Global monopoles in f(R) gravity

2015 ◽  
Vol 30 (40) ◽  
pp. 1550217 ◽  
Author(s):  
Melis Ulu Dog̃ru ◽  
Dog̃ukan Taṣer
Keyword(s):  
Black Holes ◽  
Cold Dark Matter ◽  
Spherically Symmetric ◽  
Approximation Methods ◽  
Field Equations ◽  
Symmetric Spacetimes ◽  
Form Field ◽  
Spherically Symmetric Spacetimes ◽  
Global Monopoles ◽  
Static Spherically Symmetric Spacetimes

In this study, we investigate whether global monopoles cause black holes or wormholes to form. Field equations for static spherically symmetric spacetimes with global monopoles are obtained in [Formula: see text] gravity. We found exact solutions for the field equations without using any perturbation or approximation methods. It is shown that the obtained [Formula: see text] function is in accordance with the [Formula: see text]-cold dark matter ([Formula: see text]-CDM) model. Also, it is shown that the static spherically symmetric spacetimes associated with global monopoles form black holes or wormhole structures under some restrictions. Finally, geometrical and physical results of the solutions are discussed.

Final fate of charged anisotropic fluid collapse in f(R) gravity

2020 ◽  
Vol 35 (29) ◽  
pp. 2050238
Author(s):  
Suhail Khan ◽  
Muhammad Shoaib Khan ◽  
Amjad Ali
Keyword(s):  
Physical Significance ◽  
Anisotropic Fluid ◽  
Time Interval ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Closed Form Solutions ◽  
Symmetric Spacetimes ◽  
Apparent Horizons ◽  
Spherically Symmetric Spacetimes ◽  
Static Spherically Symmetric Spacetimes

In this paper, the spherically symmetric gravitational collapse of anisotropic fluid in the presence of charge in metric [Formula: see text] theory is analyzed. We consider the static and non static spherically symmetric spacetimes for outer and inner regions of collapsing object respectively. For the smooth matching of inner and outer regions, the Senovilla as well as Darmois matching conditions are utilized. The closed form solutions are obtained from field equations. Moreover, we examine the apparent horizons and their physical significance. The effect of cosmological constant and [Formula: see text] term is same and the collapsing rate speeds up as compared to that of anisotropic fluid case when the electromagnetic field is introduced. Electromagnetic charge also affects the time interval of singularities and cosmological horizons.

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 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.

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