scholarly journals Corners of gravity: the case of gravity as a constrained BF theory

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Remigiusz Durka ◽  
Jerzy Kowalski-Glikman
Keyword(s):  
Cosmological Constant ◽  
Boundary Structure ◽  
Schwarzschild Solution ◽  
Bf Theory ◽  
Theory Of Gravity

Abstract Following recent works on corner charges we investigate the boundary structure in the case of the theory of gravity formulated as a constrained BF theory. This allows us not only to introduce the cosmological constant, but also explore the influence of the topological terms present in the action of this theory. Established formulas for charges resemble previously obtained ones, but we show that they are affected by the presence of the cosmological constant and topological terms. As an example we discuss the charges in the case of the AdS-Schwarzschild solution and we find that the charges give correct values.

scholarly journals Asymptotically flat vacuum solution in modified theory of Einstein’s gravity

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Surajit Kalita ◽  
Banibrata Mukhopadhyay
Keyword(s):  
General Relativity ◽  
Vacuum Solution ◽  
Compact Objects ◽  
Schwarzschild Solution ◽  
Asymptotically Flat ◽  
Symmetric Vacuum ◽  
Theory Of Gravity ◽  
Bound Orbits ◽  
Vacuum Spacetime ◽  
The Universe

Abstract A number of recent observations have suggested that the Einstein’s theory of general relativity may not be the ultimate theory of gravity. The f(R) gravity model with R being the scalar curvature turns out to be one of the best bet to surpass the general relativity which explains a number of phenomena where Einstein’s theory of gravity fails. In the f(R) gravity, behaviour of the spacetime is modified as compared to that of given by the Einstein’s theory of general relativity. This theory has already been explored for understanding various compact objects such as neutron stars, white dwarfs etc. and also describing evolution of the universe. Although researchers have already found the vacuum spacetime solutions for the f(R) gravity, yet there is a caveat that the metric does have some diverging terms and hence these solutions are not asymptotically flat. We show that it is possible to have asymptotically flat spherically symmetric vacuum solution for the f(R) gravity, which is different from the Schwarzschild solution. We use this solution for explaining various bound orbits around the black hole and eventually, as an immediate application, in the spherical accretion flow around it.

scholarly journals OBSERVABLE QUANTITIES IN WEYL GRAVITY

2011 ◽  
Vol 26 (32) ◽  
pp. 2403-2410 ◽  
Author(s):  
MOHAMMAD REZA TANHAYI ◽  
MOHSEN FATHI ◽  
MOHAMMAD VAHID TAKOOK
Keyword(s):  
Cosmological Constant ◽  
Linear Approximation ◽  
Hubble Parameter ◽  
Current State ◽  
Weyl Gravity ◽  
Weyl Theory ◽  
Theory Of Gravity ◽  
The Universe ◽  
Good Agreement

In this paper, the cosmological "constant" and the Hubble parameter are considered in the Weyl theory of gravity, by taking them as functions of r and t, respectively. Based on this theory and in the linear approximation, we obtain the values of H0 and Λ0 which are in good agreement with the known values of the parameters for the current state of the universe.

scholarly journals A SMALL BUT NONZERO COSMOLOGICAL CONSTANT

2001 ◽  
Vol 10 (01) ◽  
pp. 49-55 ◽  
Author(s):  
Y. JACK NG ◽  
H. VAN DAM
Keyword(s):  
Cosmological Constant ◽  
Scale Factor ◽  
Cosmological Constant Problem ◽  
Cosmic Scale ◽  
Theory Of Gravity ◽  
The Way

Recent astrophysical observations seem to indicate that the cosmological constant is small but nonzero and positive. The old cosmological constant problem asks why it is so small; we must now ask, in addition, why it is nonzero (and is in the range found by recent observations), and why it is positive. In this essay, we try to kill these three metaphorical birds with one stone. That stone is the unimodular theory of gravity, which is the ordinary theory of gravity, except for the way the cosmological constant arises in the theory. We argue that the cosmological constant becomes dynamical, and eventually, in terms of the cosmic scale factor R(t), it takes the form Λ(t)=Λ(t0)(R(t0)/R(t))2, but not before the epoch corresponding to the redshift parameter z~1.

Theory of gravity with the Dirac scalar field and the problem of cosmological constant

2012 ◽  
Vol 55 (7) ◽  
pp. 855-857 ◽  
Author(s):  
O. V. Babourova ◽  
K. N. Lipkin ◽  
B. N. Frolov
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Theory Of Gravity

scholarly journals Decaying Cosmological Constant and the Choice of a Conformal Frame

1999 ◽  
Vol 183 ◽  
pp. 310-310
Author(s):  
Yasunori Fujii
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Scalar Tensor Theory ◽  
Nonminimal Coupling ◽  
Tensor Theory ◽  
Theory Of Gravity ◽  
To Come ◽  
Hilbert Action

A solution of the cosomlogical constant problem seems to come from a version of the scalar-tensor theory of gravity, which is characterized by a “nonminimal coupling“ in place of the standard Einstein-Hilbert action, where ɸ is the scalar field while ξ a constant. One then encounters an inherent question never fully answered: How can one single out a right conformai frame?

Further spherically symmetric solutions

2021 ◽  
pp. 249-259
Author(s):  
Andrew M. Steane
Keyword(s):  
Black Hole ◽  
Field Equation ◽  
Cosmological Constant ◽  
Electromagnetic Fields ◽  
Stellar Structure ◽  
Spherically Symmetric ◽  
De Sitter ◽  
Schwarzschild Solution ◽  
Spherically Symmetric Solutions ◽  
Structure Equations

We obtain the interior Schwarzschild solution; the stellar structure equations (Tolman-Oppenheimer-Volkoff); the Reissner-Nordstrom metric (charged black hole) and the de Sitter-Schwarzschild metric. These both illustrate how the field equation is tackled in non-vacuum cases, and bring out some of the physics of stars, electromagnetic fields and the cosmological constant.

scholarly journals Cosmological Bounce and Some Other Solutions in Exponential Gravity

Universe ◽  
2018 ◽  
Vol 4 (10) ◽  
pp. 105 ◽  
Author(s):  
Pritha Bari ◽  
Kaushik Bhattacharya ◽  
Saikat Chakraborty
Keyword(s):  
Cosmological Constant ◽  
Cosmological Solution ◽  
Constant Term ◽  
Gravity Theory ◽  
De Sitter ◽  
Sitter Solution ◽  
Higher Derivative ◽  
New Type ◽  
Theories Of Gravity ◽  
Theory Of Gravity

In this work, we present some cosmologically relevant solutions using the spatially flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime in metric f ( R ) gravity where the form of the gravitational Lagrangian is given by 1 α e α R . In the low curvature limit this theory reduces to ordinary Einstein-Hilbert Lagrangian together with a cosmological constant term. Precisely because of this cosmological constant term this theory of gravity is able to support nonsingular bouncing solutions in both matter and vacuum background. Since for this theory of gravity f ′ and f ″ is always positive, this is free of both ghost instability and tachyonic instability. Moreover, because of the existence of the cosmological constant term, this gravity theory also admits a de-Sitter solution. Lastly we hint towards the possibility of a new type of cosmological solution that is possible only in higher derivative theories of gravity like this one.

Unimodular theory of gravity and the cosmological constant

1991 ◽  
Vol 32 (5) ◽  
pp. 1337-1340 ◽  
Author(s):  
Y. Jack Ng ◽  
H. van Dam
Keyword(s):  
Cosmological Constant ◽  
Theory Of Gravity
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