scholarly journals Gravastars in a non-minimally coupled gravity with electromagnetism

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Özcan Sert ◽  
Muzaffer Adak
Keyword(s):  
Dark Energy ◽  
Exact Solutions ◽  
Free Parameter ◽  
Maxwell Model ◽  
Spherically Symmetric ◽  
Minimal Models ◽  
Coupled Models ◽  
Gravitational Fields ◽  
Gravitational Vacuum ◽  
Physical Quantities

AbstractIn this paper we investigate the gravitational vacuum stars which called gravastars in the non-minimally coupled models with electromagnetic and gravitational fields. We consider two non-minimal models and find the corresponding spherically symmetric exact solutions in the interior of the star consisting of the dark energy condensate. Our models turn out to be Einstein–Maxwell model at the outside of the star and the solutions become the Reissner–Nordström solution. The physical quantities of these models are continuous and non-singular in some range of parameters and the exterior geometry continuously matches with the interior geometry at the surface. We calculate the matter mass, the total gravitational mass, the electric charge and redshift of the star for the two models. We notice that these quantities except redshift are dependent of a subtle free parameter, k, of the model. We also remark a wide redshift range from zero to infinity depending on one free parameter, $$\beta $$ β , in the second model.

Spherically Symmetric Gravitational Fields

1965 ◽  
Vol 6 (1) ◽  
pp. 1-5 ◽  
Author(s):  
P. G. Bergmann ◽  
M. Cahen ◽  
A. B. Komar
Keyword(s):  
Spherically Symmetric ◽  
Gravitational Fields

scholarly journals PARAMETRIC INSTABILITY IN SCALAR GRAVITATIONAL FIELDS

2012 ◽  
Vol 27 (24) ◽  
pp. 1230023 ◽  
Author(s):  
TREVOR B. DAVIES ◽  
CHARLES H.-T. WANG ◽  
ROBERT BINGHAM ◽  
J. TITO MENDONÇA
Keyword(s):  
Gravitational Field ◽  
Field Effect ◽  
Strong Field ◽  
Parametric Instability ◽  
Spherically Symmetric ◽  
Scalar Tensor Theory ◽  
Subsequent Work ◽  
Dynamical Mechanism ◽  
Gravitational Fields ◽  
Tensor Theory

We present a brief review on a new dynamical mechanism for a strong field effect in scalar–tensor theory. Starting with a summary of the essential features of the theory and subsequent work by several authors, we analytically investigate the parametric excitation of a scalar gravitational field in a spherically symmetric radially pulsating neutron star.

scholarly journals A Magnetized Dark Energy Type R/W Model with Polytropic Equation of State in Brans-Dicke Theory

2020 ◽  
Vol 12 (3) ◽  
pp. 251-257
Author(s):  
M. Dewri
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Variable Cosmological Constant ◽  
Volumetric Expansion ◽  
Dynamical Behaviors ◽  
Tensor Theory ◽  
Polytropic Equation ◽  
Theory Of Gravitation ◽  
Energy Type ◽  
Physical Quantities

In this paper, we study the spatially homogeneous Robertson-Walker cosmological models with magnetized isotropic dark energy like fluid in the scalar-tensor theory of gravitation proposed by Brans-Dicke. Variable cosmological constant ᴧ and Polytropic equation of state have been used to find exact solutions of the models with volumetric expansion and power-law relation. The Physical and dynamical behaviors of the models have been discussed using some physical quantities like energy density, pressure, and coefficient of bulk viscosity.

scholarly journals The theory of spherically symmetric thin shells in conformal gravity

2018 ◽  
Vol 27 (06) ◽  
pp. 1841012 ◽  
Author(s):  
Victor Berezin ◽  
Vyacheslav Dokuchaev ◽  
Yury Eroshenko
Keyword(s):  
General Relativity ◽  
Weyl Tensor ◽  
Delta Function ◽  
Einstein Gravity ◽  
Riemann Tensor ◽  
Momentum Tensor ◽  
Thin Shells ◽  
Spherically Symmetric ◽  
Gravitational Fields ◽  
Gravitational Theories

The spherically symmetric thin shells are the nearest generalizations of the point-like particles. Moreover, they serve as the simple sources of the gravitational fields both in General Relativity and much more complex quadratic gravity theories. We are interested in the special and physically important case when all the quadratic in curvature tensor (Riemann tensor) and its contractions (Ricci tensor and scalar curvature) terms are present in the form of the square of Weyl tensor. By definition, the energy–momentum tensor of the thin shell is proportional to Diracs delta-function. We constructed the theory of the spherically symmetric thin shells for three types of gravitational theories with the shell: (1) General Relativity; (2) Pure conformal (Weyl) gravity where the gravitational part of the total Lagrangian is just the square of the Weyl tensor; (3) Weyl–Einstein gravity. The results are compared with these in General Relativity (Israel equations). We considered in detail the shells immersed in the vacuum. Some peculiar properties of such shells are found. In particular, for the traceless ([Formula: see text] massless) shell, it is shown that their dynamics cannot be derived from the matching conditions and, thus, is completely arbitrary. On the contrary, in the case of the Weyl–Einstein gravity, the trajectory of the same type of shell is completely restored even without knowledge of the outside solution.

scholarly journals SPIN-1 GRAVITATIONAL WAVES: THEORETICAL AND EXPERIMENTAL ASPECTS

2006 ◽  
Vol 03 (03) ◽  
pp. 451-469 ◽  
Author(s):  
F. CANFORA ◽  
L. PARISI ◽  
G. VILASI
Keyword(s):  
Physical Properties ◽  
Exact Solutions ◽  
Gravitational Waves ◽  
Lie Algebra ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Gravitational Fields ◽  
Killing Fields

Exact solutions of Einstein field equations invariant for a non-Abelian bidimensional Lie algebra of Killing fields are described. Physical properties of these gravitational fields are studied, their wave character is checked by making use of covariant criteria and the observable effects of such waves are outlined. The possibility of detection of these waves with modern detectors, spherical resonant antennas in particular, is sketched.

scholarly journals A class of solitons in Maxwell-scalar and Einstein–Maxwell-scalar models

2020 ◽  
Vol 80 (1) ◽  
Author(s):  
Carlos A. R. Herdeiro ◽  
João M. S. Oliveira ◽  
Eugen Radu
Keyword(s):  
Electromagnetic Field ◽  
Scalar Field ◽  
Quantum Gravity ◽  
Exact Solutions ◽  
Point Charge ◽  
Coulomb Field ◽  
Specific Class ◽  
Minimal Coupling ◽  
Flat Spacetime ◽  
Physical Quantities

AbstractRecently, no-go theorems for the existence of solitonic solutions in Einstein–Maxwell-scalar (EMS) models have been established (Herdeiro and Oliveira in Class Quantum Gravity 36(10):105015, 2019). Here we discuss how these theorems can be circumvented by a specific class of non-minimal coupling functions between a real, canonical scalar field and the electromagnetic field. When the non-minimal coupling function diverges in a specific way near the location of a point charge, it regularises all physical quantities yielding an everywhere regular, localised lump of energy. Such solutions are possible even in flat spacetime Maxwell-scalar models, wherein the model is fully integrable in the spherical sector, and exact solutions can be obtained, yielding an explicit mechanism to de-singularise the Coulomb field. Considering their gravitational backreaction, the corresponding (numerical) EMS solitons provide a simple example of self-gravitating, localised energy lumps.

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