Abstract
We study certain bi-scalar-tensor theories emanating from conformal symmetry requirements of Horndeski’s four-dimensional action. The former scalar is a Galileon with shift symmetry whereas the latter scalar is adjusted to have a higher order conformal coupling. Employing techniques from local Weyl geometry certain Galileon higher order terms are thus constructed to be conformally invariant. The combined shift and partial conformal symmetry of the action, allow us to construct exact black hole solutions. The black holes initially found are of planar horizon geometry embedded in anti de Sitter space and can accommodate electric charge. The conformally coupled scalar comes with an additional independent charge and it is well-defined on the horizon whereas additional regularity of the Galileon field is achieved allowing for time dependence. Guided by our results in adS space-time we then consider a higher order version of the BBMB action and construct asymptotically flat, regular, hairy black holes. The addition of the Galileon field is seen to cure the BBMB scalar horizon singularity while allowing for the presence of primary scalar hair seen as an independent integration constant along-side the mass of the black hole.
Highlights
Planar black holes with a cosmological constant and a Maxwell fieldWhere γ is a dimensionless coupling constant used to switch on and off the Maxwell field, and the last term is by construction conformally invariant (section 2)
Of the scalar field χ and its kinetic term X
The conformally coupled scalar comes with an additional independent charge and it is well-defined on the horizon whereas additional regularity of the Galileon field is achieved allowing for time dependence
Summary
Where γ is a dimensionless coupling constant used to switch on and off the Maxwell field, and the last term is by construction conformally invariant (section 2). The field equations for Ψ and φ are respectively (2.17) and (2.18), while for the metric we have. Taking the trace of (3.2) and using the field equation for φ, we get R = 4Λ from which we get, f (r). Conformal symmetry nicely (seems to) close in to a solution, the above is not in general a solution for the theory (3.1)
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