Phenomenology of Scalar-Tensor Theories of Gravity  

In General > s.a. fifth force; higher-order gravity phenomenology; (post-)newtonian gravity.
* Idea: These theories in general agree with general relativity in the weak-field, slow-motion regime, but may differ significantly from it in strong-field situations; So far, the best constraints come from binary neutron stars; In the future we expect better binary-object constraints, and gravitational-wave ones.
* Scalar fields: In order to be astrophysically and cosmologically relevant they would have to be light.
* Weak equivalence principle: It is violated if there are types of matter that couple to different combinations of φ and gab.
@ General references: Esposito-Farèse AIP(04)gq [test, rev]; Lindroos et al PRD(16)-a1512 [propagation of scalar waves]; Alonso et al PRD(17)-a1610 [future cosmological experiments]; Sakstein & Jain PRL(17)-a1710, Baker et al PRL(17)-a1710, Langlois et al PRD(18)-a1711 [constraints from GW170817].
@ Lorentz symmetry violations: Bezerra et al PRD(05)ht/04 [with torsion]; Brax PLB(12) [environmentally dependent].
@ Solar system tests: Devi et al PRD(11)-a1104 [Dirac-Born-Infeld action]; Anderson & Yunes PRD(17)-a1705; Faraoni et al EPJC-a1906.
@ Binary systems: Freire et al MNRAS(12)-a1205 [the pulsar-white dwarf binary PSR J1738+0333]; Mirshekari & Will PRD(13)-a1301 [compact binaries to 2.5 PN order]; > s.a. neutron stars.
@ Quantum theory: Shojai et al MPLA(98), MPLA(98); > s.a. brans-dicke theory; quantum-gravity renormalization and asymptotic safety.
@ Other effects and results: Faraoni & Gunzig A&A(98) [light amplification]; Burton et al PLA(08)-a0711 [spinning particles]; Armendáriz-Picón & Penco PRD(12) [equivalence-principle violations]; Farajollahi et al PRD(11)-a1201; > s.a. equivalence principle; gravitational-constant variation; lensing.
> Cosmology: see cosmology in modified gravity; dark-energy models; quantum cosmology models.
> Gravitational waves: see gravitational radiation; gravitational-wave propagation.

Solutions > s.a. astrophysics [Buchdahl inequality]; Birkhoff Theorem; multipole moments; Q-Stars.
* Compact objects: Scalar-tensor theories can be compatible with Solar System experiments and still produce large modifications in the observable properties of neutron stars, such as masses and radii (Damour and Esposito-Farèse, 1990s); Black holes in these theories have no hair, but could grow "wigs" supported by time-dependent boundary conditions or spatial gradients; > s.a. neutron stars.
@ Black holes, hair: Bekenstein PRD(95); Cardoso et al PRL(13)-a1308 [and instabilities]; Sotiriou & Zhang PRL(14); Sotiriou & Zhou PRD(14)-a1408.
@ Black holes, other: Jacobson PRL(99)ap [primordial]; Stefanov et al MPLA(07)-a0708 [and non-linear electrodynamics]; Sotiriou & Faraoni PRL(12)-a1109 [stationary]; Cardoso et al PRD(13)-a1305 [scalarization and superradiant instability]; Rupert & Woolgar CQG(14)-a1310 [properties of horizons]; Bronnikov et al IJMPD(16)-a1603-conf.
@ Numerical models: Gerosa et al CQG(16)-a1602 [simulations of stellar collapse].
@ Other solutions: Moffat gq/07 [spherically symmetric, non-singular]; Sobreira et al JMP(09) [Einstein-Maxwell, static cylindrically symmetric]; Obukhov & Puetzfeld PRD(14)-a1404 [dynamics of extended test bodies, covariant multipolar approach]; > s.a. gravitating bodies [relativistic stars]; wormhole solutions.

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