The open-access journal Living Reviews in Relativity has recently published two new major updates of review articles:

“The Kerr/CFT correspondence and its extensions” by Geoffrey Compere (http://dx.doi.org/10.1007/s41114-017-0003-2) and “Interferometer techniques for gravitational-wave detection” by Charlotte Bond, Daniel Brown, Andreas Freise and Kenneth A. Strain (http://dx.doi.org/10.1007/s41114-016-0002-8).

Due to a technical error, the latter was published with a wrong article citation ID, which will be corrected as soon as possible. We would also like to apologize to the authors for the tremendous delays caused by workflow adjustments after the journal transfer to Springer.

The open-access journal Living Reviews in Relativity has published a new review article on “Extraction of gravitational waves in numerical relativity” by Nigel T. Bishop and Luciano Rezzolla on 4 October 2016 (metadata correction 10 November 2016):

Bishop, N.T. and Rezzolla, L.,
“Extraction of gravitational waves in numerical relativity”,
Living Rev Relativ (2016) 19: 2.
http://doi.org/10.1007/s41114-016-0001-9

ABSTRACT:
A numerical-relativity calculation yields in general a solution of the Einstein equations including also a radiative part, which is in practice computed in a region of finite extent. Since gravitational radiation is properly defined only at null infinity and in an appropriate coordinate system, the accurate estimation of the emitted gravitational waves represents an old and non-trivial problem in numerical relativity. A number of methods have been developed over the years to “extract” the radiative part of the solution from a numerical simulation and these include: quadrupole formulas, gauge-invariant metric perturbations, Weyl scalars, and characteristic extraction. We review and discuss each method, in terms of both its theoretical background as well as its implementation. Finally, we provide a brief comparison of the various methods in terms of their inherent advantages and disadvantages.

Living Reviews in Relativity has published a new review article on “Terrestrial Gravity Fluctuations” by Jan Harms on 2 December 2015.

Living Reviews in Computational Astrophysics has published a new review article on “Grid-based Methods in Relativistic Hydrodynamics and Magnetohydrodynamics” by Jose Maria Marti and Ewald Mueller on 22 December 2015.

Please find the abstracts and further details below.

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PUB.NO. lrca-2015-3
Marti, Jose Maria and Mueller, Ewald
“Grid-based Methods in Relativistic Hydrodynamics and Magnetohydrodynamics”

ACCEPTED: 2015-12-01
PUBLISHED: 2015-12-22

FULL ARTICLE AT:
http://www.livingreviews.org/lrca-2015-3

ABSTRACT:
An overview of grid-based numerical methods used in relativistic hydrodynamics (RHD) and magnetohydrodynamics (RMHD) is presented. Special emphasis is put on a comprehensive review of the application of high-resolution shock-capturing methods. Results of a set of demanding test bench simulations obtained with different numerical methods are compared in an attempt to assess the present capabilities and limits of the various numerical strategies. Applications to three astrophysical phenomena are briefly discussed to motivate the need for and to demonstrate the success of RHD and RMHD simulations in their understanding. The review further provides FORTRAN programs to compute the exact solution of the Riemann problem in RMHD, and to simulate 1D RMHD flows in Cartesian coordinates.

UPCOMING ARTICLES AT:
http://computastrophys.livingreviews.org/Articles/upcoming.html

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PUB.NO. lrr-2015-3
Harms, Jan
“Terrestrial Gravity Fluctuations”

ACCEPTED: 2015-11-16
PUBLISHED: 2015-12-02

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2015-3

ABSTRACT:
Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10^-23 Hz^-1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of terrestrial gravity fluctuations will have great impact on the future development of GW detectors and high-precision gravimetry in general, and many open questions need to be answered still as emphasized in this article.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity had been recently acquired by Springer and has now resumed publication with two new review articles: “Exploring New Physics Frontiers Through Numerical Relativity” by Vitor Cardoso et al. and “The Hubble Constant” (major update) by Neal Jackson.

Please find the abstracts and further details below.

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PUB.NO. lrr-2015-1
Vitor Cardoso, Leonardo Gualtieri, Carlos A. R. Herdeiro and Ulrich Sperhake,
“Exploring New Physics Frontiers Through Numerical Relativity”

PUBLISHED: 2015-09-21

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2015-1

ABSTRACT:
The demand to obtain answers to highly complex problems within strong-field gravity has been met with significant progress in the numerical solution of Einstein’s equations – along with some spectacular results – in various setups. We review techniques for solving Einstein’s equations in generic spacetimes, focusing on fully nonlinear evolutions but also on how to benchmark those results with perturbative approaches. The results address problems in high-energy physics, holography, mathematical physics, fundamental physics, astrophysics and cosmology.

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PUB.NO. lrr-2015-2
Neal Jackson
“The Hubble Constant” (major update)

PUBLISHED: 2015-09-24

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2015-2

ABSTRACT:
I review the current state of determinations of the Hubble constant, which gives the lengthscale of the Universe by relating the expansion velocity of objects to their distance. There are two broad categories of measurements. The first uses individual astrophysical objects which have some property that allows their intrinsic luminosity or size to be determined, or allows the determination of their distance by geometric means. The second category comprises the use of all-sky cosmic microwave background, or correlations between large samples of galaxies, to determine information about the geometry of the Universe and hence the Hubble constant, typically in a combination with other cosmological parameters. Many, but not all, object-based measurements give H_0 values of around 72 – 74 km s^–1 Mpc^–1, with typical errors of 2 – 3 km s^–1 Mpc^–1. This is in mild discrepancy with CMB-based measurements, in particular those from the Planck satellite, which give values of 67 – 68 km s^–1 Mpc^–1 and typical errors of 1 – 2 km s^–1 Mpc^–1. The size of the remaining systematics indicate that accuracy rather than precision is the remaining problem in a good determination of the Hubble constant. Whether a discrepancy exists, and whether new physics is needed to resolve it, depends on details of the systematics of the object-based methods, and also on the assumptions about other cosmological parameters and which datasets are combined in the case of the all-sky methods.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity recently published two new articles: a major update of the review on “Time-Delay Interferometry” by Massimo Tinto and Sanjeev V. Dhurandhar and a new article on “Massive Gravity” by Claudia de Rham.

Please find the abstracts and further details below.

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PUB.NO. lrr-2014-7
de Rham, Claudia
“Massive Gravity”

ACCEPTED: 2014-07-18
PUBLISHED: 2014-08-25

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2014-7

ABSTRACT:
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali-Gabadadze-Porrati model (DGP), cascading gravity and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware-Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alternative and related models of massive gravity such as new massive gravity, Lorentz-violating massive gravity and non-local massive gravity.

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PUB.NO. lrr-2014-6
Tinto, Massimo and Dhurandhar, Sanjeev V.
“Time-Delay Interferometry”

ACCEPTED: 2014-07-28
PUBLISHED: 2014-08-05

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2014-6

ABSTRACT:
Equal-arm detectors of gravitational radiation allow phase measurements many orders of magnitude below the intrinsic phase stability of the laser injecting light into their arms. This is because the noise in the laser light is common to both arms, experiencing exactly the same delay, and thus cancels when it is differenced at the photo detector. In this situation, much lower level secondary noises then set the overall performance. If, however, the two arms have different lengths (as will necessarily be the case with space-borne interferometers), the laser noise experiences different delays in the two arms and will hence not directly cancel at the detector. In order to solve this problem, a technique involving heterodyne interferometry with unequal arm lengths and independent phase-difference readouts has been proposed. It relies on properly time-shifting and linearly combining independent Doppler measurements, and for this reason it has been called time-delay interferometry (TDI). This article provides an overview of the theory, mathematical foundations, and experimental aspects associated with the implementation of TDI. Although emphasis on the application of TDI to the Laser Interferometer Space Antenna (LISA) mission appears throughout this article, TDI can be incorporated into the design of any future space-based mission aiming to search for gravitational waves via interferometric measurements. We have purposely left out all theoretical aspects that data analysts will need to account for when analyzing the TDI data combinations.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity has published a new review article on “On the History of Unified Field Theories. Part II (ca. 1930 – ca. 1965)” by Hubert F. M. Goenner on 23 June 2014.

Please find the abstract and further details below.

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PUB.NO. lrr-2014-5
Goenner, Hubert F. M.
“On the History of Unified Field Theories. Part II (ca. 1930 – ca. 1965)”

ACCEPTED: 2014-05-13
PUBLISHED: 2014-06-23

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2014-5

ABSTRACT:
The present review intends to provide an overall picture of the research concerning classical unified field theory, worldwide, in the decades between the mid-1930 and mid-1960. Main themes are the conceptual and methodical development of the field, the interaction among the scientists working in it, their opinions and interpretations. Next to the most prominent players, A. Einstein and E. Schrodinger, V. Hlavaty and the French groups around A. Lichnerowicz, M.-A. Tonnelat, and Y. Thiry are presented. It is shown that they have given contributions of comparable importance. The review also includes a few sections on the fringes of the central topic like Born-Infeld electromagnetic theory or scalar-tensor theory. Some comments on the structure and organization of research-groups are also made.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published an update of the review “The Confrontation between General Relativity and Experiment” by Clifford M. Will on 11 June 2014.

Please find the abstract and further details below.

This new edition of one of our most read reviews also marks a new milestone the journal’s history: as of this day, Living Reviews has published 130 articles on 90 topics!

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PUB.NO. lrr-2014-4
Will, Clifford M.
“The Confrontation between General Relativity and Experiment”

ACCEPTED: 2014-06-06
PUBLISHED: 2014-06-11

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2014-4

ABSTRACT:
The status of experimental tests of general relativity and of theoretical frameworks for analyzing them are reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

UPDATE NOTE:
Major revision, updated and expanded. Added new Section 2.3.3 on the Pioneer anomaly; split former Section 3 into new 3 and 4, and extended Section 3.3 on competing theories of gravity; added new Sections 5.3 and 5.4 on compact binary systems; added a new Section 8 on astrophysical and cosmological tests. The number of references increased from 299 to 454. Added two figures (8, 9) and updated Figures 1, 3, 5, and 7.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity has published a major update of the review “The Evolution of Compact Binary Star Systems” by Konstantin A. Postnov and Lev R. Yungelson on 5 May 2014.

Please find the abstract and further details below.

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PUB.NO. lrr-2014-3
Postnov, Konstantin A. and Yungelson, Lev R.
“The Evolution of Compact Binary Star Systems”

ACCEPTED: 2014-03-17
PUBLISHED: 2014-05-05

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2014-3

ABSTRACT:
We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Mergings of compact-star binaries are expected to be the most important sources for forthcoming gravitational-wave (GW) astronomy. In the first part of the review, we discuss observational manifestations of close binaries with NS and/or BH components and their merger rate, crucial points in the formation and evolution of compact stars in binary systems, including the treatment of the natal kicks, which NSs and BHs acquire during the core collapse of massive stars and the common envelope phase of binary evolution, which are most relevant to the merging rates of NS-NS, NS-BH and BH-BH binaries. The second part of the review is devoted mainly to the formation and evolution of binary WDs and their observational manifestations, including their role as progenitors of cosmologically-important thermonuclear SN Ia. We also consider AM CVn-stars, which are thought to be the best verification binary GW sources for future low-frequency GW space interferometers.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity recently published two new articles: a major update of the review on “Gravitational Radiation from Post-Newtonian Sources and Inspiralling Compact Binaries” by Luc Blanchet and a new article on “The Hole Argument and Some Physical and Philosophical Implications” by John Stachel.

Please find the abstracts and further details below.

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PUB.NO. lrr-2014-2
Blanchet, Luc
“Gravitational Radiation from Post-Newtonian Sources and Inspiralling Compact Binaries”

ACCEPTED: 2014-01-27
PUBLISHED: 2014-02-14

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2014-2

ABSTRACT:
To be observed and analyzed by the network of gravitational wave detectors on ground (LIGO, VIRGO, etc.) and by the future detectors in space (eLISA, etc.), inspiralling compact binaries — binary star systems composed of neutron stars and/or black holes in their late stage of evolution — require high-accuracy templates predicted by general relativity theory. The gravitational waves emitted by these very relativistic systems can be accurately modelled using a high-order post-Newtonian gravitational wave generation formalism. In this article, we present the current state of the art on post-Newtonian methods as applied to the dynamics and gravitational radiation of general matter sources (including the radiation reaction back onto the source) and inspiralling compact binaries. We describe the post-Newtonian equations of motion of compact binaries and the associated Lagrangian and Hamiltonian formalisms, paying attention to the self-field regularizations at work in the calculations. Several notions of innermost circular orbits are discussed. We estimate the accuracy of the post-Newtonian approximation and make a comparison with numerical computations of the gravitational self-force for compact binaries in the small mass ratio limit. The gravitational waveform and energy flux are obtained to high post-Newtonian order and the binary’s orbital phase evolution is deduced from an energy balance argument. Some landmark results are given in the case of eccentric compact binaries — moving on quasi-elliptical orbits with non-negligible eccentricity. The spins of the two black holes play an important role in the definition of the gravitational wave templates. We investigate their imprint on the equations of motion and gravitational wave phasing up to high post-Newtonian order (restricting to spin-orbit effects which are linear in spins), and analyze the post-Newtonian spin precession equations as well as the induced precession of the orbital plane.

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PUB.NO. lrr-2014-1
Stachel, John
“The Hole Argument and Some Physical and Philosophical Implications”

ACCEPTED: 2013-11-17
PUBLISHED: 2014-02-06

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2014-1

ABSTRACT:
This is a historical-critical study of the hole argument, concentrating on the interface between historical, philosophical and physical issues. Although it includes a review of its history, its primary aim is a discussion of the contemporary implications of the hole argument for physical theories based on dynamical, background-independent space-time structures.

The historical review includes Einstein’s formulations of the hole argument, Kretschmann’s critique, as well as Hilbert’s reformulation and Darmois’ formulation of the general-relativistic Cauchy problem. The 1970s saw a revival of interest in the hole argument, growing out of attempts to answer the question: Why did three years elapse between Einstein’s adoption of the metric tensor to represent the gravitational field and his adoption of the Einstein field equations?

The main part presents some modern mathematical versions of the hole argument, including both coordinate-dependent and coordinate-independent definitions of covariance and general covariance; and the fiber bundle formulation of both natural and gauge natural theories. By abstraction from continuity and differentiability, these formulations can be extended from differentiable manifolds to any set; and the concepts of permutability and general permutability applied to theories based on relations between the elements of a set, such as elementary particle theories.

We are closing with an overview of current discussions of philosophical and physical implications of the hole argument.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity has published a new review article on “Gravitational-Wave Tests of General Relativity with Ground-Based Detectors and Pulsar-Timing Arrays” by Nicolas Yunes and Xavier Siemens on 6 November 2013.

Please find the abstract and further details below.

This publication also introduces a redesigned HTML article layout, which allows better indexing by search engines and improves usability (easy linking to sections and figures, replacement for popups):

http://relativity.livingreviews.org/Articles/lrr-2013-9/fulltext.html

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PUB.NO. lrr-2013-9
Yunes, Nicolas and Siemens, Xavier
“Gravitational-Wave Tests of General Relativity with Ground-Based Detectors and Pulsar-Timing Arrays”

ACCEPTED: 2013-10-08
PUBLISHED: 2013-11-06

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-9

ABSTRACT:
This review is focused on tests of Einstein’s theory of general relativity with gravitational waves that are detectable by ground-based interferometers and pulsar-timing experiments. Einstein’s theory has been greatly constrained in the quasi-linear, quasi-stationary regime, where gravity is weak and velocities are small. Gravitational waves will allow us to probe a complimentary, yet previously unexplored regime: the non-linear and dynamical strong-field regime. Such a regime is, for example, applicable to compact binaries coalescing, where characteristic velocities can reach fifty percent the speed of light and gravitational fields are large and dynamical. This review begins with the theoretical basis and the predicted gravitational-wave observables of modified gravity theories. The review continues with a brief description of the detectors, including both gravitational-wave interferometers and pulsar-timing arrays, leading to a discussion of the data analysis formalism that is applicable for such tests. The review ends with a discussion of gravitational-wave tests for compact binary systems.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity has published three new review articles:

“Cosmology and Fundamental Physics with the Euclid Satellite” by Luca Amendola et al. (Euclid Theory Working Group),

“Testing General Relativity with Low-Frequency, Space-Based Gravitational-Wave Detectors” by Jonathan R. Gair et al.,

“Classification of Near-Horizon Geometries of Extremal Black Holes” by Hari K. Kunduri and James Lucietti.

Please find the abstract and further details below.

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PUB.NO. lrr-2013-6
Luca Amendola et al. (Euclid Theory Working Group)
“Cosmology and Fundamental Physics with the Euclid Satellite”

ACCEPTED: 2013-06-13
PUBLISHED: 2013-09-02

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-6

ABSTRACT:
Euclid is a European Space Agency medium-class mission selected for launch in 2019 within the Cosmic Vision 2015-2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the Universe. Euclid will explore the expansion history of the Universe and the evolution of cosmic structures by measuring shapes and redshifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid’s Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

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PUB.NO. lrr-2013-7
Jonathan R. Gair, Michele Vallisneri, Shane L. Larson and John G. Baker
“Testing General Relativity with Low-Frequency, Space-Based Gravitational-Wave Detectors”

ACCEPTED: 2013-08-19
PUBLISHED: 2013-09-12

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-7

ABSTRACT:
We review the tests of general relativity that will become possible with space-based gravitational-wave detectors operating in the $sim 10^5 – 1$ Hz low-frequency band. The fundamental aspects of gravitation that can be tested include the presence of additional gravitational fields other than the metric; the number and tensorial nature of gravitational-wave polarization states; the velocity of propagation of gravitational waves; the binding energy and gravitational-wave radiation of binaries, and therefore the time evolution of binary inspirals; the strength and shape of the waves emitted from binary mergers and ringdowns; the true nature of astrophysical black holes; and much more. The strength of this science alone calls for the swift implementation of a space-based detector; the remarkable richness of astrophysics, astronomy, and cosmology in the low-frequency gravitational-wave band make the case even stronger.

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PUB.NO. lrr-2013-8
Kunduri, Hari K. and Lucietti, James
“Classification of Near-Horizon Geometries of Extremal Black Holes”

ACCEPTED: 2013-09-11
PUBLISHED: 2013-09-25

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-8

ABSTRACT:
Any spacetime containing a degenerate Killing horizon, such as an extremal black hole, possesses a well-defined notion of a near-horizon geometry. We review such near-horizon geometry solutions in a variety of dimensions and theories in a unified manner. We discuss various general results including horizon topology and near-horizon symmetry enhancement. We also discuss the status of the classification of near-horizon geometries in theories ranging from vacuum gravity to Einstein–Maxwell theory and supergravity theories. Finally, we discuss applications to the classification of extremal black holes and various related topics. Several new results are presented and open problems are highlighted throughout.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a new review article on “Quantum-Spacetime Phenomenology” by Giovanni Amelino-Camelia on 12 June 2013.

Please find the abstract and further details below.

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PUB.NO. lrr-2013-5
Amelino-Camelia, Giovanni
“Quantum-Spacetime Phenomenology”

ACCEPTED: 2013-05-18
PUBLISHED: 2013-06-12

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-5

ABSTRACT:
I review the current status of phenomenological programs inspired by quantum-spacetime research. I stress in particular the significance of results establishing that certain data analyses provide sensitivity to effects introduced genuinely at the Planck scale. My main focus is on phenomenological programs that managed to affect the directions taken by studies of quantum-spacetime theories.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a major update of the review “Relativistic Binaries in Globular Clusters” by Matthew J. Benacquista and Jonathan M.B. Downing on 4 March 2013.

Please find the abstract and further details below.

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PUB.NO. lrr-2013-4
Benacquista, Matthew J. and Downing, Jonathan M.B.
“Relativistic Binaries in Globular Clusters”

ACCEPTED: 2012-11-29
PUBLISHED: 2013-03-04

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-4

ABSTRACT:
Galactic globular clusters are old, dense star systems typically containing 10^4 – 10^6 stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution that leads to relativistic binaries, and current and possible future observational evidence for this population. Our discussion of globular cluster evolution will focus on the processes that boost the production of tight binary systems and the subsequent interaction of these binaries that can alter the properties of both bodies and can lead to exotic objects. Direct N-body integrations and Fokker–Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity has published two new review articles on Quantum Gravity:

“The Spin-Foam Approach to Quantum Gravity” by Alejandro Perez and “Minimal Length Scale Scenarios for Quantum Gravity” by Sabine Hossenfelder.

Please find the abstract and further details below.

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PUB.NO. lrr-2013-3
Perez, Alejandro
“The Spin-Foam Approach to Quantum Gravity”

ACCEPTED: 2012-06-11
PUBLISHED: 2012-02-14

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-3

ABSTRACT:
This article reviews the present status of the spin-foam approach to the quantization of gravity. Special attention is payed to the pedagogical presentation of the recently-introduced new models for four-dimensional quantum gravity. The models are motivated by a suitable implementation of the path integral quantization of the Plebanski formulation of gravity on a simplicial regularization. The article also includes a self contained treatment of 2+1 gravity. The simple nature of the latter provides the basis and a perspective for the analysis of both conceptual and technical issues that remain open in four dimensions.

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PUB.NO. lrr-2013-2
Hossenfelder, Sabine
“Minimal Length Scale Scenarios for Quantum Gravity”

ACCEPTED: 2012-10-11
PUBLISHED: 2013-01-29

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-2

ABSTRACT:
We review the question whether the fundamental laws of nature limit our ability to probe arbitrarily short distances. First, we examine what insights can be gained from thought experiments for probes of shortest distances, and summarize what can be learned from different approaches to a theory of quantum gravity. Then we discuss some models that have been developed to implement a minimal length scale into quantum mechanics and quantum field theory. These models have entered the literature under the names of generalized uncertainty principle or modified dispersion relation, and have allowed to study the effects of a minimal length scale in quantum mechanics, quantum electrodynamics, thermodynamics, black hole physics and cosmology. Finally, we touch upon the question if there are ways to circumvent the manifestation of a minimal length scale in short-distance physics.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a new review article on “Foundations of Black Hole Accretion Disk Theory” by Marek A. Abramowicz and P. Chris Fragile on 14 January 2013.

Please find the abstract and further details below.

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PUB.NO. lrr-2013-1
Abramowicz, Marek A. and Fragile, P. Chris
“Foundations of Black Hole Accretion Disk Theory”

ACCEPTED: 2012-11-15
PUBLISHED: 2013-01-14

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2013-1

ABSTRACT:
This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura–Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a new review article on “The Kerr/CFT Correspondence and its Extensions” by Geoffrey Compère on 22 October 2012.

Please find the abstract and further details below.

NEW: Follow us on Twitter http://twitter.com/livrev_lrr

PUB.NO. lrr-2012-11
Compère, Geoffrey
“The Kerr/CFT Correspondence and its Extensions”

ACCEPTED: 2012-06-13
PUBLISHED: 2012-10-22

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-11

ABSTRACT:
We present a first-principles derivation of the main results of the Kerr/CFT correspondence and its extensions using only tools from gravity and quantum field theory, filling a few gaps in the literature when necessary. Firstly, we review properties of extremal black holes that imply, according to semi-classical quantization rules, that their near-horizon quantum states form a centrally-extended representation of the one-dimensional conformal group. This motivates the conjecture that the extremal Kerr and Reissner–Nordstr”om black holes are dual to the chiral limit of a two-dimensional conformal field theory. We also motivate the existence of a $SL(2,mathbb Z)$ family of two-dimensional conformal field theories which describe in their chiral limit the extremal Kerr–Newman black hole. We present generalizations in anti-de Sitter spacetime and discuss other matter coupling and higher derivative corrections. Secondly, we show how a near-chiral limit of these CFTs reproduces the dynamics of near-superradiant probes around near-extremal black holes in the semi-classical limit. Thirdly, we review how the hidden conformal symmetries of asymptotically flat black holes away from extremality combined with their properties at extremality allow for a microscopic accounting of the entropy of non-extremal asymptotically flat rotating or charged black holes. We conclude with a list of open problems.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a new review article on “Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions” by Benoît Famaey and Stacy S. McGaugh on 7 September 2012.

Please find the abstract and further details below.

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PUB.NO. lrr-2012-10
Famaey, Benoît and McGaugh, Stacy S.
“Modified Newtonian Dynamics (MOND): Observational Phenomenology and
Relativistic Extensions”

ACCEPTED: 2012-04-30
PUBLISHED: 2012-09-07

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-10

(incl. 518 references and 48 figures)

ABSTRACT:
A wealth of astronomical data indicate the presence of mass discrepancies in the Universe. The motions observed in a variety of classes of extragalactic systems exceed what can be explained by the mass visible in stars and gas. Either (i) there is a vast amount of unseen mass in some novel form — dark matter — or (ii) the data indicate a breakdown of our understanding of dynamics on the relevant scales, or (iii) both. Here, we first review a few outstanding challenges for the dark matter interpretation of mass discrepancies in galaxies, purely based on observations and independently of any alternative theoretical framework. We then show that many of these puzzling observations are predicted by one single relation — Milgrom’s law — involving an acceleration constant $a_0$ (or a characteristic surface density $Sigma_dagger = a_0/G$) on the order of the square-root of the cosmological constant in natural units. This relation can at present most easily be interpreted as the effect of a single universal force law resulting from a modification of Newtonian dynamics (MOND) on galactic scales. We exhaustively review the current observational successes and problems of this alternative paradigm at all astrophysical scales, and summarize the various theoretical attempts (TeVeS, GEA, BIMOND, and others) made to effectively embed this modification of Newtonian dynamics within a relativistic theory of gravity.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a new review article on “Continuum and Discrete Initial-Boundary-Value Problems and Einstein’s Field Equations” by Olivier Sarbach and Manuel Tiglio on 27 August 2012.

Please find the abstract and further details below.

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PUB.NO. lrr-2012-9
Sarbach, Olivier and Tiglio, Manuel
“Continuum and Discrete Initial-Boundary-Value Problems and Einstein’s Field Equations”

ACCEPTED: 2012-05-02
PUBLISHED: 2012-08-27

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-9

(incl. 457 references and 17 figures)

ABSTRACT:
Many evolution problems in physics are described by partial differential equations on an infinite domain; therefore, one is interested in the solutions to such problems for a given initial dataset. A prominent example is the binary black-hole problem within Einstein’s theory of gravitation, in which one computes the gravitational radiation emitted from the inspiral of the two black holes, merger and ringdown. Powerful mathematical tools can be used to establish qualitative statements about the solutions, such as their existence, uniqueness, continuous dependence on the initial data, or their asymptotic behavior over large time scales. However, one is often interested in computing the solution itself, and unless the partial differential equation is very simple, or the initial data possesses a high degree of symmetry, this computation requires approximation by numerical discretization. When solving such discrete problems on a machine, one is faced with a finite limit to computational resources, which leads to the replacement of the infinite continuum domain with a finite computer grid. This, in turn, leads to a discrete initial-boundary value problem. The hope is to recover, with high accuracy, the exact solution in the limit where the grid spacing converges to zero with the boundary being pushed to infinity.

The goal of this article is to review some of the theory necessary to understand the continuum and discrete initial boundary-value problems arising from hyperbolic partial differential equations and to discuss its applications to numerical relativity; in particular, we present well-posed initial and initial-boundary value formulations of Einstein’s equations, and we discuss multi-domain high-order finite difference and spectral methods to solve them.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a new review article on “Binary Neutron Star Mergers” by Joshua A. Faber and Frederic A. Rasio on July 4, 2012. Please find the abstract and further details below.

We are also pleased to announce that Living Reviews in Relativity received an impact factor of 17.462 in Thomson Reuters Journal Citation Report 2011, again leading the category Physics, Particles & Fields. Special thanks to all our authors for writing such excellent reviews!

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PUB.NO. lrr-2012-8
Faber, Joshua A. and Rasio, Frederic A.
“Binary Neutron Star Mergers”

ACCEPTED: 2012-05-22
PUBLISHED: 2012-07-04

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-8

ABSTRACT:
We review the current status of studies of the coalescence of binary neutron star systems. We begin with a discussion of the channels by which merging binaries form, and discuss the most recent observational and theoretical predictions for observable merger rates. Next, we turn to the quasi-equilibrium formalisms that are used to study binaries prior to the merger phase and to generate initial data for dynamical simulations, including a discussion of our current understanding of the physics they can reveal in their own right and how they have shaped our view of the orbital instability processes that can drive binaries to merger at the end of their lifetimes. Afterwards, we turn to the techniques used in dynamical simulations, including relativistic formalisms, (magneto)hydrodynamics, gravitational wave extraction techniques, and nuclear-density microphysical treatments. This is followed by a discussion of the simulations performed across the field to date, including the most recent results from both fully relativistic and/or microphysically-oriented simulations. Finally, we discuss the likely directions for the field as we transition from the first generation of gravitational wave interferometers to the second while supercomputers enter the petascale regime.

UPCOMING ARTICLES AT:
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This month, Living Reviews in Relativity has published two new articles, a major update of the review “Stationary Black Holes: Uniqueness and Beyond” by Piotr T. Chrusciel, Joao Lopes Costa, and Markus Heusler and a new article on “Dynamical Boson Stars” by Steven L. Liebling and Carlos Palenzuela.

Please find the abstracts and further details below.

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PUB.NO. lrr-2012-7
Chrusciel, Piotr T. and Lopes Costa, Joao and Heusler, Markus
“Stationary Black Holes: Uniqueness and Beyond”

ACCEPTED: 2012-03-29
PUBLISHED: 2012-05-29

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-7

ABSTRACT:
The spectrum of known black-hole solutions to the stationary Einstein equations has been steadily increasing, sometimes in unexpected ways. In particular, it has turned out that not all black hole equilibrium configurations are characterized by their mass, angular momentum and global charges. Moreover, the high degree of symmetry displayed by vacuum and electrovacuum black-hole space-times ceases to exist in self-gravitating non-linear field theories. This text aims to review some developments on the subject and to discuss them in the light of the uniqueness theorem for the Einstein–Maxwell system.

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PUB.NO. lrr-2012-6
Liebling, Steven L. and Palenzuela, Carlos
“Dynamical Boson Stars”

ACCEPTED: 2012-03-29
PUBLISHED: 2012-05-08

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-6

ABSTRACT:
The idea of stable, localized bundles of energy has strong appeal as a model for particles. In the 1950s, John Wheeler envisioned such bundles as smooth configurations of electromagnetic energy that he called geons, but none were found. Instead, particle-like solutions were found in the late 1960s with the addition of a scalar field, and these were given the name boson stars. Since then, boson stars find use in a wide variety of models as sources of dark matter, as black hole mimickers, in simple models of binary systems, and as a tool in finding black holes in higher dimensions with only a single killing vector. We discuss important varieties of boson stars, their dynamic properties, and some of their uses, concentrating on recent efforts.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity has published a new review article on “Quantum Measurement Theory in Gravitational-Wave Detectors” by Stefan L. Danilishin and Farid Ya. Khalili on April 26, 2012.

Please find the abstract and further details below.

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PUB.NO. lrr-2012-5
Danilishin, Stefan and Khalili, Farid Ya.
“Quantum Measurement Theory in Gravitational-Wave Detectors”

ACCEPTED: 2012-03-02
PUBLISHED: 2012-04-26

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-5

ABSTRACT:
The fast progress in improving the sensitivity of the gravitational-wave (GW) detectors, we all have witnessed in the recent years, has propelled the scientific community to the point, when quantum behaviour of such immense measurement devices as kilometer-long interferometers starts to matter. The time, when their sensitivity will be mainly limited by the quantum noise of light is round the corner, and finding the ways how to make it lower will become a necessity. Therefore the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of Standard Quantum Limit and the methods of its surmounting.

UPCOMING ARTICLES AT:
http://relativity.livingreviews.org/Articles/upcoming.html

Living Reviews in Relativity has published an update of the review “Gravitational-Wave Data Analysis. Formalism and Applications: The Gaussian Case” by Piotr Jaranowski and Andrzej Królak on March 9, 2012.

Please find the abstract and further details below.

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PUB.NO. lrr-2012-4
Jaranowski, Piotr A. and Królak, Andrzej
“Gravitational-Wave Data Analysis. Formalism and Applications: The Gaussian Case”

ACCEPTED: 2012-02-14
PUBLISHED: 2012-03-09

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-4

ABSTRACT:
The article reviews the statistical theory of signal detection in application to analysis of deterministic gravitational-wave signals in the noise of a detector. Statistical foundations for the theory of signal detection and parameter estimation are presented. Several tools needed for both theoretical evaluation of the optimal data analysis methods and for their practical implementation are introduced. They include optimal signal-to-noise ratio, Fisher matrix, false alarm and detection probabilities, ℱ-statistic, template placement, and fitting factor. These tools apply to the case of signals buried in a stationary and Gaussian noise. Algorithms to efficiently implement the optimal data analysis techniques are discussed. Formulas are given for a general gravitational-wave signal that includes as special cases most of the deterministic signals of interest.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published a new review article on “Brane Effective Actions, Kappa-Symmetry and Applications” by Joan Simón on 27 February 2012.

Please find the abstract and further details below.

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PUB.NO. lrr-2012-3
Simón, Joan
“Brane Effective Actions, Kappa-Symmetry and Applications”

ACCEPTED: 2012-01-09
PUBLISHED: 2012-02-27

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-3

ABSTRACT:
This is a review on brane effective actions, their symmetries and some of its applications. Its first part uncovers the Green-Schwarz formulation of single M- and D-brane effective actions focusing on kinematical aspects: the identification of their degrees of freedom, the importance of world volume diffeomorphisms and kappa symmetry, to achieve manifest spacetime covariance and supersymmetry, and the explicit construction of such actions in arbitrary on-shell supergravity backgrounds.

Its second part deals with applications. First, the use of kappa symmetry to determine supersymmetric world volume solitons. This includes their explicit construction in flat and curved backgrounds, their interpretation as BPS states carrying (topological) charges in the supersymmetry algebra and the connection between supersymmetry and Hamiltonian BPS bounds. When available, I emphasise the use of these solitons as constituents in microscopic models of black holes. Second, the use of probe approximations to infer about non-trivial dynamics of strongly coupled gauge theories using the AdS/CFT correspondence. This includes expectation values of Wilson loop operators, spectrum information and the general use of D-brane probes to approximate the dynamics of systems with small number of degrees of freedom interacting with larger systems allowing a dual gravitational description.

Its final part briefly discusses effective actions for N D-branes and M2-branes. This includes both SYM theories, their higher order corrections and partial results in covariantising these couplings to curved backgrounds, and the more recent supersymmetric Chern–Simons matter theories describing M2-branes using field theory, brane constructions and 3-algebra considerations.

UPCOMING ARTICLES AT:
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Living Reviews in Relativity has published major updates of the reviews on “Characteristic Evolution and Matching” by Jeffrey Winicour and on “Null Geodesic Congruences, Asymptotically-Flat Spacetimes and Their Physical Interpretation” by Timothy A. Adamo, Ezra T. Newman, and Carlos Kozameh in January 2012.

Please find the abstract and further details below.

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PUB.NO. lrr-2012-2
Winicour, Jeffrey
“Characteristic Evolution and Matching”

ACCEPTED: 2012-01-04
PUBLISHED: 2012-01-25

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-2

ABSTRACT:
I review the development of numerical evolution codes for general relativity based upon the characteristic initial value problem. Progress in characteristic evolution is traced from the early stage of 1D feasibility studies to 2D axisymmetric codes that accurately simulate the oscillations and gravitational collapse of relativistic stars and to current 3D codes that provide pieces of a binary black hole spacetime. Cauchy codes have now been successful at simulating all aspects of the binary black hole problem inside an artificially constructed outer boundary. A prime application of characteristic evolution is to extend such simulations to null infinity where the waveform from the binary inspiral and merger can be unambiguously computed. This has now been accomplished by Cauchy-characteristic extraction, where data for the characteristic evolution is supplied by Cauchy data on an extraction worldtube inside the artificial outer boundary. The ultimate application of characteristic evolution is to eliminate the role of this outer boundary by constructing a global solution via Cauchy-characteristic matching. Progress in this direction is discussed.

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PUB.NO. lrr-2012-1
Newman, Ezra Ted and Kozameh, Carlos and Adamo, Timothy M.
“Null Geodesic Congruences, Asymptotically-Flat Spacetimes and Their Physical Interpretation”

ACCEPTED: 2012-01-16
PUBLISHED: 2012-01-24

FULL ARTICLE AT:
http://www.livingreviews.org/lrr-2012-1

ABSTRACT:
A priori, there is nothing very special about shear-free or asymptotically shear-free null geodesic congruences. Surprisingly, however, they turn out to possess a large number of fascinating geometric properties and to be closely related, in the context of general relativity, to a variety of physically significant effects. It is the purpose of this paper to try to fully develop these issues.

This work starts with a detailed exposition of the theory of shear-free and asymptotically shear-free null geodesic congruences, i.e., congruences with shear that vanishes at future conformal null infinity. A major portion of the exposition lies in the analysis of the space of regular shear-free and asymptotically shear-free null geodesic congruences. This analysis leads to the space of complex analytic curves in an auxiliary four-complex dimensional space, H-space. They in turn play a dominant role in the applications.

The applications center around the problem of extracting interior physical properties of an asymptotically-flat spacetime directly from the asymptotic gravitational (and Maxwell) field itself, in analogy with the determination of total charge by an integral over the Maxwell field at infinity or the identification of the interior mass (and its loss) by (Bondi’s) integrals of the Weyl tensor, also at infinity.

More specifically, we will see that the asymptotically shear-free congruences lead us to an asymptotic definition of the center-of-mass and its equations of motion. This includes a kinematic meaning, in terms of the center-of-mass motion, for the Bondi three-momentum. In addition, we obtain insights into intrinsic spin and, in general, angular momentum, including an angular-momentum–conservation law with well-defined flux terms. When a Maxwell field is present, the asymptotically shear-free congruences allow us to determine/define at infinity a center-of-charge world line and intrinsic magnetic dipole moment.

UPCOMING ARTICLES AT:
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