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Harte A.I.,Max Planck Institute For Gravitationsphysik
Classical and Quantum Gravity | Year: 2012

The external or bulk motion of extended bodies is studied in general relativity. Compact material objects of essentially arbitrary shape, spin, internal composition and velocity are allowed as long as there is no direct (non-gravitational) contact with other sources of stress-energy. Physically reasonable linear and angular momenta are proposed for such bodies and exact equations describing their evolution are derived. Changes in the momenta depend on a certain effective metric that is closely related to a non-perturbative generalization of the Detweiler-Whiting R-field originally introduced in the self-force literature. If the effective metric inside a self-gravitating body can be adequately approximated by an appropriate power series, the instantaneous gravitational force and torque exerted on it is shown to be identical to the force and torque exerted on an appropriate test body moving in the effective metric. This result holds to all multipole orders. The only instantaneous effect of a bodys self-field is to finitely renormalize the bare multipole moments of its stress-energy tensor. The MiSaTaQuWa expression for the gravitational self-force is recovered as a simple application. A gravitational self-torque is obtained as well. Lastly, it is shown that the effective metric in which objects appear to move is approximately a solution to the vacuum Einstein equation if the physical metric is an approximate solution to Einsteins equation linearized about a vacuum background. © 2012 IOP Publishing Ltd.

Virmani A.,Max Planck Institute For Gravitationsphysik
Journal of High Energy Physics | Year: 2012

We consider the rotating non-extremal black hole of N=2 D=4 STU supergravity carrying three magnetic charges and one electric charge. We show that its subtracted geometry is obtained by applying a specific SO(4,4) Harrison transformation on the black hole. As previously noted, the resulting subtracted geometry is a solution of the N=2 S=T=U supergravity. © SISSA 2012.

Ohme F.,Max Planck Institute For Gravitationsphysik
Classical and Quantum Gravity | Year: 2012

Models of gravitational waveforms from coalescing black-hole binaries play a crucial role in the efforts to detect and interpret the signatures of those binaries in the data of large-scale interferometers. Here we summarize recent models that combine information both from analytical approximations and numerical relativity. We briefly lay out and compare the strategies employed to build such complete models and we recapitulate the errors associated with various aspects of the modelling process. © 2012 IOP Publishing Ltd.

Hinder I.,Max Planck Institute For Gravitationsphysik
Classical and Quantum Gravity | Year: 2010

Since the breakthroughs in 2005 which have led to long-term stable solutions of the binary black hole problem in numerical relativity, much progress has been made. I present here a short summary of the state of the field, including the capabilities of numerical relativity codes, recent physical results obtained from simulations and improvements to the methods used to evolve and analyse binary black hole spacetimes. © 2010 IOP Publishing Ltd.

Sesana A.,Max Planck Institute For Gravitationsphysik
Classical and Quantum Gravity | Year: 2013

Pulsar timing arrays (PTAs) are designed to detect the predicted gravitational wave (GW) background produced by a cosmological population of supermassive black hole (SMBH) binaries. In this contribution, I review the physics of such GW background, highlighting its dependence on the overall binary population, the relation between SMBHs and their hosts, and their coupling with the stellar and gaseous environment. The latter is particularly relevant when it drives the binaries to extreme eccentricities (e > 0.9), which might be the case for stellar-driven systems. This causes a substantial suppression of the low-frequency signal, potentially posing a serious threat to the effectiveness of PTA observations. A future PTA detection will allow us to directly observe for the first time subparsec SMBH binaries on their way to the GW-driven coalescence, providing important answers of the outstanding questions related to the physics underlying the formation and evolution of these spectacular sources. © 2013 IOP Publishing Ltd.

Vartanov G.S.,Max Planck Institute For Gravitationsphysik
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

In this Letter we would like to apply the superconformal index technique to give one more evidence for the theory proposed by Intriligator, Seiberg and Shenker (ISS) as being described by interacting conformal field theory in its IR fixed point. © 2010.

Friedrich H.,Max Planck Institute For Gravitationsphysik
Classical and Quantum Gravity | Year: 2014

We discuss the notion of stability and the choice of boundary conditions for AdS-type space-times and point out difficulties in the construction of Cauchy data which arise if reflective boundary conditions are imposed. © 2014 IOP Publishing Ltd.

Bentivegna E.,Max Planck Institute For Gravitationsphysik
Classical and Quantum Gravity | Year: 2014

Novel applications of Numerical Relativity demand more flexible algorithms and tools. In this paper, I develop and test a multigrid solver, based on the infrastructure provided by the Einstein Toolkit, for elliptic partial differential equations on spaces with periodic boundary conditions (PBCs). This type of boundary often characterizes the numerical representation of cosmological models, where space is assumed to be made up of identical copies of a single fiducial domain, so that only a finite volume (with PBCs at its edges) needs to be simulated. After a few tests and comparisons with existing codes, I use the solver to generate initial data for an infinite, periodic, cubic black-hole lattice. © 2014 IOP Publishing Ltd.

Fuchs E.,Max Planck Institute For Gravitationsphysik | Kroyter M.,Max Planck Institute For Gravitationsphysik
Physics Reports | Year: 2011

In this work, we review Schnabl's construction of the tachyon vacuum solution to bosonic covariant open string field theory and the results that followed. We survey the state of the art of string field theory research preceding this construction focusing on Sen's conjectures and the results obtained using level truncation methods. The tachyon vacuum solution can be described in various ways. We describe its geometric representation using wedge states, its formal algebraic representation as a pure-gauge solution and its oscillator representation. We also describe the analytical proofs of some of Sen's conjectures for this solution.The tools used in the context of the vacuum solution can be adapted to the construction of other solutions, namely various marginal deformations. We present some of the approaches used in the construction of these solutions.The generalization of these ideas to open superstring field theory is explained in detail. We start from the exposition of the problems one faces in the construction of superstring field theory. We then present the cubic and the non-polynomial versions of superstring field theory and discuss a proposal suggesting their classical equivalence. Finally, the bosonic solutions are generalized to this case. In particular, we focus on the (somewhat surprising) generalization of the tachyon solution to the case of a theory with no tachyons. © 2011 Elsevier B.V.

Sesana A.,Max Planck Institute For Gravitationsphysik
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

In this Letter, we carry out the first systematic investigation of the expected gravitational wave (GW) background generated by supermassive black hole (SMBH) binaries in the nHz frequency band accessible to pulsar timing arrays (PTAs). We take from the literature several estimates of the redshift-dependent galaxy mass function and of the fraction of close galaxy pairs to derive a wide range of galaxy merger rates. We then exploit empirical black hole- host relations to populate merging galaxies with SMBHs. The result of our procedure is a collection of a large number of phenomenological SMBH binary merger rates consistent with current observational constraints on the galaxy assembly at z < 1.5. For each merger rate we compute the associated GW signal, eventually producing a large set of estimates of the nHz GW background that we use to infer confidence intervals of its expected amplitude. When considering the most recent SMBH-host relations, accounting for overmassive black holes in brightest cluster galaxies, we find that the nominal 1σ interval of the expected GW signal is only a factor of 3-10 below current PTA limits, implying a non-negligible chance of detection in the next few years.© 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.

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