Gravitational Radiation  

In General > s.a. detection [motivation for search]; analysis [including other theories of gravity]; graviton.
* Idea: Wavelike solutions of the linearized Einstein equation, propagating at the speed of light; Ripples in a reference spacetime.
* History: 1918, Einstein showed that the linearized equation admits such solutions; Many believed that they would not carry energy/momentum, although calculations showed they would; 1936, Einstein, Infeld & Rosen state that there are no gravitational waves, based on the belief that such solutions are singular (the paper was turned down by a PR referee who claimed it had mistakes; the referee was Robertson, Einstein was furious, and Robertson turned out to be right); 1949, Landau pseudotensor; 1950s, Bondi, Feynman argue that gravitational waves carry energy, and 1957 Chapel Hill Conference discussion; 1970s, Weber's bar detector; 1980s, Thorne, Damour, well-defined framework; > s.a. history of relativistic gravity.
* Evidence: 1999, Indirect, from the increase of the binary pulsar period (75 × 10−6 sec/yr); 2005, Better binary pulsar.
* Significance: Their existence supports the idea that spacetime is a real, physical entity, like water in a pool.
> Online resources: see Thorne et al Caltech 2002 web-based course; The Gravitational Lens newsletter; Marc Favata's Sounds of Spacetime.

Theory > s.a. asymptotic flatness at null infinity; gauge invariance; orbits of gravitating bodies [with radiation].
* Properties: Contrary to the previous opinion of some people, it carries energy and momentum (see news tensor, Bondi mass, etc); Even perturbatively, tmn(1) ≠ 0 for + and × polarizations; It has spin 2, as can be seen from (a) Linearization of the Einstein equation around gab = ηab; In the weak-field limit the spin appears as the eigenvalue of the corresponding Casimir operator; (b) Study of the asymptotic theory, for which the Poincaré group is an exact symmetry group.
* Characterization: A useful tool is the study of the spin coefficients in the Newman-Penrose formalism, or the Beetle-Burko radiation scalar, all constructed using the Weyl tensor (> see spin coefficients, weyl tensor).
* Mode decomposition: A global decomposition analogous to the E and B mode decomposition of electromagnetic waves, which corresponds to the even or odd parity of the sky pattern of the polarization of the radiation.
* Open questions: Do general solutions have the falloff required by the scri formalism? One does not start from Cauchy data and construct full solutions; An important thing is to try to remove symmetry requirements; Come up with a coordinate-invariant characterization of gravitational waves for spacetimes with a positive cosmological constant.
* In scalar-tensor gravity: Linearized gravitational waves in Brans-Dicke and scalar-tensor theories carry negative energy.
@ Properties: Trautman BAPS(58)-a1604 [energy flux, from Sommerfeld boundary conditions]; Walker & Dual gq/97 [longitudinal, near field]; Aldrovandi et al FP(07)-a0709 [importance of non-linearity]; Brink PRD(08)-a0807 [and spacetime reconstruction]; Price et al AJP(13)aug-a1212 [comparison with electromagnetic radiation]; Ashtekar & Bonga GRG(17)-a1707 [ambiguity in transverse traceless modes]; Chu & Liu CQG(20)-a1902 [acausality of TT gravitational waves]; Blanchet a1902-CRAS; Chang et al a2009 [second-order waves]; > s.a. propagation [including speed].
@ Scalar-tensor gravity: Scharre & Will PRD(02), Will & Yunes CQG(04) [LISA, waveforms]; Sotani & Kokkotas PRD(04)gq [neutron star seismology]; Faraoni PRD(04) [stability of Minkowski]; Yunes et al PRD(12)-a1112 [extreme-mass-ratio inspirals]; Sotani PRD(14)-a1402 [scalar waves from relativistic stars]; Lang JPCS(15)-a1408 [compact binaries]; Kuntz et al JCAP(19)-a1902 [effective theory]; > s.a. gravitational-wave background.
@ Higher-dimensional gravity: Cardoso et al PRD(03); Durrer & Kocian CQG(04) [quadrupole formula and binary pulsar]; Seahra et al PRL(05)gq/04 [branes, spectroscopy]; Alesci & Montani IJMPD(05)gq/04 [5D Kaluza-Klein], IJMPD(05); Clarkson & Maartens GRG(05)ap-GRF; Clarkson & Seahra CQG(07); McWilliams PRL(10)-a0912; Yagi et al PRD(11)-a1103 [braneworld gravity]; Andriot & Lucena JCAP(17)-a1704 [signatures]; Kwon et al a1906 [5D Kaluza-Klein modes]; Ganjali & Sedaghatmanesh a1910 [effects on LIGO]; Du et al a2004 [waveform]; > s.a. gravitational-wave background and sources.
@ Teleparallel gravity: Obukhov et al CQG(09)-a0909 [plane waves]; Sharif & Taj MPLA(10) [cylindrical and spherical waves]; Nashed ChPB(10)-a1101; Hohmann et al PRD(18)-a1807 [propagation].
@ Higher-order theories: Upadhye & Steffen a1306 [f(R) gravity, monopole radiation]; Lambiase et al JCAP(15)-a1503 [and damping of binary orbital period]; Gürses et al PRD(15)-a1509 [3D higher-derivative gravity]; Hölscher PRD(19)-a1806; Capozziello et al IJGMP(19)-a1812; Katsuragawa et al a1902 [f(R) gravity, scalar waves and Chameleon mechanism].
@ With torsion: Bamba et al PLB(13)-a1309 [f(T) gravity]; Blagojević & Cvetković PRD(14)-a1406 [3D]; Alves et al PRD(16)-a1604 [f(R,T) gravity]; Cai et al PRD(18)-a1801 [f(T), after GW170817 and GRB170817A].
@ Other theories of gravity: Mirshekari PhD(13)-a1308; > s.a. astrophysical tests of gravity; conformal gravity; gravitation [frameworks]; gravity theories [scalar-vector-tensor]; gravitational-wave analysis; MOND; phenomenology of hořava gravity.

Types and Effects > s.a. angular momentum; background; early-universe cosmology; propagation and sources; thermodynamics.
@ Polarization: Canfora et al PLB(02) [non-linear waves]; > s.a. gravitational-wave sources.
@ Energy-momentum: Abramo PRD(99)ap [very long wavelength]; Cooperstock AP(00)gq/99, MPLA(99)gq ["no E"]; Garecki AdP(02)gq/01; Sharif NCB(01)gq, IJMPA(02)gq/01 [example]; Dereli & Tucker CQG(04) [energy-momentum density]; Mannheim PRD(06)gq [covariant]; Ruiz et al GRG(08)-a0707 [multipole expansion]; Aldrovandi et al IJTP(10)-a0809; Abbassi & Mirshekari IJMPA(08)-a0908; Garecki a1612-conf.
@ Background-independent: Agresti et al GRG(04)gq/03, gq/03; Lusanna gq/04-conf, gq/04-ch.
@ Analog systems: Fernandez-Corbaton et al SRep(15)-a1406 [quantum emulation]; > s.a. emergent gravity [analog simulation].
@ Related topics: Preder & Yourgrau IJTP(77) [shock waves]; Schmidt PRS(87) [near infinity]; Burnett JMP(89) [high-f limit]; van Putten & Eardley PRD(96)gq/95 [as Yang-Mills waves]; Esposito CQG(01)gq [Green functions]; Stewart GRG(06) [shock waves]; Deffayet & Menou ApJL(07)-a0709 [spacetime sirens as probes of new gravity]; Bruschi & Fuentes a1607 [extracting energy]; > s.a. chaotic motion.

blue bullet Phenomenology: see astronomy [multimessenger astronomy]; electromagnetic waves; gravitational-wave solutions; petrov-pirani classification.

References > s.a. canonical quantum gravity; Penrose Inequality; quantum-gravity phenomenology; stress-energy pseudotensor.
@ Intros, reviews: in Heaviside 1894 [precursor]; Weber 61; Pirani in(65); Hawking CP(72), reprint CP(09); in Misner et al 73; Zakharov 73; Walker in(83); Schutz AJP(84)may, EAA(00)gq; Damour in(87); Thorne 91, in(95); Chakrabarty phy/99; Blanchet LNP(00)gq-in [post-newtonian]; Schutz & Ricci ln(01)-a1005 [sources and detection, pedagogical]; Gibbs SA(02)apr; Hughes AP(03)ap/02; Centrella AJP(03)RL-gq/02; Sathyaprakash gq/04-conf; Flanagan & Hughes NJP(05)gq; Maggiore gq/06-fs; Kennefick 07; Buonanno a0709-ln; Maggiore 08, 18; Sathyaprakash & Schutz LRR(09)-a0903; Creighton & Anderson 11; Farr et al AJP(12)-a1109 [in the high-school classroom]; Riles PPNP(13)-a1209; Cerdonio & Losurdo RNC(12)#8; Pereira a1305; Kuroda et al IJMPD(15)-a1511-ch [classification, detection, sources]; Le Tiec & Novak in(17)-a1607; Prasanna a1610; Chen et al ChJP(17)-a1610; van Holten a1611-proc; de Cesare et al FdP(17)-a1701-ln [as a tensor field in Minkowski spacetime]; Blanchet a1701; Bieri et al NAMS(17)-a1710 [overview of the mathematics]; Gasperini a1811 [IT]; McWilliams et al a1902 [status]; Cacciatori a2005.
@ Conferences: Smarr ed-79; Królak ed-97; Ciufolini et al ed-00; issue CQG(02)#7 [Amaldi 4]; issue CQG(03)#17 [analysis 7]; issue CQG(04)#5 [Amaldi 5]; issue CQG(04)#20 [analysis 8]; issue CQG(06)#8 [Amaldi 6]; issue CQG(07)#19 [analysis 11]; issue CQG(08)#11 [Amaldi 7]; issue CQG(08)#18 [analysis 12]; issue CQG(10)#8 [Amaldi 8]; issue CQG(10)#19 [analysis 14]; issue CQG(12)#12 [Amaldi 9, NRDA 2011]; > s.a. interferometers.
@ Gravitational Waves Notes: Amaro-Seoane et al a1002 [#2], a1005 [#3], a1009 [#4].
@ General references: Weber & Wheeler RMP(57); Bondi et al PRS(62); Sachs PR(62), PRS(62), in(64); Komar PR(64); Van der Burg PRS(66); Blanchet & Damour PTRS(86); Friedrich CMP(86); Blanchet PRS(87); Bondi & Pirani PRS(89); Blanchet et al LNP(01)gq/00; Ni MPLA(10)-a1003-proc [classification, space-based detectors and dark energy]; Centrella AIP(11)-a1109-TX25; Ferrando & Sáez CQG(12)-a1111 [Bel's radiative gravitational fields]; Andersson et al CQG(13)-a1305 [transient events, state of the art and challenges]; Collins a1607 [imitation game]; Rostworowski PRD(15)-a1705 [non-linear]; Romero FS-a1708, Dirkes IJMPA(18)-a1802 [conceptual]; Fernández-Álvarez & Senovilla a1909 [novel characterisation].
@ Different points of view: Denisov & Logunov TMP(80) [non-existence]; Burdet & Perrin LMP(92) [gravitons]; Loinger ap/98, ap/99, ap/99, ap/99/NCB, ap/99/NCC, NCB(00)ap, gq/00 [speed of thought!]; Marshall a0707; Chakalov's site; Pereira a1305 [conceptual issues].
@ And quantum theory: Ashtekar PRL(81), JMP(81), in(81) [asymptotic quantization]; Manoukian GRG(90); Lovas HIP(01)gq/99; Unnikrishnan & Gillies CQG(15)-a1508 [quantum-gravitational optics]; Cardoso et al PRD(16)-a1608, Agulló et al a2007 [gravitational-wave signatures].

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