## [1105.5283] Testing String Theory with Gravitational Waves

Authors: Ruth Durrer, Jasper Hasenkamp

Date: 26 May 2011

Abstract: We provide a simple transfer function that considers the impact of an early matter dominated era on the gravitational wave background and show that string theory can be tested by observations of the gravitational wave background from inflation.

#### May 27, 2011

1105.5283 (/preprints)
2011-05-27, 21:56 

## [1105.4370] Binary Neutron Star Mergers: Dependence on the Nuclear Equation of State

Authors: Kenta Hotokezaka, Koutarou Kyutoku, Hirotada Okawa, Masaru Shibata, Kenta Kiuchi

Date: 22 May 2011

Abstract: We perform a numerical-relativity simulation for the merger of binary neutron stars with 6 nuclear-theory-based equations of state (EOSs) described by piecewise polytropes. Our purpose is to explore the dependence of the dynamical behavior of the binary neutron star merger and resulting gravitational waveforms on the EOS of the supernuclear-density matter. The numerical results show that the merger process and the first outcome are classified into three types; (i) a black hole is promptly formed, (ii) a short-lived hypermassive neutron star (HMNS) is formed, (iii) a long-lived HMNS is formed. The type of the merger depends strongly on the EOS and on the total mass of the binaries. For the EOS with which the maximum mass is larger than 2Msun, the lifetime of the HMNS is longer than 10 ms for a total mass m_0=2.7Msun. A recent radio observation suggests that the maximum mass of spherical neutron stars is M_max \geq 1.97\pm 0.04Msun in one \sigma level. This fact and our results support the possible existence of a HMNS soon after the onset of the merger for a typical binary neutron star with m_0=2.7Msun. We also show that the torus mass surrounding the remnant black hole is correlated with the type of the merger process; the torus mass could be large, \geq 0.1Msun, in the case that a long-lived HMNS is formed. We also show that gravitational waves carry information of the merger process, the remnant, and the torus mass surrounding a black hole.

#### May 23, 2011

1105.4370 (/preprints)
2011-05-23, 22:34 

## [1105.3735] Theoretical Aspects of Massive Gravity

Authors: Kurt Hinterbichler

Date: 18 May 2011

Abstract: Massive gravity has seen a resurgence of interest due to the recent realization that its traditional problems may be overcome, yielding an avenue for addressing important open questions such as the cosmological constant naturalness problem. The possibility of a massive graviton has been studied off and on for the past 70 years. During this time, curiosities such as the vDVZ discontinuity and the Boulware-Deser ghost were uncovered. We re-derive these results in a pedagogical manner, and develop the St\"ukelberg formalism to discuss them from the modern effective field theory viewpoint. We review recent progress of the last decade, including the dissolution of the vDVZ discontinuity via the Vainshtein screening mechanism, the existence of a consistent effective field theory with a stable hierarchy between the graviton mass and the cutoff, the existence of particular interactions which raise the maximal effective field theory cutoff, and strong hints that the higher cutoff theory is ghost free. In addition, we review some peculiarities of massive gravitons on curved space, novel theories in three dimensions, and examples of the emergence of a massive graviton from extra-dimensions and brane worlds.

#### May 23, 2011

1105.3735 (/preprints)
2011-05-23, 22:26 

## [1105.3861] Comparing numerical and analytical calculations of post-ISCO ringdown amplitudes

Authors: Shahar Hadar, Barak Kol, Emanuele Berti, Vitor Cardoso

Date: 19 May 2011

Abstract: We numerically compute the ringdown amplitudes following the plunge of a particle from the innermost stable circular orbit (ISCO) of a Schwarzschild black hole in the extreme-mass ratio limit. We show that the ringdown amplitudes computed in this way are in good agreement with a recent analytical calculation arXiv:0911.3899.

#### May 20, 2011

1105.3861 (/preprints)
2011-05-20, 13:48 

## [1105.3567] The importance of including small body spin effects in the modelling of extreme and intermediate mass-ratio inspirals

Authors: EA Huerta, Jonathan R Gair

Date: 18 May 2011

Abstract: We explore the ability of future low-frequency gravitational wave detectors to measure the spin of stellar mass and intermediate mass black holes that inspiral onto super-massive Kerr black holes (SMBHs). We develop a kludge waveform model based on the equations of motion derived by Saijo et al. [Phys Rev D 58, 064005, 1998] for spinning BH binaries, augmented with spin-orbit and spin-spin couplings taken from perturbative and post-Newtonian (PN) calculations, and the associated conservative self-force corrections, derived by comparison to PN results. We model the inspiral phase using accurate fluxes which include perturbative corrections for the spin of the inspiralling body, spin-spin couplings and higher-order fits to solutions of the Teukolsky equation. We present results of Monte Carlo simulations of parameter estimation errors and of the model errors that arise when we omit conservative corrections from the waveform template. For a source 5000+10ˆ6 solar mass observed with an SNR of 1000, LISA will be able to determine the two masses to within a fractional error of ~0.001, measure the SMBH spin magnitude, q, and the spin magnitude of the inspiralling BH to 0.0001, 10%, respectively, and determine the location of the source in the sky and the SMBH spin orientation to within 0.0001 steradians. For a 10+10ˆ6 solar mass system observed with SNR of 30, LISA will not be able to determine the spin magnitude of the inspiralling BH, although the measurement of the other waveform parameters is not significantly degraded by the presence of spin. The model errors which arise from ignoring conservative corrections become significant for mass-ratios above 0.0001, but including these corrections up to 2PN order may be sufficient to reduce these systematic errors to an acceptable level.

#### May 19, 2011

1105.3567 (/preprints)
2011-05-19, 15:25 

## [1105.3191] A Metric for Rapidly Spinning Black Holes Suitable for Strong-Field Tests of the No-Hair Theorem

Authors: Tim Johannsen, Dimitrios Psaltis (Arizona)

Date: 16 May 2011

Abstract: According to the no-hair theorem, astrophysical black holes are uniquely characterized by their masses and spins and are described by the Kerr metric. Several parametric deviations from the Kerr metric have been suggested to study observational signatures in both the electromagnetic and gravitational-wave spectra that differ from the expected Kerr signals. Due to the no-hair theorem, however, such spacetimes cannot be regular everywhere outside the event horizons, if they are solutions to the Einstein field equations; they are often characterized by naked singularities or closed time-like loops in the regions of the spacetime that are accessible to an external observer. For observational tests of the no-hair theorem that involve phenomena in the vicinity of the circular photon orbit or the innermost stable circular orbit around a black hole, these pathologies limit the applicability of the metrics only to compact objects that do not spin rapidly. In this paper, we construct a Kerr-like metric which depends on a set of free parameters in addition to its mass and spin and which is regular everywhere outside of the event horizon. We derive expressions for the energy and angular momentum of a particle on a circular equatorial orbit around the black hole and compute the locations of the innermost stable circular orbit and the circular photon orbit. We demonstrate that these orbits change significantly for even moderate deviations from the Kerr metric. The properties of our metric make it an ideally suited spacetime to carry out strong-field tests of the no-hair theorem in the electromagnetic spectrum using the properties of accretion flows around astrophysical black holes of arbitrary spin.

#### May 18, 2011

1105.3191 (/preprints)
2011-05-18, 14:51 

## [1105.1678] Gravitational waves from perturbed stars

Authors: Valeria Ferrari

Date: 9 May 2011

Abstract: Non radial oscillations of neutron stars are associated with the emission of gravitational waves. The characteristic frequencies of these oscillations can be computed using the theory of stellar perturbations, and they are shown to carry detailed information on the internal structure of the emitting source. Moreover, they appear to be encoded in various radiative processes, as for instance in the tail of the giant flares of Soft Gamma Repeaters. Thus, their determination is central to the theory of stellar perturbation. A viable approach to the problem consists in formulating this theory as a problem of resonant scattering of gravitational waves incident on the potential barrier generated by the spacetime curvature. This approach discloses some unexpected correspondences between the theory of stellar perturbations and the theory of quantum mechanics, and allows us to predict new relativistic effects.

#### May 17, 2011

1105.1678 (/preprints)
2011-05-17, 14:42 

## [1105.2125] Gravitational waves and neutrino emission from the merger of binary neutron stars

Authors: Yuichiro Sekiguchi, Kenta Kiuchi, Koutarou Kyutoku, Masaru Shibata

Date: 11 May 2011

Abstract: Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating a finite-temperature (Shen's) equation of state (EOS) and neutrino cooling for the first time. It is found that for this stiff EOS, a hypermassive neutron star (HMNS) with a long lifetime ($\gg 10$ ms) is the outcome for the total mass $\alt 3.0M_{\odot}$. It is shown that the typical total neutrino luminosity of the HMNS is $\sim 3$--$8\times 10ˆ{53}$ ergs/s and the effective amplitude of gravitational waves from the HMNS is 4--$6 \times 10ˆ{-22}$ at $f=2.1$--2.5 kHz for a source distance of 100 Mpc. We also present the neutrino luminosity curve when a black hole is formed for the first time.

#### May 17, 2011

1105.2125 (/preprints)
2011-05-17, 14:41 

## [1105.2088] Gravitational Wave Tests of General Relativity with the Parameterized Post-Einsteinian Framework

Authors: Neil Cornish, Laura Sampson, Nico Yunes, Frans Pretorius

Date: 11 May 2011

Abstract: Gravitational wave astronomy has tremendous potential for studying extreme astrophysical phenomena and exploring fundamental physics. The waves produced by binary black hole mergers will provide a pristine environment in which to study strong field, dynamical gravity. Extracting detailed information about these systems requires accurate theoretical models of the gravitational wave signals. If gravity is not described by General Relativity, analyses that are based on waveforms derived from Einstein's field equations could result in parameter biases and a loss of detection efficiency. A new class of "parameterized post-Einsteinian" (ppE) waveforms has been proposed to cover this eventuality. Here we apply the ppE approach to simulated data from a network of advanced ground based interferometers (aLIGO/aVirgo) and from a future spaced based interferometer (LISA). Bayesian inference and model selection are used to investigate parameter biases, and to determine the level at which departures from general relativity can be detected. We find that in some cases the parameter biases from assuming the wrong theory can be severe. We also find that gravitational wave observations will beat the existing bounds on deviations from general relativity derived from the orbital decay of binary pulsars by a large margin across a wide swath of parameter space.

#### May 17, 2011

1105.2088 (/preprints)
2011-05-17, 14:41 

## [1105.3184] Localizing compact binary inspirals on the sky using ground-based gravitational wave interferometers

Authors: Samaya M. Nissanke, Jonathan L. Sievers, Neal Dalal, Daniel E. Holz

Date: 16 May 2011

Abstract: The inspirals and mergers of compact binaries are among the most promising events for ground-based gravitational wave (GW) observatories. The detection of electromagnetic (EM) signals from these sources would provide complementary information to the GW signal. It is therefore important to determine the ability of gravitational-wave detectors to localize compact binaries on the sky, so that they can be matched to their EM counterparts. We use Markov Chain Monte Carlo techniques to study sky localization using networks of ground-based interferometers. Using a coherent-network analysis, we find that the LIGO-Virgo network can localize 50% of their ~8 sigma detected neutron star binaries to better than 50 sq.deg. with 95% confidence region. The addition of LCGT and LIGO-Australia improves this to 12 sq.deg.. Using a more conservative coincident detection threshold, we find that 50% of detected neutron star binaries are localized to 13 sq.deg. using the LIGO-Virgo network, and to 3 sq.deg. using the LIGO-Virgo-LCGT-LIGO-Australia network. Our findings suggest that the coordination of GW observatories and EM facilities offers great promise.

#### May 17, 2011

1105.3184 (/preprints)
2011-05-17, 14:09 

## [1105.2959] Equatorial circular motion in Kerr spacetime

Authors: Daniela Pugliese, Hernando Quevedo, Remo Ruffini

Date: 15 May 2011

Abstract: We analyze the properties of circular orbits of test particles on the equatorial plane of a rotating central mass whose gravitational field is described by the Kerr spacetime. For rotating black holes and naked singularities we explore all the spatial regions where circular orbits can exist and analyze the behavior of the energy and the angular momentum of the corresponding test particles. In particular, we find all the radii at which a test particle can have zero angular momentum due to the repulsive gravity effects generated by naked singularities. We classify all the stability zones of circular orbits. It is shown that the geometric structure of the stability zones of black holes is completely different from that of naked singularities.

#### May 17, 2011

1105.2959 (/preprints)
2011-05-17, 14:08 

## [1105.3175] Eccentric Black Hole-Neutron Star Mergers

Authors: Branson C. Stephens (1), William E. East (2), Frans Pretorius (2) ((1) UW-Milwaukee, (2) Princeton University)

Date: 16 May 2011

Abstract: Within the next few years gravitational waves (GWs) from merging black holes (BHs) and neutron stars (NSs) may be directly detected, making a thorough theoretical understanding of these systems a high priority. Such mergers are expected to result from primordial, quasi-circular BH-NS inspiral as well as dynamically formed capture binaries. The latter channel allows mergers with high eccentricity, resulting in a richer variety of outcomes. We perform general relativistic simulations of BH-NS interactions with a range of impact parameters, and find significant variation in the properties of these events that have potentially observable consequences, namely the GW signature, remnant accretion disk mass, and amount of unbound material.

#### May 17, 2011

1105.3175 (/preprints)
2011-05-17, 14:08 

## [1105.2821] Binary black hole mergers in gaseous disks: Simulations in general relativity

Authors: Brian D. Farris, Yuk Tung Liu, Stuart L. Shapiro

Date: 13 May 2011

#### May 02, 2011

1104.5615 (/preprints)
2011-05-02, 13:56 

## [1104.5659] Tail-induced spin-orbit effect in the gravitational radiation of compact binaries

Authors: Luc Blanchet (IAP), Alessandra Buonanno, Guillaume Faye (IAP)

Date: 29 Apr 2011

Abstract: Gravitational waves contain tail effects which are due to the back-scattering of linear waves in the curved space-time geometry around the source. In this paper we improve the knowledge and accuracy of the two-body inspiraling post-Newtonian (PN) dynamics and gravitational-wave signal by computing the spin-orbit terms induced by tail effects. Notably, we derive those terms at 3PN order in the gravitational-wave energy flux, and 2.5PN and 3PN orders in the wave polarizations. This is then used to derive the spin-orbit tail effects in the phasing through 3PN order. Our results can be employed to carry out more accurate comparisons with numerical-relativity simulations and to improve the accuracy of analytical templates aimed at describing the all process of inspiral, merger and ringdown.

#### May 02, 2011

1104.5659 (/preprints)
2011-05-02, 13:55