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:

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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.

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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:

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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:

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