scholarly journals COLD BLACK HOLES AND CONFORMAL CONTINUATIONS

2008 ◽  
Vol 17 (01) ◽  
pp. 25-42 ◽  
Author(s):  
K. A. BRONNIKOV ◽  
M. S. CHERNAKOVA ◽  
J. C. FABRIS ◽  
N. PINTO-NETO ◽  
M. E. RODRIGUES
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Infinite Horizon ◽  
Einstein Gravity ◽  
Spherically Symmetric ◽  
Four Dimensions ◽  
Phantom Scalar ◽  
New Type ◽  
Theories Of Gravity ◽  
Phantom Scalar Field

We study Einstein gravity minimally coupled to a scalar field in a static, spherically symmetric space–time in four dimensions. Black hole solutions are shown to exist for a phantom scalar field whose kinetic energy is negative. These "scalar black holes" have an infinite horizon area and zero Hawking temperature and are termed "cold black holes" (CBHs). The relevant explicit solutions are well known in the massless case (the so-called anti-Fisher solution), and we have found a particular example of a CBH with a nonzero potential V(ϕ). All CBHs with V(ϕ) ≢ 0 are shown to behave near the horizon, quite similarly to those with a massless field. The above solutions can be converted by a conformal transformation to Jordan frames of a general class of scalar–tensor theories of gravity, but CBH horizons in one frame are in many cases converted to singularities in the other, which gives rise to a new type of conformal continuation.

scholarly journals Null and Timelike Geodesics near the Throats of Phantom Scalar Field Wormholes

Universe ◽  
2020 ◽  
Vol 6 (10) ◽  
pp. 183
Author(s):  
Ivan Potashov ◽  
Julia Tchemarina ◽  
Alexander Tsirulev
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Circular Orbit ◽  
Realistic Model ◽  
Test Particles ◽  
Stable Circular Orbit ◽  
Phantom Scalar ◽  
Metric Function ◽  
Bound Orbits ◽  
Phantom Scalar Field

We study geodesic motion near the throats of asymptotically flat, static, spherically symmetric traversable wormholes supported by a self-gravitating minimally coupled phantom scalar field with an arbitrary self-interaction potential. We assume that any such wormhole possesses the reflection symmetry with respect to the throat, and consider only its observable “right half”. It turns out that the main features of bound orbits and photon trajectories close to the throats of such wormholes are very different from those near the horizons of black holes. We distinguish between wormholes of two types, the first and second ones, depending on whether the redshift metric function has a minimum or maximum at the throat. First, it turns out that orbits located near the centre of a wormhole of any type exhibit retrograde precession, that is, the angle of pericentre precession is negative. Second, in the case of high accretion activity, wormholes of the first type have the innermost stable circular orbit at the throat while those of the second type have the resting-state stable circular orbit in which test particles are at rest at all times. In our study, we have in mind the possibility that the strongly gravitating objects in the centres of galaxies are wormholes, which can be regarded as an alternative to black holes, and the scalar field can be regarded as a realistic model of dark matter surrounding galactic centres. In this connection, we discuss qualitatively some observational aspects of results obtained in this article.

scholarly journals A study of phantom scalar field cosmology using Lie and Noether symmetries

2016 ◽  
Vol 25 (05) ◽  
pp. 1650051 ◽  
Author(s):  
Sourav Dutta ◽  
Subenoy Chakraborty
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Einstein Gravity ◽  
Matter Field ◽  
Lie Symmetry ◽  
Kinetic Term ◽  
Noether Symmetries ◽  
Phantom Scalar ◽  
Scalar Field Cosmology ◽  
Phantom Scalar Field

The paper deals with phantom scalar field cosmology in Einstein gravity. At first, using Lie symmetry, the coupling function to the kinetic term and the potential function of the scalar field and the equation of state parameter of the matter field are determined and a simple solution is obtained. Subsequently, Noether symmetry is imposed on the Lagrangian of the system. The symmetry vector is obtained and the potential takes a very general form from which potential using Lie symmetry can be obtained as a particular case. Then, we choose a point transformation [Formula: see text] such that one of the transformed variables (say [Formula: see text]) is a cyclic for the Lagrangian. Using conserved charge (corresponding to the cyclic coordinate) and the constant of motion, solutions are obtained.

scholarly journals Comment on “A study of phantom scalar field cosmology using Lie and Noether symmetries”

2016 ◽  
Vol 25 (14) ◽  
pp. 1675001
Author(s):  
Andronikos Paliathanasis ◽  
Spyros Basilakos ◽  
Michael Tsamparlis
Keyword(s):  
Dynamical System ◽  
Scalar Field ◽  
Coordinate System ◽  
Coordinate Transformation ◽  
Noether Symmetries ◽  
Phantom Scalar ◽  
Scalar Field Cosmology ◽  
Phantom Scalar Field

We show that the recent results of [S. Dutta and S. Chakraborty, Int. J. Mod. Phys. D 25 (2016) 1650051] on the application of Lie/Noether symmetries in scalar field cosmology are well-known in the literature while the problem could have been solved easily under a coordinate transformation. That follows from the property, that the admitted group of invariant transformations of dynamical system is independent on the coordinate system.

scholarly journals Nutty black holes in Galileon scalar-tensor gravity

2018 ◽  
Vol 33 (32) ◽  
pp. 1850189 ◽  
Author(s):  
A. Brandelet ◽  
Y. Brihaye ◽  
T. Delsate ◽  
L. Ducobu
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Einstein Gravity ◽  
Parameter Family ◽  
Hairy Black Holes ◽  
Two Parameter ◽  
Bonnet Term

Einstein gravity supplemented by a scalar field nonminimally coupled to a Gauss–Bonnet term provides an example of model of scalar-tensor gravity where hairy black holes do exist. We consider the classical equations within a metric endowed with a NUT-charge and obtain a two-parameter family of nutty-hairy black holes. The pattern of these solutions in the exterior and the interior of their horizon is studied in some details. The influence of both — the hairs and the NUT-charge — on the lightlike and timelike geodesics is emphasized.

scholarly journals Rotating wormhole solutions with a complex phantom scalar field

2019 ◽  
Vol 100 (4) ◽  
Author(s):  
Xiao Yan Chew ◽  
Burkhard Kleihaus ◽  
Jutta Kunz ◽  
Vladimir Dzhunushaliev ◽  
Vladimir Folomeev
Keyword(s):  
Scalar Field ◽  
Phantom Scalar ◽  
Phantom Scalar Field
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