## [1205.3926] Influence of internal structure on the motion of test bodies in extreme mass ratio situations

Authors: Jan Steinhoff, Dirk Puetzfeld

Date: 17 May 2012

Abstract: We investigate the motion of test bodies with internal structure in General Relativity. With the help of a multipolar approximation method for extended test bodies we derive the equations of motion up to the quadrupolar order. The motion of pole-dipole and quadrupole test bodies is studied in the context of the Kerr geometry. For an explicit quadrupole model, which includes spin and tidal interactions, the motion in the equatorial plane is characterized by an effective potential and by the binding energy. We compare our findings to recent results for the conservative part of the self-force of bodies in extreme mass ratio situations. Possible implications for gravitational wave physics are outlined.

#### May 24, 2012

1205.3926 (/preprints)
2012-05-24, 14:26 

## [1205.4530] On the comparison of results regarding the post-Newtonian approximate treatment of the dynamics of extended spinning compact binaries

Authors: Steven Hergt, Jan Steinhoff, Gerhard Schaefer

Date: 21 May 2012

Abstract: A brief review is given of all the Hamiltonians and effective potentials calculated hitherto covering the post-Newtonian (pN) dynamics of a two body system. A method is presented to compare (conservative) reduced Hamiltonians with nonreduced potentials directly at least up to the next-to-leading-pN order.

#### May 24, 2012

1205.4530 (/preprints)
2012-05-24, 14:25 

## [1205.4620] Single-detector searches for a stochastic background of gravitational radiation

Authors: Massimo Tinto, J. W. Armstrong

Date: 21 May 2012

Abstract: We propose a data processing technique that allows searches for a stochastic background of gravitational radiation with data from a single detector. Our technique exploits the difference between the coherence time of the gravitational wave (GW) signal and that of the instrumental noise affecting the measurements. By estimating the auto-correlation function of the data at an off-set time that is longer than the coherence time of the noise {\underbar {but}} shorter than the coherence time of the GW signal, we can effectively enhance the power signal-to-noise ratio (SNR) by the square-root of the integration time. The resulting SNR is comparable in magnitude to that achievable by cross-correlating the data from two co-located and co-aligned detectors whose noises are uncorrelated. Our method is general and it can be applied to data from ground- and space-based detectors, as well as from pulsar timing experiments.

#### May 24, 2012

1205.4620 (/preprints)
2012-05-24, 14:25 

## [1205.4440] The representation of physical motions by various types of quaternions

Authors: D. H. Delphenich

Date: 20 May 2012

Abstract: It is shown that the groups of Euclidian rotations, rigid motions, proper, orthochronous Lorentz transformations, and the complex rigid motions can be represented by the groups of unit-norm elements in the algebras of real, dual, complex, and complex dual quaternions, respectively. It is shown how someof the physically-useful tensors and spinors can be represented by the various kinds of quaternions. The basic notions of kinematical states are described in each case, except complex dual quaternions, where their possible role in describing the symmetries of the Maxwell equations is discussed.

#### May 24, 2012

1205.4440 (/preprints)
2012-05-24, 14:24 

## [1205.4713] The role of the supermassive black hole spin in the estimation of the EMRI event rate

Authors: Pau Amaro-Seoane, Carlos F. Sopuerta, Marc Dewi Freitag

Date: 21 May 2012

Abstract: One of the main channels of interactions in galactic nuclei between stars and the central massive black hole (MBH) is the gradual inspiral of compact remnants into the MBH due to the emission of gravitational radiation. Previous works about the estimation of how many events space observatories such as LISA will be able to observe during its operational time differ in orders of magnitude, due to the complexity of the problem. Nevertheless, a common result to all investigations is that a plunge is much more likely than a slow adiabatic inspiral, an EMRI. The event rates for plunges are orders of magnitude larger than slow inspirals. On the other hand, nature MBH's are most likely Kerr and the magnitude of the spin has been sized up to be high. We calculate the number of periapsis passages that a compact object set on to an extremely radial orbit goes through before being actually swallowed by the Kerr MBH and we then translate it into an event rate for a LISA-like observatory. We prove that a "plunging" compact object is conceptually indistinguishable from an adiabatic, slow inspiral. This has an important impact on the event rate, enhancing in some cases significantly, depending on the spin of the MBH and the inclination: If the orbit of the EMRI is prograde, the effective size of the MBH becomes smaller the larger the spin is, whilst if retrograde, it becomes bigger. However, this situation is not symmetric, resulting in an effective enhancement of the rates. The effect of vectorial resonant relaxation on the sense of the orbit does not affect the enhancement. The strong dependence on the spin magnitude and orbital orientation of the EMRI on the rates will allow us to study stellar dynamics in a regime which is invisible to photon-based astrophysics.

#### May 24, 2012

1205.4713 (/preprints)
2012-05-24, 14:23 

## [1205.5017] Structure and evolution of circumbinary disks around supermassive black hole (SMBH) binaries

Authors: Roman R. Rafikov (Princeton)

Date: 22 May 2012

Abstract: It is generally believed that gaseous disks around supermassive black hole (SMBH) binaries in centers of galaxies can facilitate binary merger and give rise to observational signatures both in electromagnetic and gravitational wave domains. We explore general properties of circumbinary disks by reformulating standard equations for the viscous disk evolution in terms of the viscous angular momentum flux F_J. In steady state F_J is a linear function of the specific angular momentum, which is a generalization of (but is not equivalent to) the standard constant \dot M disk solution. If the torque produced by the central binary is effective at stopping gas inflow and opening a gap (or cavity) in the disk, then the inner part of the circumbinary disk can be approximated as a constant F_J disk. We compute properties of such disks in different physical regimes relevant for SMBH binaries and use these results to understand the gas-assisted evolution of SMBH pairs starting at separations 10ˆ{-4}-10ˆ{-2} pc. We find the following. (1) Pile-up of matter at the inner edge of the disk leads to continuous growth of the torque acting on the binary and can considerably accelerate its orbital evolution compared to the gravitational wave-driven decay. (2) Torque on the binary is determined non-locally and does not in general reflect the disk properties in the vicinity of the binary. (3) Binary evolution depends on the past history of the disk evolution. (4) Eddington limit can be important in circumbinary disks even if they accrete at sub-Eddington rates at late stages of binary evolution. (5) Circumbinary disk self-consistently evolved under the action of the binary torque emits more power and has spectrum different from the spectrum of constant \dot M disk - it is steeper (\nu F_\nu\propto \nuˆ{12/7}) and extends to shorter wavelength, facilitating its detection.

#### May 24, 2012

1205.5017 (/preprints)
2012-05-24, 14:22 

## [1205.5175] Orbit optimization for ASTROD-GW and its time delay interferometry with two arms using CGC ephemeris

Authors: G. Wang, W.-T. Ni

Date: 23 May 2012

Abstract: ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical Devices] optimized for Gravitation Wave detection) is an optimization of ASTROD to focus on the goal of detection of gravitation waves. The detection sensitivity is shifted 52 times toward larger wavelength compared to that of LISA. The mission orbits of the 3 spacecraft forming a nearly equilateral triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4 and L5. The 3 spacecraft range interferometrically with one another with arm length about 260 million kilometers. In order to attain the requisite sensitivity for ASTROD-GW, laser frequency noise must be suppressed below the secondary noises such as the optical path noise, acceleration noise etc. For suppressing laser frequency noise, we need to use time delay interferometry (TDI) to match the two different optical paths (times of travel). Since planets and other solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the (TDI), we simulate the time delay numerically using CGC 2.7 ephemeris framework. To conform to the ASTROD-GW planning, we work out a set of 20-year optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and calculate the residual optical path differences in the first and second generation TDI for one-detector case. In our optimized mission orbits for 20 years, changes of arm length are less than 0.0003 AU; the relative Doppler velocities are less than 3m/s. All the second generation TDI for one-detector case satisfies the ASTROD-GW requirement.

#### May 24, 2012

1205.5175 (/preprints)
2012-05-24, 14:21 

## [1205.5240] Stellar dynamics and extreme-mass ratio inspirals

Authors: Pau Amaro-Seoane

Date: 23 May 2012

Abstract: Nowadays it is well-established that in the centre of the Milky Way a massive black hole (MBH) with a mass of about four million solar masses is lurking. While there is an emerging consensus about the origin and growth of supermassive black holes (with masses larger than a billion solar masses), MBHs with smaller masses such as the one in our galactic centre remain an understudied enigma. The key to understanding these holes, how some of them grow by orders of magnitude in mass is to understand the dynamics of the stars in the galactic neighborhood. Stars and the central MBH chiefly interact through the gradual inspiral of the stars into the MBH due to the emission of gravitational radiation. Also stars produce gases which will be subsequently accreted by the MBH by collisions and disruptions brought about by the strong central tidal field. Such processes can contribute significantly to the mass of the MBH and progress in understanding them requires theoretical work in preparation for future gravitational radiation millihertz missions and X-ray observatories. In particular, a unique probe of these regions is the gravitational radiation that is emitted by some compact stars very close to the black holes and which will could be surveyed by a millihertz gravitational wave interferometer scrutinizing the range of masses fundamental to the understanding of the origin and growth of supermassive black holes. By extracting the information carried by the gravitational radiation, we can determine the mass and spin of the central MBH with unprecedented precision and we can determine how the holes "eat" stars that happen to be near them.

#### May 24, 2012

1205.5240 (/preprints)
2012-05-24, 14:21 

## [1205.4747] Principles of High-Dimensional Data Visualization in Astronomy

Authors: Alyssa A. Goodman

Date: 21 May 2012

Abstract: Astronomical researchers often think of analysis and visualization as separate tasks. In the case of high-dimensional data sets, though, interactive exploratory data visualization can give far more insight than an approach where data processing and statistical analysis are followed, rather than accompanied, by visualization. This paper attempts to charts a course toward "linked view" systems, where multiple views of high-dimensional data sets update live as a researcher selects, highlights, or otherwise manipulates, one of several open views. For example, imagine a researcher looking at a 3D volume visualization of simulated or observed data, and simultaneously viewing statistical displays of the data set's properties (such as an x-y plot of temperature vs. velocity, or a histogram of vorticities). Then, imagine that when the researcher selects an interesting group of points in any one of these displays, that the same points become a highlighted subset in all other open displays. Selections can be graphical or algorithmic, and they can be combined, and saved. For tabular (ASCII) data, this kind of analysis has long been possible, even though it has been under-used in Astronomy. The bigger issue for Astronomy and several other "high-dimensional" fields is the need systems that allow full integration of images and data cubes within a linked-view environment. The paper concludes its history and analysis of the present situation with suggestions that look toward cooperatively-developed open-source modular software as a way to create an evolving, flexible, high-dimensional, linked-view visualization environment useful in astrophysical research.

#### May 24, 2012

1205.4747 (/preprints)
2012-05-24, 14:21 

## [1205.4020] Secular Dynamical Anti-Friction in Galactic Nuclei

Date: 17 May 2012

Abstract: We identify a gravitational-dynamical process in near-Keplerian potentials of galactic nuclei that occurs when an intermediate-mass black hole (IMBH) is migrating on an eccentric orbit through the stellar cluster towards the central supermassive black hole (SMBH). We find that, apart from conventional dynamical friction, the IMBH experiences an often much stronger systematic torque due to the secular (i.e., orbit-averaged) interactions with the cluster's stars. The force which results in this torque is applied, counterintuitively, in the same direction as the IMBH's precession and we refer to its action as "secular-dynamical anti-friction" (SDAF). We argue that SDAF, and not the gravitational ejection of stars, is responsible for the IMBH's eccentricity increase seen in the initial stages of previous N-body simulations. Our numerical experiments, supported by qualitative arguments, demonstrate that (1) when the IMBH's precession direction is artificially reversed, the torque changes sign as well, which decreases the orbital eccentricity, (2) the rate of eccentricity growth is sensitive to the IMBH migration rate, with zero systematic eccentricity growth for an IMBH whose orbit is artificially prevented from inward migration, and (3) SDAF is the strongest when the central star cluster is rapidly rotating. This leads to eccentricity growth/decrease for the clusters rotating in the opposite/same direction relative to the IMBH's orbital motion.

#### May 21, 2012

1205.4020 (/preprints)
2012-05-21, 10:13 

## [1204.4218] Optimal strategies for continuous gravitational wave detection in pulsar timing arrays

Authors: Justin Ellis, Xavier Siemens, Jolien Creighton

Date: 18 Apr 2012

Abstract: Supermassive black hole binaries (SMBHBs) are expected to emit continuous gravitational waves in the pulsar timing array (PTA) frequency band ($10ˆ{-9}$--$10ˆ{-7}$ Hz). The development of data analysis techniques aimed at efficient detection and characterization of these signals is critical to the gravitational wave detection effort. In this paper we leverage methods developed for LIGO continuous wave gravitational searches, and explore the use of the $\mathcal{F}$-statistic for such searches in pulsar timing data. Babak & Sesana 2012 have already used this approach in the context of PTAs to show that one can resolve multiple SMBHB sources in the sky. Our work improves on several aspects of prior continuous wave search methods developed for PTA data analysis. The algorithm is implemented fully in the time domain, which naturally deals with the irregular sampling typical of PTA data and avoids spectral leakage problems associated with frequency domain methods. We take into account the fitting of the timing model, and have generalized our approach to deal with both correlated and uncorrelated colored noise sources. We also develop an incoherent detection statistic that maximizes over all pulsar dependent contributions to the likelihood. To test the effectiveness and sensitivity of our detection statistics, we perform a number of monte-carlo simulations. We produce sensitivity curves for PTAs of various configurations, and outline an implementation of a fully functional data analysis pipeline. Finally, we present a derivation of the likelihood maximized over the gravitational wave phases at the pulsar locations, which results in a vast reduction of the search parameter space.

#### May 18, 2012

1204.4218 (/preprints)
2012-05-18, 18:17 

## [1204.4340] Light scalar field constraints from gravitational-wave observations of compact binaries

Authors: Emanuele Berti, Leonardo Gualtieri, Michael Horbatsch, Justin Alsing

Date: 19 Apr 2012

Abstract: Scalar-tensor theories are among the simplest extensions of general relativity. In theories with light scalars, deviations from Einstein's theory of gravity are determined by the scalar mass m_s and by a Brans-Dicke-like coupling parameter \omega_{BD}. We show that gravitational-wave observations of nonspinning neutron star-black hole binary inspirals can be used to set upper bounds on the combination m_s/\sqrt{\omega_{BD}}. We estimate via a Fisher matrix analysis that individual observations with signal-to-noise ratio \rho would yield (m_s/\sqrt{\omega_{\rm BD}})(\rho/10)\lesssim 10ˆ{-15}, 10ˆ{-16} and 10ˆ{-19} eV for Advanced LIGO, ET and eLISA, respectively. A statistical combination of multiple observations may further improve this bound.

#### May 18, 2012

1204.4340 (/preprints)
2012-05-18, 18:17 

## [1204.4510] Optimizing optical follow-up of gravitational-wave candidates

Authors: Leo Singer, Larry Price, Antony Speranza

Date: 20 Apr 2012

Abstract: Observations with interferometric gravitational-wave detectors result in probability sky maps that are multimodal and spread over 10-100 degˆ2. We present a scheme for maximizing the probability of imaging optical counterparts to gravitational-wave transients given limited observing resources. Our framework is capable of coordinating many telescopes with different fields of view and limiting magnitudes. We present a case study comparing three different planning algorithms. We find that, with the network of telescopes that was used in the most recent joint LIGO-Virgo science run, a relatively straightforward coordinated approach doubles the detection efficiency relative to each telescope observing independently.

#### May 18, 2012

1204.4510 (/preprints)
2012-05-18, 18:15 

## [1205.3112] Treatment of Calibration Uncertainty in Multi-Baseline Cross-Correlation Searches for Gravitational Waves

Authors: John T. Whelan, Emma L. Robinson, Joseph D. Romano, Eric H. Thrane

Date: 14 May 2012

Abstract: Residual uncertainty in the calibration of gravitational wave (GW) detector data leads to systematic errors which must be accounted for in setting limits on the strength of GW signals. When cross-correlation measurements are made using data from a pair of instruments, as in searches for a stochastic GW background, the calibration uncertainties associated with the two instruments can be combined into an uncertainty associated with the pair. With the advent of multi-baseline GW observation (e.g., networks consisting of multiple detectors such as the LIGO observatories and Virgo), a more sophisticated treatment is called for. We describe how the correlations between calibration factors associated with different pairs can be taken into account by marginalizing over the uncertainty associated with each instrument, defining two methods known as per-baseline and per-instrument marginalization.

#### May 18, 2012

1205.3112 (/preprints)
2012-05-18, 18:13 

## [1205.3403] Tidal effects in binary neutron star coalescence

Authors: Sebastiano Bernuzzi, Alessandro Nagar, Marcus Thierfelder, Bernd Bruegmann

Date: 15 May 2012

Abstract: We compare dynamics and waveforms from binary neutron star coalescence as computed by new long-term ($\sim 10$ orbits) numerical relativity simulations and by the tidal effective-one-body (EOB) model including analytical tidal corrections up to second post-Newtonian order (2PN). The current analytical knowledge encoded in the tidal EOB model is found to be sufficient to reproduce the numerical data up to contact and within their uncertainties. Remarkably, no calibration of any tidal EOB free parameters is required, beside those already fitted to binary black holes data. The inclusion of 2PN tidal corrections minimizes the differences with the numerical data, but it is not possible to significantly distinguish them from the leading-order tidal contribution. The presence of a relevant amplification of tidal effects is likely to be excluded, although it can appear as a consequence of numerical inaccuracies. We conclude that the tidally-completed effective-one-body model provides nowadays the most advanced and accurate tool for modelling gravitational waveforms from binary neutron star inspiral up to contact. This work also points out the importance of extensive tests to assess the uncertainties of the numerical data, and the potential need of new numerical strategies to perform accurate simulations.

#### May 18, 2012

1205.3403 (/preprints)
2012-05-18, 18:12 

## [1205.3365] Everything You Always Wanted To Know About The Cosmological Constant Problem (But Were Afraid To Ask)

Authors: Jerome Martin (Institut d&#x27;Astrophysique de Paris)

Date: 15 May 2012

Abstract: This article aims at discussing the cosmological constant problem at a pedagogical but fully technical level. We review how the vacuum energy can be regularized in flat and curved space-time and how it can be understood in terms of Feynman bubble diagrams. In particular, we show that the properly renormalized value of the zero-point energy density today (for a free theory) is in fact far from being 122 orders of magnitude larger than the critical energy density, as often quoted in the literature. We mainly consider the case of scalar fields but also treat the cases of fermions and gauge bosons which allows us to discuss the question of vacuum energy in super-symmetry. Then, we discuss how the cosmological constant can be measured in cosmology and constrained with experiments such as measurements of planet orbits in our solar system or atomic spectra. We also review why the Lamb shift and the Casimir effect seem to indicate that the quantum zero-point fluctuations are not an artifact of the quantum field theory formalism. We investigate how experiments on the universality of free fall can constrain the gravitational properties of vacuum energy and we discuss the status of the weak equivalence principle in quantum mechanics, in particular the Collela, Overhausser and Werner experiment and the quantum Galileo experiment performed with a Salecker-Wigner-Peres clock. Finally, we briefly conclude with a discussion on the solutions to the cosmological constant problem that have been proposed so far.

#### May 18, 2012

1205.3365 (/preprints)
2012-05-18, 18:12 

## [1205.3751] Tests of the universality of free fall for strongly self-gravitating bodies with radio pulsars

Authors: Paulo C. C. Freire, Michael Kramer, Norbert Wex

Date: 16 May 2012

Abstract: In this paper, we review tests of the strong equivalence principle (SEP) derived from binary pulsar data. The extreme difference in binding energy between both components and the precise measurement of the orbital motion provided by pulsar timing allow the only current precision SEP tests for strongly self-gravitating bodies. We start by highlighting why such tests are conceptually important. We then review previous work where limits on SEP violation are obtained with an ensemble of wide binary systems with small eccentricity orbits. Then we propose a new SEP violation test based on the measurement of the variation of the orbital eccentricity de/dt. This new method has the following advantages: a) unlike previous methods it is not based on probabilistic considerations, b) it can make a direct detection of SEP violation, c) the measurement of de/dt is not contaminated by any known external effects, which implies that this SEP test is only restricted by the measurement precision of de/dt. In the final part of the review, we conceptually compare the SEP test with the test for dipolar radiation damping, a phenomenon closely related to SEP violation, and speculate on future prospects by new types of tests in globular clusters and future triple systems.

#### May 18, 2012

1205.3751 (/preprints)
2012-05-18, 18:11 

## [1205.3842] Radiation reaction at 3.5 post-Newtonian order in effective field theory

Date: 17 May 2012

Abstract: We derive the radiation reaction forces on a compact binary inspiral through 3.5 order in the post-Newtonian expansion using the effective field theory approach. We utilize a recent formulation of Hamilton's variational principle that rigorously extends the usual Lagrangian and Hamiltonian formalisms to dissipative systems, including the inspiral of a compact binary from the emission of gravitational waves. We find agreement with previous results, which thus provides a non-trivial confirmation of the extended variational principle. The results from this work nearly complete the equations of motion for the generic inspiral of a compact binary with spinning constituents through 3.5 post-Newtonian order, as derived entirely with effective field theory, with only the spin-orbit corrections to the potential at 3.5 post-Newtonian remaining.

#### May 18, 2012

1205.3842 (/preprints)
2012-05-18, 18:09 

## [1204.6242] The Electromagnetic Signals of Compact Binary Mergers

Authors: T. Piran, E. Nakar, S. Rosswog

Date: 27 Apr 2012

Abstract: Compact binary mergers are prime sources of gravitational waves (GWs), targeted by current and next generation detectors. The question "what is the observable electromagnetic (EM) signature of a compact binary merger?" is an intriguing one with crucial consequences to the quest for gravitational waves. We present a large set of numerical simulations that focus on the electromagnetic signals that emerge from the dynamically ejected sub-relativistic material. These outflows produce on a time scale of a day macronovae - short-lived optical/UV signals powered by radioactive decay. In addition, the outflow interaction with the surrounding matter inevitably leads to a long-lasting radio emission. We calculate the expected radio signals from these outflows on time scales longer than a year, when the sub-relativistic ejecta dominate the emission. We discuss their detectability in 1.4 GHz and 150 MHz and compare it with an updated estimate of the detectability of short GRBs' orphan afterglows. We find that mergers with characteristics similar to those of the Galactic neutron star binary population (similar masses and typical circum-merger Galactic disk density of $1 {\rm cmˆ{-3}}$) that take place at the detection horizon of advanced GW detectors (300 Mpc) yield 1.4 GHz [150 MHz] signals of $\sim 50$ [300] $\mu$Jy, for several years. The signal on time scales of weeks, is dominated by the mildly and/or ultra relativistic outflow, which is not accounted for by our simulations, and is expected to be even brighter. Upcoming all sky surveys are expected to detect a few dozen, and possibly more, merger remnants at any given time thereby providing robust merger rate estimates even before the advanced GW detectors become operational. The macronovae signals from the same distance peak in the optical/UV at an observed magnitude of 22-23 about 10 hours after the merger.

#### May 11, 2012

1204.6242 (/preprints)
2012-05-11, 18:36 

## [1204.6240] The multi-messenger picture of compact object encounters: binary mergers versus dynamical collisions

Authors: S. Rosswog, T. Piran, E. Nakar

Date: 27 Apr 2012

Abstract: We explore the multi-messenger signatures of encounters between two neutron stars and between a neutron star and a stellar-mass black hole. We focus on the differences between gravitational wave driven binary mergers and dynamical collisions that occur, for example, in globular clusters. For both types of encounters we compare the gravitational wave and neutrino emission properties. We also calculate fallback rates and analyze the properties of the dynamically ejected matter. Last but not least we address the electromagnetic transients that accompany each type of encounter.
The canonical nsns merger case ejects more than 1% of a solar mass of extremely neutron-rich ($Y_e\sim 0.03$) material, an amount that is consistent with double neutron star mergers being a major source of r-process in the galaxy. nsbh collisions eject very large amounts of matter ($\sim 0.15$ \msun) which seriously constrains their admissible occurrence rates. The compact object {\em collision} rate must therefore be less, likely much less, than 10% of the nsns {\em merger} rate. The radioactively decaying ejecta produce optical-UV "macronova" which, for the canonical merger case, peak after $\sim 0.4$ days with a luminosity of $\sim 10ˆ{42}$ erg/s. nsns (nsbh) collisions reach up to 3 (7) times larger peak luminosities. The dynamic ejecta deposit a kinetic energy comparable to a supernova in the ambient medium. The canonical merger case releases approximately $2 \times 10ˆ{50}$ erg, the most extreme (but likely rare) cases deposit kinetic energies of up to $10ˆ{52}$ erg. The deceleration of this mildly relativistic material by the ambient medium produces long lasting radio flares. A canonical ns$ˆ2$ merger at the detection horizon of advanced LIGO/Virgo produces a radio flare that peaks on a time scale of one year with a flux of $\sim$0.1 mJy at 1.4 GHz.

#### May 11, 2012

1204.6240 (/preprints)
2012-05-11, 18:36 

## [1204.6739] Cosmology with the lights off: standard sirens in the Einstein Telescope era

Authors: Stephen R. Taylor, Jonathan R. Gair

Date: 30 Apr 2012

Abstract: We explore the prospects for constraining cosmology using gravitational wave (GW) observations of neutron star binaries by the proposed Einstein Telescope (ET), exploiting the narrowness of the neutron star mass function. Double neutron star (DNS) binaries are expected to be one of the first sources detected after "first-light" of Advanced LIGO and are expected to be detected at a rate of a few tens per year in the advanced era. However the proposed Einstein Telescope (ET) could catalogue tens of thousands per year. Combining the measured source redshift distributions with GW-network distance determinations will permit not only the precision measurement of background cosmological parameters, but will provide an insight into the astrophysical properties of these DNS systems. Of particular interest will be to probe the distribution of delay times between DNS-binary creation and subsequent merger, as well as the evolution of the star-formation rate density within ET's detection horizon. Keeping H_0, Omega_{m,0} and Omega_{\Lambda,0} fixed and investigating the precision with which the dark energy equation-of-state parameters could be recovered, we found that with 10ˆ5 detected DNS binaries we could constrain these parameters to an accuracy similar to forecasted constraints from future CMB+BAO+SNIa measurements. Furthermore, modeling the merger delay-time distribution as a power-law, and the star-formation rate (SFR) density as a parametrised version of the Porciani and Madau SF2 model, we find that the associated astrophysical parameters are constrained to within ~ 10%. All parameter precisions scaled as 1/sqrt(N), where N is the number of catalogued detections. We also investigated how precisions varied with the intrinsic underlying properties of the Universe and with the distance reach of the network (which may be affected by the lower frequency cutoff of the detector).

#### May 11, 2012

1204.6739 (/preprints)
2012-05-11, 18:35 

## [1205.1450] The relativistic pulsar-white dwarf binary PSR J1738 0333 II. The most stringent test of scalar-tensor gravity

Authors: Paulo C. C. Freire, Norbert Wex, Gilles Esposito-Far&#xe8;se, Joris P. W. Verbiest, Matthew Bailes, Bryan A. Jacoby, Michael Kramer, Ingrid H. Stairs, John Antoniadis, Gemma H. Janssen

Date: 7 May 2012

Abstract: (abridged) We report the results of a 10-year timing campaign on PSR J1738+0333, a 5.85-ms pulsar in a low-eccentricity 8.5-hour orbit with a low-mass white dwarf companion (…) The measurements of proper motion and parallax allow for a precise subtraction of the kinematic contribution to the observed orbital decay; this results in a significant measurement of the intrinsic orbital decay: (-25.9 +/- 3.2) \times 10ˆ{-15} s/s. This is consistent with the orbital decay from the emission of gravitational waves predicted by general relativity, (-27.7 +1.5/-1.9) \times 10ˆ{-15} s/s (…). This agreement introduces a tight upper limit on dipolar gravitational wave emission, a prediction of most alternative theories of gravity for asymmetric binary systems such as this. We use this limit to derive the most stringent constraints ever on a wide class of gravity theories, where gravity involves a scalar field contribution. When considering general scalar-tensor theories of gravity, our new bounds are more stringent than the best current solar-system limits over most of the parameter space, and constrain the matter-scalar coupling constant {\alpha}_0ˆ2 to be below the 10ˆ{-5} level. For the special case of the Jordan-Fierz-Brans-Dicke, we obtain the one-sigma bound {\alpha}_0ˆ2 < 2 \times 10ˆ{-5}, which is within a factor two of the Cassini limit. We also use our limit on dipolar gravitational wave emission to constrain a wide class of theories of gravity which are based on a generalization of Bekenstein's Tensor-Vector-Scalar gravity (TeVeS), a relativistic formulation of Modified Newtonian Dynamics (MOND).

#### May 11, 2012

1205.1450 (/preprints)
2012-05-11, 17:12 

## [1205.1253] Testing Chern-Simons Modified Gravity with Gravitational-Wave Detections of Extreme-Mass-Ratio Binaries

Authors: Priscilla Canizares (1,2), Jonathan R. Gair (1), Carlos F. Sopuerta (2) ((1) IoA, Cambridge, (2) ICE, CSIC-IEEC)

Date: 6 May 2012

Abstract: [abridged] The detection of gravitational waves from extreme-mass-ratio (EMRI) binaries, comprising a stellar-mass compact object orbiting around a massive black hole, is one of the main targets for low-frequency gravitational-wave detectors in space, like the Laser Interferometer Space Antenna (LISA or eLISA/NGO). The long-duration gravitational-waveforms emitted by such systems encode the structure of the strong field region of the massive black hole, in which the inspiral occurs. The detection and analysis of EMRIs will therefore allow us to study the geometry of massive black holes and determine whether their nature is as predicted by General Relativity and even to test whether General Relativity is the correct theory to describe the dynamics of these systems. To achieve this, EMRI modeling in alternative theories of gravity is required to describe the generation of gravitational waves. In this paper, we explore to what extent EMRI observations with LISA or eLISA/NGO might be able to distinguish between General Relativity and a particular modification of it, known as Dynamical Chern-Simons Modified Gravity. Our analysis is based on a parameter estimation study that uses approximate gravitational waveforms obtained via a radiative-adiabatic method and is restricted to a five-dimensional subspace of the EMRI configuration space. This includes a Chern-Simons parameter that controls the strength of gravitational deviations from General Relativity. We find that, if Dynamical Chern-Simons Modified Gravity is the correct theory, an observatory like LISA or even eLISA/NGO should be able to measure the Chern-Simons parameter with fractional errors below 5%. If General Relativity is the true theory, these observatories should put bounds on this parameter at the level xiˆ(¼) < 10ˆ4 km, which is four orders of magnitude better than current Solar System bounds.

#### May 11, 2012

1205.1253 (/preprints)
2012-05-11, 17:11 

## [1205.1236] Self-force as probe of internal structure

Authors: Soichiro Isoyama, Eric Poisson

Date: 6 May 2012

Abstract: The self-force acting on a (scalar or electric) charge held in place outside a massive body contains information about the body's composition, and can therefore be used as a probe of internal structure. We explore this theme by computing the (scalar or electromagnetic) self-force when the body is a spherical ball of perfect fluid in hydrostatic equilibrium, under the assumption that its rest-mass density and pressure are related by a polytropic equation of state. The body is strongly self-gravitating, and all computations are performed in exact general relativity. The dependence on internal structure is best revealed by expanding the self-force in powers of 1/r, with r denoting the radial position of the charge outside the body. To the leading order, the self-force scales as 1/rˆ3 and depends only on the square of the charge and the body's mass; the leading self-force is universal. The dependence on internal structure is seen at the next order, 1/rˆ5, through a structure factor that depends on the equation of state. We compute this structure factor for relativistic polytropes, and show that for a fixed mass, it increases linearly with the body's radius in the case of the scalar self-force, and quadratically with the body's radius in the case of the electromagnetic self-force. In both cases we find that for a fixed mass and radius, the self-force is smaller if the body is more centrally dense, and larger if the mass density is more uniformly distributed.

#### May 11, 2012

1205.1236 (/preprints)
2012-05-11, 17:11 

## [1205.1124] Swift follow-up observations of candidate gravitational-wave transient events

Date: 5 May 2012

Abstract: We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors and their candidate sky locations were observed by the Swift observatory. Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge". With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.

#### May 11, 2012

1205.1124 (/preprints)
2012-05-11, 17:10 

## [1205.1512] Large-Scale Structure with Gravitational Waves I: Galaxy Clustering

Authors: Donghui Jeong, Fabian Schmidt

Date: 7 May 2012

Abstract: Observed angular positions and redshifts of large-scale structure tracers such as galaxies are affected by gravitational waves through volume distortion and magnification effects. Thus, a gravitational wave background can in principle be probed through clustering statistics of large-scale structure. We calculate the observed angular clustering of galaxies in the presence of a gravitational wave background at linear order including all relativistic effects. For a scale-invariant spectrum of gravitational waves, the effects are most significant at the smallest multipoles (2 <= l <= 5), but typically suppressed by six or more orders of magnitude with respect to scalar contributions for currently allowed amplitudes of the inflationary gravitational wave background. We also discuss the most relevant second-order terms, corresponding to the distortion of tracer correlation functions by gravitational waves. These provide a natural application of the approach recently developed in arXiv:1204.3625.

#### May 11, 2012

1205.1512 (/preprints)
2012-05-11, 17:09 

## [1205.1613] Constraining massive gravity with recent cosmological data

Authors: Vincenzo F. Cardone, Ninfa Radicella, Luca Parisi

Date: 8 May 2012

Abstract: A covariant formulation of a theory with a massive graviton and no negative energy state has been recently proposed as an alternative to the usual General Relativity framework. For a spatially flat homogenous and isotropic universe, the theory introduces modified Friedmann equations where the standard matter term is supplemented by four effective fluids mimicking dust, cosmological constant, quintessence and stiff matter, respectively. We test the viability of this massive gravity formulation by contrasting its theoretical prediction to the Hubble diagram as traced by Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs), the $H(z)$ measurements from passively evolving galaxies, Baryon Acoustic Oscillations (BAOs) from galaxy surveys and the distance priors from the Cosmic Microwave Background Radiation (CMBR) anisotropy spectrum. It turns out that the model is indeed able to very well fit this large dataset thus offering a viable alternative to the usual dark energy framework. We finally set stringent constraints on its parameters also narrowing down the allowed range for the graviton mass.

#### May 11, 2012

1205.1613 (/preprints)
2012-05-11, 17:09 

## [1205.1514] Large-Scale Structure with Gravitational Waves II: Shear

Authors: Fabian Schmidt, Donghui Jeong

Date: 7 May 2012

Abstract: The B-(curl-)mode of the correlation of galaxy ellipticities (shear) can be used to detect a stochastic gravitational wave background, such as that predicted by inflation. In this paper, we derive the tensor mode contributions to shear from both gravitational lensing and intrinsic alignments, using the gauge-invariant, full-sky results of arXiv:1204.3625. We find that the intrinsic alignment contribution, calculated using the linear alignment model, is larger than the lensing contribution by an order of magnitude or more, if the alignment strength for tensor modes is of the same order as for scalar modes. This contribution also extends to higher multipoles. These results make the prospects for probing tensor modes using galaxy surveys less pessimistic than previously thought, though still very challenging.

#### May 11, 2012

1205.1514 (/preprints)
2012-05-11, 17:09 

## [1205.2287] Asymptotic frame selection for binary black hole spacetimes II: Post-Newtonian limit

Authors: Evan Ochsner, Richard O&#x27;Shaughnessy (UWM)

Date: 10 May 2012

Abstract: One way to select a preferred frame from gravitational radiation is via the principal axes of < L L>, an average of the action of rotation group generators on the Weyl tensor at asymptotic infinity. In this paper we evaluate this time-domain average for a quasicircular binary using approximate (post-Newtonian) waveforms. For nonprecessing unequal-mass binaries, we show the dominant eigenvector of this tensor lies along the orbital angular momentum. For precessing binaries, this frame is not generally aligned with either the orbital or total angular momentum, working to leading order in the spins. The difference between these two quantities grows with time, as the binary approaches the end of the inspiral and both precession and higher harmonics become more significant.

#### May 11, 2012

1205.2287 (/preprints)
2012-05-11, 16:56