$ strange stars, between our numerical results and 3PN is $\sim 40 %$ for the last two orbits of inspiral.
© M. Vallisneri 2012 — last modified on 2010/01/29
Tantum in modicis, quantum in maximis