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Showing papers in "Classical and Quantum Gravity in 2013"


Journal ArticleDOI
TL;DR: In this paper, the cosmological dynamics of quintessence are reviewed, paying particular attention to the evolution of the dark energy equation of state w. The authors derive an analytic formula for the growth rate of matter density perturbations in dynamical dark energy models, which allows a possibility of putting further bounds on w from the measurement of redshift-space distortions in the galaxy power spectrum.
Abstract: Quintessence is a canonical scalar field introduced to explain the late-time cosmic acceleration. The cosmological dynamics of quintessence is reviewed, paying particular attention to the evolution of the dark energy equation of state w. For the field potentials having tracking and thawing properties, the evolution of w can be known analytically in terms of a few model parameters. Using the analytic expression of w, we constrain quintessence models from the observations of supernovae type Ia, cosmic microwave background and baryon acoustic oscillations. The tracking freezing models are hardly distinguishable from the Λ-cold-dark-matter model, whereas in thawing models the today's field equation of state is constrained to be w0 < −0.7 (95% CL). We also derive an analytic formula for the growth rate of matter density perturbations in dynamical dark energy models, which allows a possibility of putting further bounds on w from the measurement of redshift-space distortions in the galaxy power spectrum. Finally, we review particle physics models of quintessence—such as those motivated by supersymmetric theories. The field potentials of thawing models based on a pseudo-Nambu–Goldstone boson or extended supergravity theories have a nice property that a tiny mass of quintessence can be protected against radiative corrections.

528 citations


Journal ArticleDOI
TL;DR: In this paper, the Vainshtein mechanism is introduced to hide via nonlinear effects, typically for source distances smaller than a so-called Vainsshtein radius which depends on the source and on the theory considered.
Abstract: We introduce the Vainshtein mechanism which plays a crucial role in massive gravities, as well as in related theories such as Galileons and their extensions. This mechanism, also known as k-mouflage, allows to hide via nonlinear effects—typically for source distances smaller than a so-called Vainshtein radius which depends on the source and on the theory considered—some degrees of freedom whose effects are then only left important at large distances, e.g. for cosmology. It is introduced here in nonlinear Fierz–Pauli theories (massive gravities), including the dRGT theories, in their decoupling limits, as well as in other models such as the DGP model or generalized Galileons. This presentation is self-contained, and before discussing the Vainshtein mechanism we introduce some useful results and concepts concerning massive gravity, such as the vDVZ discontinuity, the decoupling limits or the Boulware–Deser ghost.

432 citations


Journal ArticleDOI
TL;DR: Double field theory (DFT) as discussed by the authors is a generalization of string theory that incorporates T-duality as a symmetry of a field theory defined on a double configuration space.
Abstract: Double field theory (DFT) is a proposal to incorporate T-duality, a distinctive symmetry of string theory, as a symmetry of a field theory defined on a double configuration space. The aim of this review is to provide a pedagogical presentation of DFT and its applications. We first introduce some basic ideas on T-duality and supergravity in order to proceed to the construction of generalized diffeomorphisms and an invariant action on the double space. Steps towards the construction of a geometry on the double space are discussed. We then address generalized Scherk–Schwarz compactifications of DFT and their connection to gauged supergravity and flux compactifications. We also discuss U-duality extensions and present a brief parcours on worldsheet approaches to DFT. Finally, we provide a summary of other developments and applications that are not discussed in detail in the review.

429 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an updated review of Lorentz invariance tests in effective field theories (EFTs) in the matter as well as in the gravity sector.
Abstract: We present an updated review of Lorentz invariance tests in effective field theories (EFTs) in the matter as well as in the gravity sector. After a general discussion of the role of Lorentz invariance and a derivation of its transformations along the so-called von Ignatovski theorem, we present the dynamical frameworks developed within local EFT and the available constraints on the parameters governing the Lorentz breaking effects. In the end, we discuss two specific examples: the OPERA ‘affaire’ and the case of Hořava–Lifshitz gravity. The first case will serve as an example, and a caveat, of the practical application of the general techniques developed for constraining Lorentz invariance violation to a direct observation potentially showing these effects. The second case will show how the application of the same techniques to a specific quantum gravity scenario has far-reaching implications not foreseeable in a purely phenomenological EFT approach.

414 citations


Journal ArticleDOI
TL;DR: In this paper, the authors consider three-dimensional conformal field theories that have a higher spin symmetry that is slightly broken and constrain the three-point functions of the theories to a leading order in N. They show that there are two families of solutions.
Abstract: We consider three-dimensional conformal field theories that have a higher spin symmetry that is slightly broken. The theories have a large-N limit in the sense that the operators separate into single trace and multitrace and obey the usual large-N factorization properties. We assume that the spectrum of single trace operators is similar to the one that one obtains in the Vasiliev theories. Namely the only single trace operators are the higher spin currents plus an additional scalar. The anomalous dimensions of the higher spin currents are of the order 1/N. Using the slightly broken higher spin symmetry, we constrain the three-point functions of the theories to a leading order in N. We show that there are two families of solutions. One family can be realized as a theory of N fermions with an O(N) Chern?Simons gauge field, the other as an N bosons plus the Chern?Simons gauge field. The family of solutions is parametrized by the 't Hooft coupling. At special parity preserving points, we obtain the critical O(N) models: the Wilson?Fisher one and the Gross?Neveu one. Our analysis also fixes the on-shell three-point functions of Vasiliev's theory on AdS4 or dS4.

367 citations


Journal ArticleDOI
TL;DR: The European Pulsar Timing Array (EPTA) and the Large European Array for Pulsars (LEAP) play crucial roles in the global effort to detect gravitational waves (GWs) with a PTA experiment.
Abstract: The European Pulsar Timing Array (EPTA) and the Large European Array for Pulsars (LEAP) play crucial roles in the global effort to detect gravitational waves (GWs) with a Pulsar Timing Array (PTA) experiment. While the EPTA uses five of the world’s largest cm-radio telescopes, LEAP harvests their combined power to synthesize a 194 m equivalent dish to provide high-precision PTA data for most of the sky. The EPTA has already produced a large variety of results, including astrophysical studies of individual pulsars, tests of theories of gravity, stringent limits on a GW background produced by super-massive binary black holes or the vibration of cosmic strings. It has also undertaken the development of new analysis methods and techniques, and studies of the astrophysics and population of expected GW background sources. This review gives an overview of the EPTA and LEAP set-ups and corresponding activities.

304 citations


Journal ArticleDOI
TL;DR: The North American Nanohertz Observatory for Gravitational Waves (NANOW) is a collaboration of researchers who are actively engaged in using North American radio telescopes to detect and study gravitational waves (GWs) via pulsar timing.
Abstract: The North American Nanohertz Observatory for Gravitational Waves is a collaboration of researchers who are actively engaged in using North American radio telescopes to detect and study gravitational waves (GWs) via pulsar timing. To achieve this goal, we regularly observe millisecond pulsars with the Arecibo and Green Bank telescopes and develop and implement new instrumentation and algorithms for searching for and observing pulsars, calculating arrival times, understanding and correcting for propagation delays and sources of noise in our data and detecting and characterizing a variety of GW sources. We collaborate on these activities with colleagues in the International Pulsar Timing Array. We also educate students of all levels and the public about the detection and study of GWs via pulsar timing.

258 citations


Journal ArticleDOI
TL;DR: In this paper, a self consistent extension of the inflationary paradigm over the 11 orders of magnitude in density and curvature, from the big bounce to the onset of slow roll, is presented.
Abstract: Using techniques from loop quantum gravity, the standard theory of cosmological perturbations was recently generalized to encompass the Planck era. We now apply this framework to explore pre-inflationary dynamics. The framework enables us to isolate and resolve the true trans-Planckian difficulties, with interesting lessons both for theory and observations. Specifically, for a large class of initial conditions at the bounce, we are led to a self consistent extension of the inflationary paradigm over the 11 orders of magnitude in density and curvature, from the big bounce to the onset of slow roll. In addition, for a narrow window of initial conditions, there are departures from the standard paradigm, with novel effects—such as a modification of the consistency relation between the ratio of the tensor to scalar power spectrum and the tensor spectral index, as well as a new source for non-Gaussianities—which could extend the reach of cosmological observations to the deep Planck regime of the early universe. Communicated by P Singh

239 citations


Journal ArticleDOI
TL;DR: In this article, a set of self-similar equations for the null-slicing form of the metric which we are using for our numerical calculations are derived, and compared with the results obtained by integrating these with the ones coming from our simulations for the collapse of cosmological perturbations within an expanding universe.
Abstract: Following on after three previous papers discussing the formation of primordial black holes during the radiative era of the early universe, we present here a further investigation of the critical nature of the process involved, aimed at making contact with some of the basic underlying ideas from the literature on critical collapse. We focus on the intermediate state, which we have found appearing in cases with perturbations close to the critical limit, and examine the connection between this and the similarity solutions which play a fundamental role in the standard picture of critical collapse. We have derived a set of self-similar equations for the null-slicing form of the metric which we are using for our numerical calculations, and have then compared the results obtained by integrating these with the ones coming from our simulations for the collapse of cosmological perturbations within an expanding universe. We find that the similarity solution is asymptotically approached in a region which grows to cover both the contracting matter and part of the semi-void which forms outside it. Our main interest is in the situation relevant for primordial black hole formation in the radiative era of the early universe, where the relation between the pressure p and the energy density e can be reasonably approximated by an expression of the form p = we with w = 1/3. However, we have also looked at other values of w, both because these have been considered in the previous literature and also because they can be helpful for giving further insight into situations relevant for primordial black hole formation. As in our previous work, we have started our simulations with initial supra-horizon scale perturbations of a type which could have come from inflation.

230 citations


Journal ArticleDOI
TL;DR: In this paper, an axion with a shift symmetry is used to ensure a prolonged slow-roll background evolution, which can explain why two or more terms in the potential are ne-tuned against each other, as needed for typical models of small-eld ination.
Abstract: Because the inationary mechanism is extremely sensitive to UV-physics, the construction of theoretically robust models of ination provides a unique window on Planck-scale physics. We review eorts to use an axion with a shift symmetry to ensure a prolonged slow-roll background evolution. The symmetry dictates which operators are allowed, and these in turn determine the observational predictions of this class of models, which include observable gravitational waves (potentially chiral), oscillations in all primordial correlators, specic deviations from scale invariance and Gaussianity and primordial black holes. We discuss the constraints on this class of models in light of the recent Planck results and comment on future perspectives. The shift symmetry is very useful in models of large-eld ination, which typically have monomial potentials, but it cannot explain why two or more terms in the potential are ne-tuned against each other, as needed for typical models of small-eld ination.

217 citations


Journal ArticleDOI
TL;DR: The International Pulsar Timing Array (IPTA) as mentioned in this paper is an organization whose raison d'etre is to facilitate collaboration between the three main existing PTAs in order to realize the benefits of combined PTA data sets in reaching the goals of PTA projects.
Abstract: The International Pulsar Timing Array (IPTA) is an organization whose raison d’etre is to facilitate collaboration between the three main existing PTAs (the EPTA in Europe, NANOGrav in North America and the PPTA in Australia) in order to realize the benefits of combined PTA data sets in reaching the goals of PTA projects. Currently, shared data sets for 50 pulsars are available for IPTA-based projects. Operation of the IPTA is administered by a Steering Committee consisting of six members, two from each PTA, plus the immediate past Chair in a non-voting capacity. A Constitution and several Agreements define the framework for the collaboration. Web pages provide information both to members of participating PTAs and to the general public. With support from an NSF PIRE grant, the IPTA facilitates the organization of annual Student Workshops and Science Meetings. These are very valuable both in training new students and in communicating current results from IPTA-based research.

Journal ArticleDOI
TL;DR: The Parkes Pulsar Timing Array project as discussed by the authors was proposed to make a direct detection of gravitational waves, improve the solar system planetary ephemeris and develop a pulsar-based timescale.
Abstract: The aims of the Parkes Pulsar Timing Array project are to (1) make a direct detection of gravitational waves, (2) improve the solar system planetary ephemeris and (3) develop a pulsar-based timescale. In this paper we describe the project, explain how the data are collected and processed and describe current research. Our current data sets are able to place an upper bound on the gravitational wave background that is the most stringent to date.

Journal ArticleDOI
TL;DR: In this paper, the authors review different constructions of Galileon theories in both flat and curved space, and for both single scalar field models as well as multifield models, focusing on the formal mathematical properties of these theories and their construction.
Abstract: We review different constructions of Galileon theories in both flat and curved space, and for both single scalar field models as well as multifield models. Our main emphasis is on the formal mathematical properties of these theories and their construction.

Journal ArticleDOI
TL;DR: In this article, it was shown that the physical wavelength of fluctuations which are studied at the present time by means of cosmological observations may well originate with a wavelength smaller than the Planck length at the beginning of the inflationary phase.
Abstract: The accelerated expansion of space during the cosmological inflation period leads to trans-Planckian issues which need to be addressed. Most importantly, the physical wavelength of fluctuations which are studied at the present time by means of cosmological observations may well originate with a wavelength smaller than the Planck length at the beginning of the inflationary phase. Thus, questions arise as to whether the usual predictions of inflationary cosmology are robust considering our ignorance of physics on trans-Planckian scales, and whether the imprints of Planck-scale physics are at the present time observable. These and other related questions are reviewed in this paper.

Journal ArticleDOI
TL;DR: In this article, the authors derived scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and showed that the large power-law increase of the signal to noise ratio as a function of the observation time T that is usually assumed holds only at early times.
Abstract: We derive scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and show that the large power-law increase of the signal-to-noise ratio as a function of the observation time T that is usually assumed holds only at early times. After enough time has elapsed, pulsar timing arrays enter a new regime where the signal to noise only scales as . In addition, in this regime the quality of the pulsar timing data and the cadence become relatively unimportant. This occurs because the lowest frequencies of the pulsar timing residuals become gravitational-wave dominated. Pulsar timing arrays enter this regime more quickly than one might naively suspect. For T = 10 yr observations and typical stochastic background amplitudes, pulsars with residual root-mean-squares of less than about 1 μs are already in that regime. The best strategy to increase the detectability of the background in this regime is to increase the number of pulsars in the array. We also perform realistic simulations of the NANOGrav pulsar timing array, which through an aggressive pulsar survey campaign adds new millisecond pulsars regularly to its array, and show that a detection is possible within a decade, and could occur as early as 2016.

Journal ArticleDOI
TL;DR: The Higgs field of the pure Standard Model can lead to the inflationary expansion of the early Universe if it is non-minimally coupled to gravity as discussed by the authors, and the model predicts Cosmic Microwave Background (CMB) parameters in perfect agreement with the current observations.
Abstract: The Higgs field of the pure Standard Model can lead to the inflationary expansion of the early Universe if it is non-minimally coupled to gravity. The model predicts Cosmic Microwave Background (CMB) parameters in perfect agreement with the current observations and has implications for the Higgs boson mass. We review the model, its predictions, problems arising with its quantization and some closely related models.

Journal ArticleDOI
TL;DR: In this paper, an electromagnetic analogue of gravitational wave memory is presented, where the authors consider what change has occurred to a detector of electromagnetic radiation after the wave has passed rather than a distortion in the detector, as occurs in the gravitational wave case.
Abstract: We present an electromagnetic analogue of gravitational wave memory That is, we consider what change has occurred to a detector of electromagnetic radiation after the wave has passed Rather than a distortion in the detector, as occurs in the gravitational wave case, we find a residual velocity (a ‘kick’) to the charges in the detector In analogy with the two types of gravitational wave memory (‘ordinary’ and ‘nonlinear’) we find two types of electromagnetic kick

Journal ArticleDOI
TL;DR: In this paper, the authors review the current understanding of the physical properties of Sagittarius A*, with a particular emphasis on the radio properties, the black hole shadow, and models for the emission and appearance of the source.
Abstract: The center of our Galaxy hosts the best constrained supermassive black hole in the universe, Sagittarius A* (Sgr A*). Its mass and distance have been accurately determined from stellar orbits and proper motion studies, respectively, and its high-frequency radio, and highly variable near-infrared and x-ray emission originate from within a few Schwarzschild radii of the event horizon. The theory of general relativity (GR) predicts the appearance of a black hole shadow, which is a lensed image of the event horizon. This shadow can be resolved by very long baseline radio interferometry and test basic predictions of GR and alternatives thereof. In this paper we review our current understanding of the physical properties of Sgr A*, with a particular emphasis on the radio properties, the black hole shadow, and models for the emission and appearance of the source. We argue that the Galactic Center holds enormous potential for experimental tests of black hole accretion and theories of gravitation in their strong limits.

Journal ArticleDOI
TL;DR: In this paper, a review of how GWs will improve our understanding of gamma-ray burst central engines, their astrophysical formation channels and the prospects and methods for different search strategies.
Abstract: By reaching through shrouding blastwaves, efficiently discovering off-axis events and probing the central engine at work, gravitational wave (GW) observations will soon revolutionize the study of gamma-ray bursts. Already, analyses of GW data targeting gamma-ray bursts have helped constrain the central engines of selected events. Advanced GW detectors with significantly improved sensitivities are under construction. After outlining the GW emission mechanisms from gamma-ray burst progenitors (binary coalescences, stellar core collapses, magnetars and others) that may be detectable with advanced detectors, we review how GWs will improve our understanding of gamma-ray burst central engines, their astrophysical formation channels and the prospects and methods for different search strategies. We place special emphasis on multimessenger searches. To achieve the most scientific benefit, GW, electromagnetic and neutrino observations should be combined to provide greater discriminating power and science reach.

Journal ArticleDOI
TL;DR: In this article, the authors derived the spin-orbit terms in the multipole moments of the compact binary system up to the same order within the multipolar post-Newtonian wave generation formalism.
Abstract: We compute the next-to-next-to-leading order spin–orbit contributions in the total energy flux emitted in gravitational waves by compact binary systems. Such contributions correspond to the post-Newtonian order 3.5PN for maximally spinning compact objects. Continuing our recent work on the next-to-next-to-leading spin–orbit terms at the 3.5PN order in the equations of motion, we obtain the spin–orbit terms in the multipole moments of the compact binary system up to the same order within the multipolar post-Newtonian wave generation formalism. Our calculation of the multipole moments is valid for general orbits and in an arbitrary frame, the moments are then reduced to the center-of-mass frame and the resulting energy flux is specialized to quasi-circular orbits. The test-mass limit of our final result for the flux agrees with the already known Kerr black hole perturbation limit. Furthermore, the various multipole moments of the compact binary reduce in the one-body case to those of a single-boosted Kerr black hole. We briefly discuss the implications of our result for the gravitational wave flux in terms of the binary’s phase evolution, and address its importance for the future detection and parameter estimation of signals in gravitational wave detectors.

Journal ArticleDOI
TL;DR: In this article, the minimal geometric deformation approach (MGD) was used to generate a new physically acceptable interior solution to Einstein's field equations for a spherically symmetric compact distribution, which is used to elucidate the role of exterior Weyl stresses from bulk gravitons on compact stellar distributions.
Abstract: In the context of the Randall-Sundrum braneworld, the minimal geometric deformation approach (MGD) is used to generate a new physically acceptable interior solution to Einstein’s field equations for a spherically symmetric compact distribution. This new solution is used to elucidate the role of exterior Weyl stresses from bulk gravitons on compact stellar distributions. We found strong evidences showing that the exterior dark radiation U + always increases both the pressure and the compactness of stellar structures, and that the exterior “dark pressure” P + always reduces them.

Journal ArticleDOI
TL;DR: The first stage of the NRAR project focused on producing an initial set of numerical waveforms from binary black holes with moderate mass ratios and spins, as well as one non-spinning binary configuration which has a mass ratio of 10 as mentioned in this paper.
Abstract: The Numerical–Relativity–Analytical–Relativity (NRAR) collaboration is a joint effort between members of the numerical relativity, analytical relativity and gravitational-wave data analysis communities. The goal of the NRAR collaboration is to produce numerical-relativity simulations of compact binaries and use them to develop accurate analytical templates for the LIGO/Virgo Collaboration to use in detecting gravitational-wave signals and extracting astrophysical information from them. We describe the results of the first stage of the NRAR project, which focused on producing an initial set of numerical waveforms from binary black holes with moderate mass ratios and spins, as well as one non-spinning binary configuration which has a mass ratio of 10. All of the numerical waveforms are analysed in a uniform and consistent manner, with numerical errors evaluated using an analysis code created by members of the NRAR collaboration. We compare previously-calibrated, non-precessing analytical waveforms, notably the effective-one-body (EOB) and phenomenological template families, to the newly-produced numerical waveforms. We find that when the binary's total mass is ~100–200M⊙, current EOB and phenomenological models of spinning, non-precessing binary waveforms have overlaps above 99% (for advanced LIGO) with all of the non-precessing-binary numerical waveforms with mass ratios ≤4, when maximizing over binary parameters. This implies that the loss of event rate due to modelling error is below 3%. Moreover, the non-spinning EOB waveforms previously calibrated to five non-spinning waveforms with mass ratio smaller than 6 have overlaps above 99.7% with the numerical waveform with a mass ratio of 10, without even maximizing on the binary parameters.

Journal ArticleDOI
TL;DR: In this paper, Singh et al. studied the evolution of anisotropies in a model where an ekpyrotic phase of contraction is followed by domination of a Galileon-type Lagrangian which generates a non-singular bounce.
Abstract: Following recent claims relative to the question of large anisotropy production in regular bouncing scenarios, we study the evolution of such anisotropies in a model where an ekpyrotic phase of contraction is followed by domination of a Galileon-type Lagrangian which generates a non-singular bounce. We show that the anisotropies decrease during the phase of ekpyrotic contraction (as expected) and that they can be constrained to remain small during the non-singular bounce phase (a non-trivial result). Specifically, we derive the e-folding number of the phase of ekpyrotic contraction which leads to a present-day anisotropy in agreement with current observational bounds. Communicated by P Singh

Journal ArticleDOI
TL;DR: In this paper, the effects of cosmological perturbations and derivatives on the Nambu-Goldstone modes are investigated. But the authors focus on a special case of the effects, namely the effect of gravity and dark energy.
Abstract: The effective field theory of cosmological perturbations stems from considering a cosmological background solution as a state displaying spontaneous breaking of time translations and (adiabatic) perturbations as the related Nambu-Goldstone modes. With this insight, one can systematically develop a theory for the cosmological perturbations during inflation and, with minor modifications, also describe in full generality the gravitational interactions of dark energy, which are relevant for late-time cosmology. The formalism displays a unique set of Lagrangian operators containing an increasing number of cosmological perturbations and derivatives. We give an introductory description of the unitary gauge formalism for theories with broken gauge symmetry---that allows to write down the most general Lagrangian---and of the Stueckelberg "trick"---that allows to recover gauge invariance and to make the scalar field explicit. We show how to apply this formalism to gravity and cosmology and we reproduce the detailed analysis of the action in the ADM variables. We also review some basic applications to inflation and dark energy.

Journal ArticleDOI
TL;DR: In this article, the authors review the current status of spin measurements in supermassive black holes (SMBH) and discuss the recent discovery of relativistic x-ray reverberation which can be used to 'echo map' the innermost regions of the accretion disc.
Abstract: Black hole spin is a quantity of great interest to both physicists and astrophysicists. We review the current status of spin measurements in supermassive black holes (SMBH). To date, every robust SMBH spin measurement uses x-ray reflection spectroscopy, so we focus almost exclusively on this technique as applied to moderately-luminous active galactic nuclei (AGN). After describing the foundations and uncertainties of the method, we summarize the current status of the field. At the time of writing, observations by XMM-Newton, Suzaku and NuSTAR have given robust spin constraints on 22 SMBHs. We find a significant number of rapidly rotating SMBHs (with dimensionless spin parameters a > 0.9) although, especially at the higher masses (M > 4 × 107M⊙), there are also some SMBHs with intermediate spin parameters. This may be giving us our first hint at a mass-dependent spin distribution which would, in turn, provide interesting constraints on models for SMBH growth. We also discuss the recent discovery of relativistic x-ray reverberation which we can use to 'echo map' the innermost regions of the accretion disc. The ultimate development of these reverberation techniques, when applied to data from future high-throughput x-ray observatories such as LOFT, ATHENA+, and AXSIO, will permit the measurement of black hole spin by a characterization of strong-field Shapiro delays. We conclude with a brief discussion of other electromagnetic methods that have been attempted or are being developed to constrain SMBH spin.

Journal ArticleDOI
TL;DR: In this article, the authors extend their previous work devoted to the computation of the next-next-to-leading order spin-orbit correction (corresponding to 3.5PN order) in the equations of motion of spinning compact binaries by deriving the corresponding spinorbit terms in the evolution equations for the spins, the conserved integrals of the motion and the metric regularized at the location of the particles (obtaining also the metric all over the near zone but with some lower precision).
Abstract: We extend our previous work devoted to the computation of the next-to-next-to-leading order spin–orbit correction (corresponding to 3.5PN order) in the equations of motion of spinning compact binaries by (i) deriving the corresponding spin–orbit terms in the evolution equations for the spins, the conserved integrals of the motion and the metric regularized at the location of the particles (obtaining also the metric all over the near zone but with some lower precision); (ii) performing the orbital reduction of the precession equations, near-zone metric and conserved integrals to the center-of-mass frame and then further assuming quasi-circular orbits (neglecting gravitational radiation reaction). The results are systematically expressed in terms of the spin variables with a conserved Euclidean norm instead of the original antisymmetric spin tensors of the pole–dipole formalism. This work paves the way to the future computation of the next-to-next-to-leading order spin–orbit terms in the gravitational-wave phasing of spinning compact binaries.

Journal ArticleDOI
TL;DR: A survey of the known cosmological and black hole solutions in ghost-free bigravity and massive gravity theories can be found in this paper, where they can be divided into three classes: proportional, non-bidiagonal and time-dependent solutions.
Abstract: We present a survey of the known cosmological and black hole solutions in ghost-free bigravity and massive gravity theories. These can be divided into three classes. First, there are solutions with proportional metrics, which are the same as in General Relativity with a cosmological term, which can be positive, negative or zero. Secondly, for spherically symmetric systems, there are solutions with non-bidiagonal metrics. The g-metric fulfils Einstein equations with a positive cosmological term and a matter source, while the f-metric is anti-de Sitter. The third class contains solutions with bidiagonal metrics, and these can be quite complex. The time-dependent solutions describe homogeneous (isotropic or anisotropic) cosmologies which show a late-time self-acceleration or other types of behavior. The static solutions describe black holes with a massive graviton hair, and also globally regular lumps of energy. None of these are asymptotically flat. Including a matter source gives rise to asymptotically flat solutions which exhibit the Vainshtein mechanism of recovery of General Relativity in a finite region.

Journal ArticleDOI
TL;DR: In this article, the main results that have been obtained in quantum cosmology from the perspective of the de Broglie?Bohm quantum theory are reviewed and compared with other approaches, and the physical reasons for some discrepancies that occur.
Abstract: We review the main results that have been obtained in quantum cosmology from the perspective of the de Broglie?Bohm quantum theory. As it is a dynamical theory of assumed objectively real trajectories in the configuration space of the physical system under investigation, this quantum theory is not essentially probabilistic and dispenses the collapse postulate, turning it suitable to be applied to cosmology. In the framework of minisuperspace models, we show how quantum cosmological effects in the de?Broglie-Bohm approach can avoid the initial singularity, and isotropize the Universe. We then extend minisuperspace in order to include linear cosmological perturbations. We present the main equations which govern the dynamics of quantum cosmological perturbations evolving in non-singular quantum cosmological backgrounds, and calculate some of their observational consequences. These results are not known how to be obtained in other approaches to quantum theory. In the general case of full superspace, we enumerate the possible structures of quantum space and time that emerge from the de Broglie?Bohm picture. Finally, we compare some of the results coming from the de Broglie?Bohm theory with other approaches, and discuss the physical reasons for some discrepancies that occur.

Journal ArticleDOI
TL;DR: In this article, a first-principle derivation of a master equation for the evolution of a quantum matter field in a linearly perturbed Minkowski spacetime, based solely on quantum field theory and general relativity, was given.
Abstract: We give a first principles derivation of a master equation for the evolution of a quantum matter field in a linearly perturbed Minkowski spacetime, based solely on quantum field theory and general relativity We make no additional assumptions nor introduce extra ingredients, as is often done in alternative quantum theories When the quantum matter field is projected to a one-particle state, the master equation for a non-relativistic quantum particle in a weak gravitational field predicts decoherence in the energy basis, in contrast to most existing theories of gravitational decoherence We point out the gauge nature of time and space reparameterizations in matter–gravity couplings, and warn that ‘intrinsic’ decoherence or alternative quantum theories invoking stochastic dynamics arising from temporal or spatial fluctuations violate this fundamental symmetry of classical general relativity Interestingly we find that the decoherence rate depends on extra parameters other than the Planck scale, an important feature of gravitational decoherence This is similar to the dependence of the decoherence rate of a quantum Brownian particle to the temperature and spectral density of the environment it interacts with The corresponding features when gravity acts as an environment in decohering quantum objects are what we call the ‘textures’ of spacetime We point out the marked difference between the case when gravity is represented as a background spacetime versus the case when gravity acts like a thermodynamic bath to quantum particles This points to the possibility of using gravitational decoherence measurements to discern whether gravity is intrinsically elemental or emergent

Journal ArticleDOI
TL;DR: In this paper, a detailed dynamical analysis of various cosmological scenarios in extended (varying-mass) nonlinear massive gravity is performed, which allows for a huge variety of solutions that can attract the universe at late times.
Abstract: We perform a detailed dynamical analysis of various cosmological scenarios in extended (varying-mass) nonlinear massive gravity. Due to the enhanced freedom in choosing the involved free functions, this cosmological paradigm allows for a huge variety of solutions that can attract the universe at late times, comparing to scalar-field cosmology or usual nonlinear massive gravity. Amongst others, it accepts quintessence, phantom, or cosmological-constant-like late-time solutions, which moreover can alleviate the coincidence problem. These features seem to be general and non-sensitive to the imposed ansantzes and model parameters, and thus extended nonlinear massive gravity can be a good candidate for the description of nature.