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ORIGINAL RESEARCH article
Front. Phys. , 03 October 2022
Sec. Statistical and Computational Physics
Volume 9 - 2021 | https://doi.org/10.3389/fphy.2021.800060
This article is part of the Research Topic Differential Geometric Methods in Modern Physics View all 7 articles
Parts of this article's content have been modified or rectified in:
Erratum: Spacetimes admitting concircular curvature tensor in f(R) gravity
The main object of this paper is to investigate spacetimes admitting concircular curvature tensor in f(R) gravity theory. At first, concircularly flat and concircularly flat perfect fluid spacetimes in
A concircular transformation was first coined by Yano in 1940 [1]. Such a transformation preserves geodesic circles. The geometry that deals with a concircular transformation is called concircular geometry. Under concircular transformation the concircular curvature tensor
In Einstein’s theory of gravity, the relation between the matter of spacetimes and the geometry of the spacetimes is given by Einstein’s field equations (EFE)
with κ being the Newtonian constant and
where
In a series of recent studies, weakly Ricci symmetric spacetimes (WRS)4, almost pseudo-Ricci symmetric spacetimes(APRS)4, and conformally flat generalized Ricci recurrent spacetimes are investigated in
This article is organized as follows. In Section 2, concircularly flat spacetimes in f(R) gravity are considered. In Section 3, we study concircularly flat perfect fluid spacetimes in f(R) gravity as well as we consider some energy conditions. Finally, spacetimes with divergence free concircular curvature tensor in f(R) gravity are investigated.
The concircular curvature tensor of type
where
Here, we will consider
This equation leads us to state the following theorem:
Theorem 1. A concircularly flat spacetime is of constant curvature.
Corollary 1. A concircularly flat spacetime is of constant scalar curvature.Contracting Eq. 2.2 with gjm, we get
In view of Eq. 2.3 we can state the following corollary:
Corollary 2. A concircularly flat spacetime is Einstein.In view of corollary 1, the field Eq. 1.1 in
In vacuum case, we have
Contracting with gij and integrating the result, one gets
where λ is a constant.Conversely, if Eq. 2.5 holds, then
We can thus state following theorem:
Theorem 2. A concircularly flat spacetime in
whereas ξ is called conformal Killing if
where
It is clear that every Killing vector field is a matter collineation, but the converse is not generally true. The energy-momentum tensor Tij has the Lie inheritance property along the flow lines of the vector field ξ if the Lie derivative of Tij with respect to ξ satisfies [15–17].
Now using Eq. 2.3 in Eq. 2.4, one gets
In a concircularly flat spacetime the scalar curvature R is constant, and hence f and f′ are also constants. Now, we consider a non-vacuum concircularly flat spacetime M. Therefore the Lie derivative
Assume that the vector field ξ is Killing on M, that is, Eq. 2.6 holds, thus we have
Conversely, if Eq. 2.8 holds, then form Eq. 2.11 it follows that
We thus motivate to state the following theorem:
Theorem 3. Let M be a concircularly flat spacetime satisfying
Corollary 3. A non-vacuum concircularly flat spacetime satisfying
Conversely, assume that Eq. 2.9 holds, then from Eq. 2.11 we obtain
Hence, we can state the following theorem:
Theorem 4. Let M be a concircularly flat spacetime satisfying
Since in a concircularly flat spacetime R is constant, then f and f′ are constant. Inserting Eq. 2.4 in Eq. 2.12, we get
Thus, we have:
Theorem 5. Let M be a concirculary flat spacetime satisfying
In a perfect fluid 4 − dimensional spacetime, the energy-momentum tensor
where p is the isotropic pressure, σ is the energy density, and ui is a unit timelike vector field [7, 23].
Making use of Eq. 3.1 in Eq. 2.4, we get
The use of Eq. 2.3 implies that
Contracting Eq. 3.3 with ui, we get
Transvecting Eq. 3.3 with gij and using Eq. 3.4, one obtains
In consequence of the above we can state the following theorem:
Theorem 6. In a concircularly flat perfect fluid spacetime obeying f(R) gravity, the isotropic pressure p and the energy density σ are constants and
which means that the spacetime represents dark matter era or alternatively the perfect fluid behaves as a cosmological constant [ [24]]. Thus we can state the following theorem:
Theorem 7. A concircularly flat perfect fluid spacetime obeying f(R) gravity represents dark matter era.In radiation era σ = 3p, therefor the energy-momentum tensor Tij takes the form
Eq. 3.6 implies that p = 0. It follows that
which means that the spacetime is devoid of matter.Thus we motivate to state the following corollary:
Corollary 4. Let M be a concircularly flat spacetime obeying
From Eq. 3.6 it follows that σ = 0. And consequently from Eq. 3.8 we infer
which means that the spacetime is vacuum.We thus can state the following:
Corollary 5. Let M be a concircularly flat dust fluid spacetime obeying
In this subsection, some energy conditions in concircularly flat spacetimes obeying
Eq. 2.4 may be rewritten as
where
This leads us to rewrite Eq. 3.1 in the following form
where
The use of Eq. 3.4 and Eq. 3.5 entails that
Let us investigate certain energy conditions of a perfect fluid type effective matter in
1) Null energy condition (NEC): it says that peff + σeff ≥ 0.
2) Weak energy condition (WEC): it states that σeff ≥ 0 and peff + σeff ≥ 0.
3) Dominant energy condition (DEC): it states that σeff ≥ 0 and peff ± σeff ≥ 0.
4) Strong energy condition (SEC): it states that σeff + 3peff ≥ 0 and peff + σeff ≥ 0.
In this context, all mentioned energy conditions are consistently satisfied if Rf’ ≥ 0. As mentioned earlier, f′ must be positive to ensure attractive gravity. Therefore, the previous energy conditions are always satisfied if R ≥ 0.
The divergence of the concircular curvature tensor, for n = 4, is given by [28].
It is well-known that
The use of Eq. 4.2 in Eq. 4.1 implies that
Assume that the concircular curvature tensor is divergence free, that is
Contracting with glm and using
Utilizing (4.5) in Eq. 4.4, we have
which means that the Ricci tensor is of Codazzi type [29]. The converse is trivial. Thus we can state the following theorem:
Theorem 8. Let M be a spacetime with concircular curvature tensor, then M has Codazzi type of Ricci tensor if and only if the concircular curvature tensor is divergence free.In view of Eq. 4.5, the field Eq. 1.1 in
Using Eq. 4.7 in Eq. 4.6, we get
Hence, we have the following corollary:
Corollary 6. The energy-momentum tensor of a spacetime with divergence free concircular curvature tensor obeying
whileas the energy-momentum tensor is called semi-symmetric if
Now, Eq. 4.7 implies
Thus, we can state the following theorem:
Theorem 9. Let M be a spacetime with divergence free concircular curvature tensor satisfying
whereas Tij is called bi-recurrent if there exists a non-zero tensor ɛhk such that
In view of the above definition, it is clear that every recurrent tensor field is bi-recurrent.Now assume that
Contracting with gij, we obtain
where
Taking the covariant derivative of Eq. 4.10 and utilizing Eq. 4.12, we get
It follows that
Similarly, the same result holds for a bi-recurrent
Lemma 1. A (bi-)recurrent
Theorem 10. Let M be a spacetime with divergence free concircular curvature tensor obeying
where
Making a contraction of Eq. 4.13 with gij, we get
Since the
Contracting with ui, we obtain
But
Equivalently, it is
This equation implies the following cases:
Case 1. If
Case 2. If b ≠ 0, then
Then a − b = 0. With the help of equation (4.14), we have
Using (4.16) in (4.15), we get
Theorem 11. Let the energy-momentum tensor of a perfect fluid spacetime with divergence free concircular curvature tensor obeying
1) The spacetime represents inflation, or
2) The isotropic pressure p and the energy density σ are constants. Moreover, they are given by Eq. 4.16 and Eq. 4.17.
In virtue of Eq. 4.16 and Eq. 4.17 we have
In view of the previous theorem we can state the following:
Remark 1. According to the different states of cosmic evolution of the Universe we can conclude that the spacetime with
The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding authors.
Conceptualization and methodology, SS, UD, AS, NT, HA-D, and SA; formal analysis, SS, UD and AS; writing original draft preparation, SS, AS and NT; writing-review and editing, SS, UD, HA-D, and SA; supervision, SS and UD; project administration, NT and AS; and funding acquisition, NT and SA. All authors have read and agreed to the published version of the manuscript.
This project was supported by the Researchers Supporting Project number (RSP2022R413), King Saud University, Riyadh, Saudi Arabia.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
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Keywords: perfect fluid, energy-momentum tensor, concircular curvature tensor, f (R) gravity theory, energy conditions in modified gravity
Citation: De UC, Shenawy S, Abu-Donia HM, Turki NB, Alsaeed S and Syied AA (2022) Spacetimes Admitting Concircular Curvature Tensor in f(R) Gravity. Front. Phys. 9:800060. doi: 10.3389/fphy.2021.800060
Received: 22 October 2021; Accepted: 09 December 2021;
Published: 12 January 2022.
Edited by:
Jae Won Lee, Gyeungsang National University, South KoreaReviewed by:
Peibiao Zhao, Nanjing University of Science and Technology, ChinaCopyright © 2022 De, Shenawy, Abu-Donia, Turki, Alsaeed and Syied. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Nasser Bin Turki, bmFzc2VydEBrc3UuZWR1LnNh; Abdallah Abdelhameed Syied, YS5hX3N5aWVkQHlhaG9vLmNvbQ==
Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.
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