[gr-qc/0610155] Radar ranging and Doppler tracking in post-Einsteinian metric theories of gravity

Authors: Marc-Thierry Jaekel (LPTENS), Serge Reynaud (LKB - Jussieu)

Date: Mon, 30 Oct 2006

Abstract: The study of post-Einsteinian metric extensions of general relativity (GR), which preserve the metric interpretation of gravity while considering metrics which may differ from that predicted by GR, is pushed one step further. We give a complete description of radar ranging and Doppler tracking in terms of the time delay affecting an electromagnetic signal travelling between the Earth and a remote probe. Results of previous publications concerning the Pioneer anomaly are corrected and an annually modulated anomaly is predicted besides the secular anomaly. Their correlation is shown to play an important role when extracting reliable information from Pioneer observations. The formalism developed here provides a basis for a quantitative analysis of the Pioneer data, in order to assess whether extended metric theories can be the appropriate description of gravity in the solar system.

abs pdf

Oct 31, 2006

0610155 (/preprints/gr-qc)
2006-10-31, 05:33 [edit]

[gr-qc/0610139] Accurate and efficient gravitational waveforms for certain galactic compact binaries

Authors: Manuel Tessmer, Achamveedu Gopakumar

Date: Fri, 27 Oct 2006

Abstract: Stellar-mass compact binaries in eccentric orbits are almost guaranteed sources of gravitational waves for Laser Interferometer Space Antenna. We present a prescription to compute accurate and efficient gravitational-wave polarizations associated with bound compact binaries of arbitrary eccentricity and mass ratio moving in slowly precessing orbits. We compare our approach with those existing in the literature and present its advantages.

abs pdf

Oct 30, 2006

0610139 (/preprints/gr-qc)
2006-10-30, 08:54 [edit]

[gr-qc/0610126] Binary black hole spectroscopy

Authors: Chris Van Den Broeck, Anand Sengupta

Date: Thu, 26 Oct 2006

Abstract: We investigate the effects on parameter estimation of including amplitude corrections to post-Newtonian (PN) gravitational waveforms for the quasi-circular, adiabatic inspiral of binary compact objects. The amplitude-corrected waveforms are superpositions of harmonics of the orbital phase. Their performance is compared with that of the restricted PN waveforms, which only have the dominant harmonic at twice the orbital phase, with no amplitude corrections. For concreteness we consider parameter estimation in the covariance matrix formalism for Advanced LIGO as well as a possible third-generation detector tentatively called EGO. We use the stationary phase approximation to the Fourier transform of waveforms at 2.5PN order in amplitude and in phase, with inclusion of spin-related contributions to the phasing up to 2PN order. It is found that the use of such high-order amplitude-corrected waveforms leads to a dramatic improvement in the quality of parameter estimation. With restricted waveforms the errors are steep functions of the total mass of the binary, and accurate parameter extraction is only possible for relatively light stellar mass binaries. By contrast, at distances of $\sim 100$ Mpc the amplitude-corrected waveforms allow for high-accuracy parameter extraction for total masses up to several hundred solar masses. Other qualitative advantages include the measurability of individual component masses (which are poorly determined with restricted waveforms), and the possibility of finding objects whose spin exceeds the Kerr bound.

abs pdf

Oct 26, 2006

0610126 (/preprints/gr-qc)
2006-10-26, 19:35 [edit]

[gr-qc/0610122] Inspiral, merger and ring-down of equal-mass black-hole binaries

Authors: Alessandra Buonanno, Gregory B. Cook, Frans Pretorius

Date: Wed, 25 Oct 2006

Abstract: We investigate the dynamics and gravitational-wave (GW) emission in the binary merger of equal-mass black holes as obtained from numerical relativity simulations. Results from the evolution of three sets of initial data are explored in detail, corresponding to different initial separations of the black holes. We find that to a good approximation the inspiral phase of the evolution is quasi-circular, followed by a "blurred, quasi-circular plunge", then merger and ring down. We present first-order comparisons between analytical models of the various stages of the merger and the numerical results. We provide comparisons between the numerical results and analytical predictions based on the adiabatic Newtonain, post-Newtonian (PN), and non-adiabatic resummed-PN models. From the ring-down portion of the GW we extract the fundamental quasi-normal mode and several of the overtones. Finally, we estimate the optimal signal-to-noise ratio for typical binaries detectable by GW experiments.

abs pdf

Oct 25, 2006

0610122 (/preprints/gr-qc)
2006-10-25, 20:38 [edit]

[gr-qc/0610117] Isolation of gravitational waves from displacement noise and utility of a time-delay device

Authors: Kentaro Somiya, Keisuke Goda, Yanbei Chen, Eugeniy E. Mikhailov

Date: Wed, 25 Oct 2006

Abstract: Interferometers with kilometer-scale arms have been built for gravitational-wave detections on the ground; ones with much longer arms are being planned for space-based detection. One fundamental motivation for long baseline interferometry is from displacement noise. In general, the longer the arm length L, the larger the motion the gravitational-wave induces on the test masses, until L becomes comparable to the gravitational wavelength. Recently, schemes have been invented, in which displacement noises can be evaded by employing differences between the influence of test-mass motions and that of gravitational waves on light propagation. However, in these schemes, such differences only becomes significant when L approaches the gravitational wavelength, and shot-noise limited sensitivity becomes worse than that of conventional configurations by a factor of at least (f L/c)ˆ(-2), for f<c/L. Such a factor, although can be overcome theoretically by employing high optical powers, makes these schemes quite impractical. In this paper, we explore the use of time delay in displacement-noise-free interferometers, which can improve their shot-noise-limited sensitivity at low frequencies, to a factor of (f L/c)ˆ(-1) of the shot-noise-limited sensitivity of conventional configurations.

abs pdf

Oct 25, 2006

0610117 (/preprints/gr-qc)
2006-10-25, 20:38 [edit]

[astro-ph/0610657] Black-Hole Phenomenology

Authors: Neven Bilic

Date: Mon, 23 Oct 2006

Abstract: This set of lectures is an introduction to black-hole astrophysics. The emphasis is made on the phenomenology of X-ray binaries and of supermassive compact objects at galactic centers.

abs pdf

Oct 25, 2006

0610657 (/preprints/astro-ph)
2006-10-25, 10:20 [edit]

[astro-ph/0610680] Gravitational-wave background from compact objects embedded in AGN accretion disks

Authors: Guenter Sigl (APC and IAP, Paris), Jeremy Schnittman, Alessandra Buonanno (Univ. Maryland)

Date: Mon, 23 Oct 2006

Abstract: We consider a model in which massive stars form in a self-gravitating accretion disk around an active galactic nucleus (AGN). These stars may evolve and collapse to form compact objects on a time scale shorter than the accretion time, thus producing an important family of sources for LISA. Assuming the compact object formation/inspiral rate is proportional to the steady-state gas accretion rate, we use the intrinsic hard X-ray AGN luminosity function to estimate expected event rates and signal strengths. We find that these sources will produce a continuous low-frequency (<~ mHz) background detectable by LISA if more than 1% of the accreted matter is in the form of compact objects. For compact objects with masses >~ 10 solar masses the last stages of the inspiral events should be resolvable above a few mHz, with rates as high as a few hundred per year.

abs pdf

Oct 25, 2006

0610680 (/preprints/astro-ph)
2006-10-25, 10:19 [edit]

[gr-qc/0610099] Determination of the internal structure of neutron stars from gravitational wave spectra

Authors: L.K. Tsui, P.T. Leung, J. Wu

Date: Fri, 20 Oct 2006

Abstract: In this paper the internal structure of a neutron star is shown to be inferrable from its gravitational-wave spectrum. Iteratively applying the inverse scheme of the scaled coordinate logarithmic perturbation method for neutron stars proposed by Tsui and Leung [Astrophys. J. {\bf 631}, 495 (2005)], we are able to determine the mass, the radius and the mass distribution of a star from its quasi-normal mode frequencies of stellar pulsation. In addition, accurate equation of state of nuclear matter can be obtained from such inversion scheme. Explicit formulas for the case of axial $w$-mode oscillation are derived here and numerical results for neutron stars characterized by different equations of state are shown.

abs pdf

Oct 23, 2006

0610099 (/preprints/gr-qc)
2006-10-23, 08:56 [edit]

[astro-ph/0610478] Intermediate-mass black holes in colliding clusters: Implications for lower-frequency gravitational-wave astronomy

Authors: Pau Amaro-Seoane, Marc Freitag

Date: Mon, 16 Oct 2006

Abstract: Observations suggest that star clusters often form in binaries or larger bound groups. Therefore, mergers between two clusters are likely to occur. If these clusters both harbor an intermediate-mass black hole (IMBH; 10ˆ{2-4} Msun) in their center, they can become a strong source of gravitational waves when the black holes merge with each other. In order to understand the dynamical processes that operate in such a scenario, one has to study the evolution of the merger of two such young massive star clusters, and more specifically, their respective IMBHs. We employ the direct-summation Nbody4 numerical tool on special-purpose GRAPE6 hardware to simulate a merger of two stellar clusters each containing 63,000 particles and a central IMBH. This allows us to study accurately the orbital evolution of the colliding clusters and the embedded massive black holes. Within ~7 Myr the clusters have merged and the IMBHs constitute a hard binary. The final coalescence happens in ~10ˆ8 yrs. The implication of our analysis is that intermediate-mass black holes merging as the result of coalescence of young dense clusters could provide a source for the Laser Interferometer Space Antenna (LISA) space-based gravitational wave detector mission. We find that interactions with stars increase the eccentricity of the IMBH binary to about 0.8. Although the binary later circularizes by emission of gravitational waves, the residual eccentricity can be detectable through its influence on the phase of the waves if the last few years of inspiral are observed.

abs pdf

Oct 18, 2006

0610478 (/preprints/astro-ph)
2006-10-18, 18:05 [edit]

[quant-ph/0610131] Quantum Physics and Human Language

Authors: James B. Hartle (University of California, Santa Barbara)

Date: Mon, 16 Oct 2006

Abstract: Human languages employ constructions that tacitly assume specific properties of the limited range of phenomena they evolved to describe. These assumed properties are true features of that limited context, but may not be general or precise properties of all the physical situations allowed by fundamental physics. In brief, human languages contain ‘excess baggage’ that must be qualified, discarded, or otherwise reformed to give a clear account in the context of fundamental physics of even the everyday phenomena that the languages evolved to describe. The surest route to clarity is to express the constructions of human languages in the language of fundamental physical theory, not the other way around. These ideas are illustrated by an analysis of the verb ‘to happen’ and the word ‘reality’ in special relativity and the modern quantum mechanics of closed systems.

abs pdf

Oct 18, 2006

0610131 (/preprints/quant-ph)
2006-10-18, 18:05 [edit]

[gr-qc/0610046] Detecting extreme mass ratio inspiral events in LISA data using the Hierarchical Algorithm for Clusters and Ridges (HACR)

Authors: Jonathan R Gair, Gareth Jones

Date: Tue, 10 Oct 2006

Abstract: One of the most exciting prospects for the Laser Interferometer Space Antenna (LISA) is the detection of gravitational waves from the inspirals of stellar-mass compact objects into supermassive black holes. Detection of these sources is an extremely challenging computational problem due to the large parameter space and low amplitude of the signals. However, recent work has suggested that the nearest extreme mass ratio inspiral (EMRI) events will be sufficiently loud that they might be detected using computationally cheap, template-free techniques, such as a time-frequency analysis. In this paper, we examine a particular time-frequency algorithm, the Hierarchical Algorithm for Clusters and Ridges (HACR). This algorithm searches for clusters in a power map and uses the properties of those clusters to identify signals in the data. We find that HACR applied to the raw spectrogram performs poorly, but when the data is binned during the construction of the spectrogram, the algorithm can detect typical EMRI events at distances of up to ~2.5Gpc. This is a little further than the simple Excess Power method that has been considered previously. We discuss the HACR algorithm, including tuning for single and multiple sources, and illustrate its performance for detection of typical EMRI events, and other likely LISA sources, such as white dwarf binaries and supermassive black hole mergers. We also discuss how HACR cluster properties can be used for parameter extraction.

abs pdf

Oct 10, 2006

0610046 (/preprints/gr-qc)
2006-10-10, 17:41 [edit]

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