## [0811.3012] Black hole quasinormal mode spectroscopy with LISA

Authors: Manish M. Jadhav, Lior M. Burko

Date: 19 Nov 2008

Abstract: The signal-to-noise ratio (SNR) for black hole quasinormal mode sources of low-frequency gravitational waves is estimated using a Monte Carlo approach that replaces the all-sky average approximation. We consider an eleven dimensional parameter space that includes both source and detector parameters. We find that in the black-hole mass range $M\sim 4$-$10\times 10ˆ6M_{\odot}$ the SNR is significantly higher than the SNR for the all-sky average case, as a result of the variation of the spin parameter of the sources. This increased SNR may translate to a higher event rate for the Laser Interferometer Space Antenna (LISA). We also study the directional dependence of the SNR, and show at which directions in the sky LISA will have greater response.

#### Nov 25, 2008

0811.3012 (/preprints)
2008-11-25, 21:09 

## [0811.3582] Detecting a Stochastic Gravitational-Wave Background: The Overlap Reduction Function

Authors: Lee Samuel Finn, Shane L. Larson, Joseph D. Romano

Date: 21 Nov 2008

Abstract: Detection of a gravitational-wave stochastic background via ground or space-based gravitational-wave detectors requires the cross-correlation of the response of two or more independent detectors. The cross-correlation involves a frequency-dependent factor -- the so-called overlap reduction function or Hellings-Downs curve -- that depends on the relative geometry of each detector pair: i.e., the detector separations and the relative orientation of their antenna patterns (beams). An incorrect formulation of this geometrical factor has appeared in several places in the literature, leading to incorrect conclusions regarding the sensitivity of proposed detectors to a stochastic gravitational-wave background. To rectify these errors and as a reference for future work we provide here a complete, first-principles derivation of the overlap reduction function and assess the nature of the errors associated with the use of the incorrect expression that has appeared in the literature. We describe the behavior of the overlap reduction function in different limiting regimes, and show how the difference between the correct and incorrect expressions can be understood physically.

#### Nov 25, 2008

0811.3582 (/preprints)
2008-11-25, 21:09 

## [0811.3924] The effect of general relativity on hyperbolic orbits and its application to the flyby anomaly

Authors: Lorenzo Iorio

Date: 24 Nov 2008

Abstract: We investigate qualitatively and quantitatively the impact of the general relativistic gravito-electromagnetic forces on hyperbolic orbits around a massive spinning body. The gravito-magnetic field, which is the cause of the well known Lense-Thirring precessions of elliptic orbits, is induced by the spin $\bds S$ of the central body. It deflects and displaces the trajectories differently according to the mutual orientation of S and the orbital angular momentum L of the test particle. The gravito-electric force, which induces the Einstein precession of the perihelion of the orbit of Mercury, always deflects inward the trajectories irrespectively to the L-S orientation. We numerically compute their effect on the range r, radial and transverse components v_r and v_\tau of the velocity and speed v of the NEAR spacecraft at its closest approach with the Earth in January 1998 when it experienced an anomalous increase of its asymptotic outgoing velocity v_\infty o of 13.46 +/- 0.01 mm secˆ-1. The range-rate and the speed are affected by general relativistic gravito-electromagnetism at 10ˆ-2-10ˆ-5 mm secˆ-1 level. The changes in the range are of the order of 10ˆ-2-10ˆ1 mm.

#### Nov 25, 2008

0811.3924 (/preprints)
2008-11-25, 21:08 

## [0811.3952] Black-hole binary simulations: the mass ratio 10:1

Authors: Jose A. Gonzalez, Ulrich Sperhake, Bernd Bruegmann

Date: 24 Nov 2008

Abstract: We present the first numerical simulations of an initially non-spinning black-hole binary with mass ratio as large as 10:1 in full general relativity. The binary completes approximately 3 orbits prior to merger and radiates about 0.415% of the total energy and 12.48% of the initial angular momentum in the form of gravitational waves. The single black hole resulting from the merger acquires a kick of about 66.7 km/s relative to the original center of mass frame. The resulting gravitational waveforms are used to validate existing formulas for the recoil, final spin and radiated energy over a wider range of the symmetric mass ratio parameter eta=M1*M2/(M1+M2)ˆ2 than previously possible. The contributions of l > 2 multipoles are found to visibly influence the gravitational wave signal obtained at fixed inclination angles.

#### Nov 25, 2008

0811.3952 (/preprints)
2008-11-25, 21:08 

## [0811.3451] Gravitational-wave memory revisited: memory from the merger and recoil of binary black holes

Authors: Marc Favata

Date: 21 Nov 2008

Abstract: Gravitational-wave memory refers to the permanent displacement of the test masses in an idealized (freely-falling) gravitational-wave interferometer. Inspiraling binaries produce a particularly interesting form of memory--the Christodoulou memory. Although it originates from nonlinear interactions at 2.5 post-Newtonian order, the Christodoulou memory affects the gravitational-wave amplitude at leading (Newtonian) order. Previous calculations have computed this non-oscillatory amplitude correction during the inspiral phase of binary coalescence. Using an "effective-one-body" description calibrated with the results of numerical relativity simulations, the evolution of the memory during the inspiral, merger, and ringdown phases, and the memory's final saturation value, are calculated. Using this model for the memory, the prospects for its detection are examined, particularly for supermassive black hole binary coalescences that LISA will detect with high signal-to-noise ratios. Coalescing binary black holes also experience center-of-mass recoil due to the anisotropic emission of gravitational radiation. These recoils can manifest themselves in the gravitational-wave signal in the form of a "linear" memory and a Doppler shift of the quasi-normal-mode frequencies. The prospects for observing these effects are also discussed.

#### Nov 25, 2008

0811.3451 (/preprints)
2008-11-25, 21:08 

## [0811.3772] What if Time Really Exists?

Authors: Sean M. Carroll

Date: 23 Nov 2008

Abstract: Despite the obvious utility of the concept, it has often been argued that time does not exist. I take the opposite perspective: let's imagine that time does exist, and the universe is described by a quantum state obeying ordinary time-dependent quantum mechanics. Reconciling this simple picture with the known facts about our universe turns out to be a non-trivial task, but by taking it seriously we can infer deep facts about the fundamental nature of reality. The arrow of time finds a plausible explanation in a "Heraclitean universe," described by a quantum state eternally evolving in an infinite-dimensional Hilbert space.

#### Nov 25, 2008

0811.3772 (/preprints)
2008-11-25, 21:07 

## [0811.3798] Dynamics of Black Hole Pairs II: Spherical Orbits and the Homoclinic Limit of Zoom-Whirliness

Authors: Rebecca Grossman, Janna Levin

Date: 24 Nov 2008

Abstract: Spinning black hole pairs exhibit a range of complicated dynamical behaviors. An interest in eccentric and zoom-whirl orbits has ironically inspired the focus of this paper: the constant radius orbits. When black hole spins are misaligned, the constant radius orbits are not circles but rather lie on the surface of a sphere and have acquired the name "spherical orbits". The spherical orbits are significant as they energetically frame the distribution of all orbits. In addition, each unstable spherical orbit is asymptotically approached by an orbit that whirls an infinite number of times, known as a homoclinic orbit. A homoclinic trajectory is an infinite whirl limit of the zoom-whirl spectrum and has a further significance as the separatrix between inspiral and plunge for eccentric orbits. We work in the context of two spinning black holes of comparable mass as described in the 3PN Hamiltonian with spin-orbit coupling included. As such, the results could provide a testing ground of the accuracy of the PN expansion. Further, the spherical orbits could provide useful initial data for numerical relativity. Finally, we comment that the spinning black hole pairs should give way to chaos around the homoclinic orbit when spin-spin coupling is incorporated.

#### Nov 25, 2008

0811.3798 (/preprints)
2008-11-25, 21:07 

## [0811.3814] Homoclinic Orbits around Spinning Black Holes I: Exact Solution for the Kerr Separatrix

Authors: Janna Levin, Gabe Perez-Giz

Date: 24 Nov 2008

Abstract: Under the dissipative effects of gravitational radiation, black hole binaries will transition from an inspiral to a plunge. The separatrix between bound and plunging orbits features prominently in the transition. For equatorial Kerr orbits, we show that the separatrix is a homoclinic orbit in one-to-one correspondence with an energetically-bound, unstable circular orbit. After providing a definition of homoclinic orbits, we exploit their correspondence with circular orbits and derive exact solutions for them. This paper focuses on homoclinic behavior in physical space, while in a companion paper we paint the complementary phase space portrait. The exact results for the Kerr separatrix could be useful for analytic or numerical studies of the transition from inspiral to plunge.

#### Nov 25, 2008

0811.3814 (/preprints)
2008-11-25, 21:07 

## [0811.3815] Homoclinic Orbits around Spinning Black Holes II: The Phase Space Portrait

Authors: Gabe Perez-Giz, Janna Levin

Date: 24 Nov 2008

Abstract: In paper I in this series, we found exact expressions for the equatorial homoclinic orbits: the separatrix between bound and plunging, whirling and not whirling. As a companion to that physical space study, in this paper we paint a phase space portrait of the homoclinic orbits that includes exact expressions for the actions and fundamental frequencies. Additionally, we develop a reduced Hamiltonian description of Kerr motion that allows us to track groups of trajectories with a single global clock. This facilitates a variational analysis, whose stability exponents and eigenvectors could potentially be useful for future studies of families of black hole orbits and their associated gravitational waveforms.

#### Nov 25, 2008

0811.3815 (/preprints)
2008-11-25, 21:07 

## [0811.3006] Algebraic Classification of Numerical Spacetimes and Black-Hole-Binary Remnants

Authors: Manuela Campanelli, Carlos O. Lousto, Yosef Zlochower

Date: 18 Nov 2008

Abstract: In this paper we develop a technique for determining the algebraic classification of a numerical spacetime, possibly resulting from a generic black-hole-binary merger, using the Newman-Penrose Weyl scalars. We demonstrate these techniques for a test case involving a close binary with arbitrarily oriented spins and unequal masses. We find that, post merger, the spacetime quickly approaches Petrov type II, and only approaches type D on much longer timescales. These techniques allow us to begin to explore the validity of the "no-hair theorem" for generic merging-black-hole spacetimes.

#### Nov 20, 2008

0811.3006 (/preprints)
2008-11-20, 09:39 

## [0811.2069] Improved resummation of post-Newtonian multipolar waveforms from circularized compact binaries

Authors: Thibault Damour, Bala R. Iyer, Alessandro Nagar

Date: 13 Nov 2008

Abstract: We improve and generalize a resummation method of post-Newtonian multipolar waveforms from circular compact binaries introduced in Refs. \cite{Damour:2007xr,Damour:2007yf}. One of the characteristic features of this resummation method is to replace the usual {\it additive} decomposition of the standard post-Newtonian approach by a {\it multiplicative} decomposition of the complex multipolar waveform $h_{\lm}$ into several (physically motivated) factors: (i) the ‘Newtonian’ waveform, (ii) a relativistic correction coming from an ‘effective source’, (iii) leading-order tail effects linked to propagation on a Schwarzschild background, (iv) a residual tail dephasing, and (v) residual relativistic amplitude corrections $f_{\lm}$. We explore here a new route for resumming $f_{\lm}$ based on replacing it by its $\ell$-th root: $\rho_{\lm}=f_{\lm}ˆ{1/\ell}$. In the extreme-mass-ratio case, this resummation procedure results in a much better agreement between analytical and numerical waveforms than when using standard post-Newtonian approximants. We then show that our best approximants behave in a robust and continuous manner as we ‘deform’ them by increasing the symmetric mass ratio $\nu\equiv m_1 m_2/(m_1+m_2)ˆ2$ from 0 (extreme-mass-ratio case) to ¼ (equal-mass case). The present paper also completes our knowledge of the first post-Newtonian corrections to multipole moments by computing ready-to-use explicit expressions for the first post-Newtonian contributions to the odd-parity (current) multipoles.

#### Nov 13, 2008

0811.2069 (/preprints)
2008-11-13, 21:44 

## [0811.1998] Gravity theory that passes the classical tests but does not have black holes

Authors: Alexander Torres-Gomez, Kirill Krasnov

Date: 12 Nov 2008

Abstract: We revisit a propagating torsion gravity theory obtained by introducing a field coupled to the topological term in the first-order Einstein-Cartan action. The resulting theory has second order field equations, no adjustable coupling constants, and one more propagating degree of freedom as compared to general relativity. Thus, one might suspect that it should be easily ruled out by e.g. the solar system tests. To see whether this is the case, we obtain the spherically-symmetric solution of the theory, and show that it is characterized by the usual mass and an additional parameter. To our great surprise we find that the leading order corrections to the usual Newtonian behaviour are exactly as in general relativity, and, in particular, are independent of the new parameter. Thus, the theory passes the classical gravity tests. The analysis of the global structure of the solution leads to yet another surprising feature of the theory: the spherically-symmetric solution is never a black hole. One either has a naked curvature singularity or a wormhole solution connecting two asymptotic regions.

#### Nov 13, 2008

0811.1998 (/preprints)
2008-11-13, 21:44 

## [0811.1011] Massive Black Hole Binary Inspirals: Results from the LISA Parameter Estimation Taskforce

Authors: K. G. Arun, Stas Babak, Emanuele Berti, Neil Cornish, Curt Cutler, Jonathan Gair, Scott A. Hughes, Bala R. Iyer, Ryan N. Lang, Ilya Mandel, Edward K. Porter, Bangalore S. Sathyaprakash, Siddhartha Sinha, Alicia M. Sintes, Miquel Trias, Chris Van Den Broeck, Marta Volonteri

Date: 6 Nov 2008

Abstract: The LISA Parameter Estimation (LISAPE) Taskforce was formed in September 2007 to provide the LISA Project with vetted codes, source distribution models, and results related to parameter estimation. The Taskforce's goal is to be able to quickly calculate the impact of any mission design changes on LISA's science capabilities, based on reasonable estimates of the distribution of astrophysical sources in the universe. This paper describes our Taskforce's work on massive black-hole binaries (MBHBs). Given present uncertainties in the formation history of MBHBs, we adopt four different population models, based on (i) whether the initial black-hole seeds are small or large, and (ii) whether accretion is efficient or inefficient at spinning up the holes. We compare four largely independent codes for calculating LISA's parameter-estimation capabilities. All codes are based on the Fisher-matrix approximation, but in the past they used somewhat different signal models, source parametrizations and noise curves. We show that once these differences are removed, the four codes give results in extremely close agreement with each other. Using a code that includes both spin precession and higher harmonics in the gravitational-wave signal, we carry out Monte Carlo simulations and determine the number of events that can be detected and accurately localized in our four population models.

#### Nov 08, 2008

0811.1011 (/preprints)
2008-11-08, 07:19 

## [gr-qc/0409054] What is a particle?

Authors: Daniele Colosi, Carlo Rovelli

Date: 14 Sep 2004

Abstract: Theoretical developments related to the gravitational interaction have questioned the notion of particle in quantum field theory (QFT). For instance, uniquely-defined particle states do not exist in general, in QFT on a curved spacetime. More in general, particle states are difficult to define in a background-independent quantum theory of gravity. These difficulties have lead some to suggest that in general QFT should not be interpreted in terms of particle states, but rather in terms of eigenstates of local operators. Still, it is not obvious how to reconcile this view with the empirically-observed ubiquitous particle-like behavior of quantum fields, apparent for instance in experimental high-energy physics, or "particle"-physics. Here we offer an element of clarification by observing that already in flat space there exist --strictly speaking-- two distinct notions of particles: globally defined $n$-particle Fock-states and *local particle states*. The last describe the physical objects detected by finite-size particle detectors and are eigenstates of local field operators. In the limit in which the particle detectors are appropriately large, global and local particle states converge in a weak topology (but not in norm). This observation has little relevance for flat-space theories --it amounts to a reminder that there are boundary effects in realistic detectors--; but is relevant for gravity. It reconciles the two points of view mentioned above. More importantly, it provides a definition of local particle state that remains well-defined even when the conventional global particle states are not defined. This definition plays an important role in quantum gravity.

#### Nov 08, 2008

0409054 (/preprints/gr-qc)
2008-11-08, 07:18 

## [0810.3235] Inspiralling Supermassive Black Holes: A New Signpost for Galaxy Mergers

Authors: Julia M. Comerford, Brian F. Gerke, Jeffrey A. Newman, Marc Davis, Renbin Yan, Michael C. Cooper, S.M. Faber, David C. Koo, Alison L. Coil, D.J. Rosario

Date: 19 Oct 2008

Abstract: Because structure in the Universe is built up through galaxy mergers and nearly all galaxies host a central supermassive black hole (SMBH), some galaxies should possess two SMBHs near their centers as the result of a recent merger. These SMBHs spiral to the center of the resultant merger-remnant galaxy, and one or both of the SMBHs may power active galactic nuclei (AGN). Using the DEEP2 Galaxy Redshift Survey we have examined 1881 early-type galaxies, of which 107 exhibit [O III] and Hbeta emission lines indicative of AGN activity. Of these, 37 AGN have [O III] emission-line redshifts significantly different from the redshifts of the host galaxies' stars, corresponding to velocity offsets of ~50 km/s to ~300 km/s. Two of these AGN exhibit double-peaked [O III] emission lines, while the remaining 35 AGN each exhibit a single set of velocity-offset [O III] emission lines. These AGN velocity offsets cannot be readily explained by outflows, but rather are most likely the result of recent galaxy mergers. Based on this interpretation we find that roughly half of early-type galaxies hosting AGN are also merger remnants, which implies that mergers may trigger AGN activity in early-type galaxies. Our result sets a hard lower limit of 2.0% on the fraction of early-type galaxies at redshifts 0.34 < z < 0.82 that have recently undergone mergers. We also find a merger rate of ~3 mergers/Gyr, which includes both minor and major mergers, for early-type galaxies at redshifts 0.34 < z < 0.82.

#### Nov 07, 2008

0810.3235 (/preprints)
2008-11-07, 08:41 

## [0810.5125] Advanced localization of massive black hole coalescences with LISA

Authors: Ryan N. Lang, Scott A. Hughes

Date: 28 Oct 2008

Abstract: The coalescence of massive black holes is one of the primary sources of gravitational waves (GWs) for LISA. Measurements of the GWs can localize the source on the sky to an ellipse with a major axis of a few tens of arcminutes to a few degrees, depending on source redshift, and a minor axis which is 2--4 times smaller. The distance (and thus an approximate redshift) can be determined to better than a percent for the closest sources we consider, although weak lensing degrades this performance. It will be of great interest to search this three-dimensional "pixel" for an electromagnetic counterpart to the GW event. The presence of a counterpart allows unique studies which combine electromagnetic and GW information, especially if the counterpart is found prior to final merger of the holes. To understand the feasibility of early counterpart detection, we calculate the evolution of the GW pixel with time. We find that the greatest improvement in pixel size occurs in the final day before merger, when spin precession effects are maximal. The source can be localized to within 10 square degrees as early as a month before merger at $z = 1$; for higher redshifts, this accuracy is only possible in the last few days.

#### Nov 04, 2008

0810.5125 (/preprints)
2008-11-04, 09:23 

## [0810.5727] LISA as a dark energy probe

Authors: K G Arun, Chandrakant Mishra, Chris Van Den Broeck, B R Iyer, B S Sathyaprakash, Siddhartha Sinha

Date: 31 Oct 2008

Abstract: Recently it was shown that the inclusion of higher signal harmonics in the inspiral signals of binary supermassive black holes (SMBH) leads to dramatic improvements in parameter estimation with the Laser Interferometer Space Antenna (LISA). In particular, the angular resolution becomes good enough to identify the host galaxy or galaxy cluster, in which case the redshift can be determined by electromagnetic means. The gravitational wave signal also provides the luminosity distance with high accuracy, and the relationship between this and the redshift depends sensitively on the cosmological parameters, such as the equation-of-state parameter $w=p_{\rm DE}/\rho_{\rm DE}$ of dark energy. With a single binary SMBH event at $z < 1$ having appropriate masses and orientation, one would be able to constrain $w$ to within a few percent. We show that, if the measured sky location is folded into the error analysis, the uncertainty on $w$ goes down by an additional factor of 2-3, leaving weak lensing as the only limiting factor in using LISA as a dark energy probe.

#### Nov 04, 2008

0810.5727 (/preprints)
2008-11-04, 08:54 

## [0810.5541] Double Binary Pulsar Test of Dynamical Chern-Simons Modified Gravity

Authors: Nicolas Yunes, David N. Spergel

Date: 30 Oct 2008

Abstract: Gravitational parity violation is inherent in string theory, one effective model of which is Chern-Simons modified gravity. This effective theory introduces a parity-violating modification to the Einstein equations, whose magnitude depends on derivatives of the Chern-Simons coupling. In the dynamical formulation, this coupling is an evolving field that is sourced by spacetime curvature. We here calculate the Chern-Simons modification to the orbital evolution of a binary system of spinning compact objects in the weak-field. The ratio of the Chern-Simons correction to perigee precession to the general relativistic prediction is found to scale quadratically with the semi-major axis and inversely with the square of the object's radius. Binary pulsar systems are ideal to test this theory, since perigee precession can be measured with sub-degree accuracies and the semi-major axis is millions of times larger than the stellar radius. We find that observations of perigee precession from the double binary pulsar PSR J 0737-3039 A/B dramatically constrain the Chern-Simons coupling, M_(CS) := |\dot{\theta}|ˆ(-1) > 50 meV, approximately a hundred billion times better than Solar System tests.

#### Nov 04, 2008

0810.5541 (/preprints)
2008-11-04, 08:54 

## [0810.5707] Supernova waveform catalogue decompositon: a Principal Component Analysis approach

Authors: Ik Siong Heng

Date: 31 Oct 2008

Abstract: This paper introduces the use of Principal Component Analysis as a method to decompose the waveform catalogues to produce a set of orthonormal basis vectors. We apply this method to a set of supernova waveforms and compare the basis vectors obtained with those obtained through Gram-Schmidt decomposition. We observe that, for the chosen set of waveforms, the performance of the two methods are comparable for minimal match requirements up to 0.9, with 14 Gram-Schmidt basis vectors and 12 principal components required for a minimal match of 0.9. This implies that there are many common features in the chosen waveforms. Additionally, we observe the chosen waveforms have very similar features and a minimal match of 0.7 can be obtained by decomposing only one third of the entire set of waveforms in the chosen catalogue. We discuss the implications of this observation and the advantages of eigen-decomposing waveform catalogues with Principal Component Analysis.

#### Nov 04, 2008

0810.5707 (/preprints)
2008-11-04, 08:53 

## [0811.0188] Probing black holes at low redshift using LISA EMRI observations

Authors: Jonathan R Gair

Date: 2 Nov 2008

Abstract: One of the most exciting potential sources of gravitational waves for the Laser Interferometer Space Antenna (LISA) are the inspirals of approximately stellar mass compact objects into massive black holes in the centres of galaxies - extreme mass ratio inspirals (EMRIs). LISA should observe between a few tens and a few hundred EMRIs over the mission lifetime, mostly at low redshifts (z < 1). Each observation will provide a measurement of the parameters of the host system to unprecendented precision. LISA EMRI observations will thus offer a new and unique way to probe black holes at low redshift. In this article we provide a description of the population of EMRI events that LISA is likely to observe, and how the numbers of events vary with changes in the underlying assumptions about the black hole population. We also provide fitting functions that characterise LISA's ability to detect EMRIs and which will allow LISA event rates to be computed for arbitrary population models. We finish with a discussion of an ongoing programme that will use these results to assess what constraints LISA observations could place on galaxy evolution models.

#### Nov 04, 2008

0811.0188 (/preprints)
2008-11-04, 08:53 

## [0811.0294] Simulations of Extreme-Mass-Ratio Inspirals Using Pseudospectral Methods

Authors: Priscilla Canizares, Carlos F. Sopuerta (ICE, CSIC-IEEC)

Date: 3 Nov 2008

Abstract: Extreme-mass-ratio inspirals (EMRIs), stellar-mass compact objects (SCOs) inspiralling into a massive black hole, are one of the main sources of gravitational waves expected for the Laser Interferometer Space Antenna (LISA). To extract the EMRI signals from the expected LISA data stream, which will also contain the instrumental noise as well as other signals, we need very accurate theoretical templates of the gravitational waves that they produce. In order to construct those templates we need to account for the gravitational backreaction, that is, how the gravitational field of the SCO affects its own trajectory. In general relativity, the backreaction can be described in terms of a local self-force, and the foundations to compute it have been laid recently. Due to its complexity, some parts of the calculation of the self-force have to be performed numerically. Here, we report on an ongoing effort towards the computation of the self-force based on time-domain multi-grid pseudospectral methods.

#### Nov 04, 2008

0811.0294 (/preprints)
2008-11-04, 08:53 

## [0811.0138] Can we Detect Intermediate Mass Ratio Inspirals?

Authors: Ilya Mandel, Jonathan R. Gair

Date: 2 Nov 2008

Abstract: Gravitational waves emitted during intermediate-mass-ratio inspirals (IMRIs) of intermediate-mass black holes (IMBHs) into supermassive black holes could represent a very interesting source for LISA. Similarly, IMRIs of stellar-mass compact objects into IMBHs could be detectable by Advanced LIGO. At present, however, it is not clear what waveforms could be used for IMRI detection, since the post-Newtonian approximation breaks down as an IMRI approaches the innermost stable circular orbit, and perturbative solutions are only known to the lowest order in the mass ratio. We discuss the expected mismatches between approximate and true waveforms, and the choice of the best available waveform as a function of the mass ratio and the total mass of the system. We also comment on the significance of the spin of the smaller body and the need for its inclusion in the waveforms.

#### Nov 04, 2008

0811.0138 (/preprints)
2008-11-04, 08:52 

## [0811.0181] Constraining effective quantum gravity with LISA

Authors: Nicolas Yunes, Lee Samuel Finn

Date: 2 Nov 2008

Abstract: All modern routes leading to a quantum theory of gravity -- i.e., perturbative quantum gravitational one-loop exact correction to the global chiral current in the standard model, string theory, and perhaps even loop quantum gravity -- require supplementing the Einstein-Hilbert action with a parity-violating Chern-Simons term. Such a term leads to amplitude-birefringent gravitational wave propagation: i.e., one (circular) polarization state amplified with propagation while the other is attenuated. The proposed Laser Interferometer Space Antenna (LISA) is capable of observing gravitational wave sources at cosmological distances, suggesting the possibility that LISA observations may place a strong bound on this manifestation of quantum gravity. Here we report on a calculation of the effect that spacetime amplitude birefringence has on the signal LISA is capable of observing from inspiraling supermassive black hole binaries at large redshift. We find that the birefringence manifests itself in the observations as an anomalous precession of the binary's orbital angular momentum as it evolves toward coalescence, whose magnitude depends on the integrated history of the Chern-Simons coupling over the worldline of radiation wavefront. We estimate that LISA could place bounds on Chern-Simons modified gravity that are several orders of magnitude stronger than the present Solar System constraints, thus providing a probe of the quantum structure of spacetime.

#### Nov 04, 2008

0811.0181 (/preprints)
2008-11-04, 08:52