C A MANTICA

L G MOLINARI

U C DE

Fulltext

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Erratum: “A condition for a perfect-fluid space-time to be a generalized Robertson-Walker space-time” [J. Math. Phys. 57, 022508 (2016)]

Journal of Mathematical Physics

Generalized Robertson-Walker (GRW) spacetime is the generalization of the Robertson-Walker (RW) spacetime and a further generalization of GRW spacetime is the twisted spacetime. In this paper, we generalize the results of the paper [C. A. Mantica, Y. J. Suh and U. C. De, A note on generalized Robertson-Walker spacetimes, Int. J. Geom. Methods Mod. Phys. 13 (2016), Article Id: 1650079, 9 pp., doi:101142/s0219887816500791]. We prove that a Ricci simple Lorentzian manifold with vanishing quasi-conformal curvature tensor is a RW spacetime. Further, we prove that a Ricci simple Lorentzian manifold with harmonic quasi-conformal curvature tensor is a GRW spacetime. As a consequence, we obtain several corollaries. Finally, we have cited some examples of the obtained results. © 2019 World Scientific Publishing Company.

International Journal of Geometric Methods in Modern Physics

Some characterizations of Lorentzian manifolds

The object of the present paper is to study almost pseudo-Q-symmetric manifolds A(PQS)n. Some geometric properties have been studied which recover some known results of pseudo Q-symmetric manifolds. We obtain a necessary and sufficient condition for the-curvature tensor to be recurrent in A(PQS)n. Also, we provide several interesting results. Among others, we prove that a Ricci symmetric A(PQS)n is an Einstein manifold under certain condition. Moreover we deal with-flat perfect fluid, dust fluid and radiation era perfect fluid spacetimes respectively. As a consequence, we obtain some important results. Finally, we consider A(PQS)4-spacetimes. © 2018 World Scientific Publishing Company.

Almost pseudo-Q-symmetric semi-Riemannian manifolds

The object of the present paper is to study mixed quasi-Einstein manifolds. Some geometric properties of mixed quasi-Einstein manifolds have been studied. We also discuss M(QE)4 spacetime with space-matter tensor and some properties related to it. Finally, we construct an example of a mixed quasi-Einstein spacetime. © 2017 World Scientific Publishing Company.

Characterizations of mixed quasi-Einstein manifolds

The object of the present paper is to study weakly cyclic Z symmetric spacetimes. At first we prove that a weakly cyclic Z symmetric spacetime is a quasi Einstein spacetime. Then we study (WCZS) 4 spacetimes satisfying the condition div C= 0. Next we consider conformally flat (WCZS) 4 spacetimes. Finally, we characterise dust fluid and viscous fluid (WCZS) 4 spacetimes. © 2016, Akadémiai Kiadó, Budapest, Hungary.

Acta Mathematica Hungarica

On weakly cyclic Z symmetric spacetimes

A perfect-fluid space-time of dimension n ≥ 4, with (1) irrotational velocity vector field and (2) null divergence of the Weyl tensor, is a generalised Robertson-Walker space-time with an Einstein fiber. Condition (1) is verified whenever pressure and energy density are related by an equation of state. The contraction of the Weyl tensor with the velocity vector field is zero. Conversely, a generalized Robertson-Walker space-time with null divergence of the Weyl tensor is a perfect-fluid space-time. © 2016 AIP Publishing LLC.

Journal	Data powered by TypesetJournal of Mathematical Physics
Publisher	Data powered by TypesetAmerican Institute of Physics Inc.
ISSN	0022-2488
Open Access	Yes