Stationary configurations imply shift symmetry: no Bondi accretion for quintessence/k-essence

The Brans-Dicke-like field of scalar-tensor gravity can be described as an imperfect fluid in an approach in which the field equations are regarded as effective Einstein equations. After completing this approach we recover, as a special case, the known effective fluid for a scalar coupled nonminimally to the Ricci curvature and we describe the imperfect fluid equivalent of f (R) gravity. A symmetry of electrovacuum Brans-Dicke gravity is translated into a symmetry of the corresponding effective fluid. The discussion is valid for any spacetime geometry.

Section: Introductionmentioning

confidence: 99%

Imperfect fluid description of modified gravities

Faraoni

Côté

2018

“…For instance, in the ghost condensate model the attractor solution of the Friedmann equations is a de Sitter state with ϕ ∝ t, and so one might expect the scalar field around massive objects to necessarily evolve in time. There have in fact been several studies [37][38][39][40][41] which have investigated the accretion of a K-essence field onto a black hole (usually assuming the flow is steady state).…”

Section: Discussionmentioning

confidence: 99%

Nonexistence of black holes with noncanonical scalar fields

Graham

Jha

2014

We study the existence of black holes with a noncanonical scalar field as a matter source. We prove a simple no-hair theorem which rules out the existence of stationary, asymptotically flat black holes possessing scalar hair for a wide class of noncanonical scalar field theories. This applies to scalar field theories which are of the form of K-essence theories. In particular, we rule out the existence of such black holes in the ghost condensate model, and in large sectors of the dilatonic ghost condensate and Dirac-Born-Infeld models.

“…Otherwise, if c 1 Þ 0, there is no steady-state solution for the accretion (this is similar to the case of the k-essence field see, e.g. [20]). The constant c 2 in (2) is dimensionless, c 3 has dimension À3, in the context of the DGP model this coefficient is usually written as r c =M 2 Pl where r c is the so called crossover scale and M Pl is the Planck mass.…”

Section: Modelmentioning

confidence: 82%

“…Critical solution exists, Eq. (20), with the critical point at r Ã ¼ 3=4, see Fig. 1, upper (red) line.…”

Section: Resultsmentioning

confidence: 97%

See 1 more Smart Citation

Galileon accretion

Babichev

2011

We study steady-state spherically symmetric accretion of a galileon field onto a Schwarzschild black hole in the test fluid approximation. The galileon is assumed to undergo a stage of cosmological evolution, thus setting a non-trivial boundary condition at spatial infinity. The critical flow is found for some parameters of the theory. There is a range of parameters when the critical flow exists, but the solution is unstable. It is also shown that for a certain range of parameters the critical flow solution does not exist. Depending on the model the sound horizon of the flow can be either outside or inside of the Schwarzschild horizon. The latter property may make it problematic to embed the galileon theory in the standard black hole thermodynamics.Comment: 14 pages, 3 figures; v.3: matches published versio