Phenomenology
of Scalar-Tensor
Theories of Gravity |

**In General **> s.a. cosmology;
gravitational radiation; 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 *g*_{ab}.

@ __General references__: Esposito-Farèse AIP(04)gq
[test, rev]; Lindroos et al PRD(16)-a1512
[propagation of scalar waves]; Alonso et al a1610 [future cosmological experiments]; Sakstein & Jain a1710, Baker et al a1710, Langlois et al 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 a1705.

@ __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; gravitational wave propagation; lensing.

**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-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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send feedback and suggestions to bombelli at olemiss.edu – modified 8 dec
2017