scholarly journals ONCE AGAIN ON THIN-SHELL WORMHOLES IN SCALAR–TENSOR GRAVITY

2009 ◽  
Vol 24 (20) ◽  
pp. 1559-1564 ◽  
Author(s):  
KIRILL A. BRONNIKOV ◽  
ALEXEI A. STAROBINSKY
Keyword(s):  
Thin Shell ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Spherically Symmetric ◽  
Shell Surface ◽  
Symmetric Spacetimes ◽  
Tensor Theory ◽  
Thin Shell Wormholes ◽  
Spherically Symmetric Spacetimes ◽  
Static Spherically Symmetric Spacetimes

It is proved that all thin-shell wormholes built from two identical regions of vacuum static, spherically symmetric spacetimes have a negative shell surface energy density in any scalar–tensor theory of gravity with a non-ghost massless scalar field and a non-ghost graviton.

scholarly journals Could the black hole singularity be a field singularity?

2020 ◽  
Vol 29 (03) ◽  
pp. 2050026 ◽  
Author(s):  
Guillem Domènech ◽  
Atsushi Naruko ◽  
Misao Sasaki ◽  
Christof Wetterich
Keyword(s):  
Black Hole ◽  
Scalar Fields ◽  
Massless Scalar ◽  
Spherically Symmetric ◽  
Symmetric Spacetimes ◽  
Black Hole Singularity ◽  
Physical Singularity ◽  
Field Singularity ◽  
Spherically Symmetric Spacetimes ◽  
Static Spherically Symmetric Spacetimes

In the wake of interest to find black hole solutions with scalar hair, we investigate the effects of disformal transformations on static spherically symmetric spacetimes with a nontrivial scalar field. In particular, we study solutions that have a singularity in a given frame, while the action is regular. We ask if there exists a different choice of field variables such that the geometry and the fields are regular. We find that in some cases disformal transformations can remove a singularity from the geometry or introduce a new horizon. This is possible since the Weyl tensor is not invariant under a general disformal transformation. There exists a class of metrics which can be brought to Minkowksi geometry by a disformal transformation, which may be called disformally flat metrics. We investigate three concrete examples from massless scalar fields to Horndeski theory for which the singularity can be removed from the geometry. This might indicate that no physical singularity is present. We also propose a disformal invariant tensor.

Classification of Static Spherically Symmetric Spacetimes by Noether Symmetries

2013 ◽  
Vol 52 (10) ◽  
pp. 3534-3542 ◽  
Author(s):  
Ashfaque H. Bokhari ◽  
A. G. Johnpillai ◽  
A. H. Kara ◽  
F. M. Mahomed ◽  
F. D. Zaman
Keyword(s):  
Spherically Symmetric ◽  
Noether Symmetries ◽  
Symmetric Spacetimes ◽  
Spherically Symmetric Spacetimes ◽  
Static Spherically Symmetric Spacetimes

scholarly journals Bondi accretion in the spherically symmetric Johannsen–Psaltis spacetime

2019 ◽  
Vol 79 (11) ◽  
Author(s):  
Anslyn J. John ◽  
Chris Z. Stevens
Keyword(s):  
Accretion Rate ◽  
Kerr Metric ◽  
Spherically Symmetric ◽  
Gravitational Acceleration ◽  
Symmetric Spacetimes ◽  
Spherically Symmetric Spacetimes ◽  
Scalar Hair ◽  
Relativistic Analysis ◽  
Modified Theory ◽  
Static Spherically Symmetric Spacetimes

AbstractThe Johannsen–Psaltis spacetime explicitly violates the no-hair theorem. It describes rotating black holes with scalar hair in the form of parametric deviations from the Kerr metric. In principle, black hole solutions in any modified theory of gravity could be written in terms of the Johannsen–Psaltis metric. We study the accretion of gas onto a static limit of this spacetime. We utilise a recently proposed pseudo–Newtonian formulation of the dynamics around arbitrary static, spherically symmetric spacetimes. We obtain a potential that generalises the Paczyński–Wiita potential to the static Johannsen–Psaltis metric. We also perform a fully relativistic analysis of the geodesic equations in the static Johannsen–Psaltis spacetime. We find that positive (negative) values of the scalar hair parameter, $$\epsilon _{3}$$ϵ3, lower (raise) the accretion rate. Similarly, positive (negative) values of $$\epsilon _{3}$$ϵ3 reduce (increase) the gravitational acceleration of radially infalling massive particles.

scholarly journals Non-static spherically symmetric spacetimes and their conformal Ricci collineations

2019 ◽  
Vol 9 (2) ◽  
pp. 393-400 ◽  
Author(s):  
Fawad Khan ◽  
Tahir Hussain ◽  
Ashfaque Hussain Bokhari ◽  
Sumaira Saleem Akhtar
Keyword(s):  
Vector Field ◽  
Infinite Number ◽  
Ricci Tensor ◽  
Spherically Symmetric ◽  
Ricci Collineations ◽  
Symmetric Spacetimes ◽  
Integrability Conditions ◽  
Fluid Matter ◽  
Spherically Symmetric Spacetimes ◽  
Static Spherically Symmetric Spacetimes

Abstract For a perfect fluid matter, we present a study of conformal Ricci collineations (CRCs) of non-static spherically symmetric spacetimes. For non-degenerate Ricci tenor, a vector field generating CRCs is found subject to certain integrability conditions. These conditions are then solved in various cases by imposing certain restrictions on the Ricci tensor components. It is found that non-static spherically symmetric spacetimes admit 5, 6 or 15 CRCs. In the degenerate case, it is concluded that such spacetimes always admit infinite number of CRCs.

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