• Title, Summary, Keyword: Einstein manifold

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ON WEAKLY EINSTEIN ALMOST CONTACT MANIFOLDS

  • Chen, Xiaomin
    • Journal of the Korean Mathematical Society
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    • v.57 no.3
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    • pp.707-719
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    • 2020
  • In this article we study almost contact manifolds admitting weakly Einstein metrics. We first prove that if a (2n + 1)-dimensional Sasakian manifold admits a weakly Einstein metric, then its scalar curvature s satisfies -6 ⩽ s ⩽ 6 for n = 1 and -2n(2n + 1) ${\frac{4n^2-4n+3}{4n^2-4n-1}}$ ⩽ s ⩽ 2n(2n + 1) for n ⩾ 2. Secondly, for a (2n + 1)-dimensional weakly Einstein contact metric (κ, μ)-manifold with κ < 1, we prove that it is flat or is locally isomorphic to the Lie group SU(2), SL(2), or E(1, 1) for n = 1 and that for n ⩾ 2 there are no weakly Einstein metrics on contact metric (κ, μ)-manifolds with 0 < κ < 1. For κ < 0, we get a classification of weakly Einstein contact metric (κ, μ)-manifolds. Finally, it is proved that a weakly Einstein almost cosymplectic (κ, μ)-manifold with κ < 0 is locally isomorphic to a solvable non-nilpotent Lie group.

EINSTEIN'S CONNECTION IN 3-DIMENSIONAL ES-MANIFOLD

  • HWANG, IN HO
    • Korean Journal of Mathematics
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    • v.23 no.2
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    • pp.313-321
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    • 2015
  • The manifold $^*g-ESX_n$ is a generalized n-dimensional Riemannian manifold on which the differential geometric structure is imposed by the unified field tensor $^*g^{{\lambda}{\nu}}$ through the ES-connection which is both Einstein and semi-symmetric. The purpose of the present paper is to prove a necessary and sufficient condition for a unique Einstein's connection to exist in 3-dimensional $^*g-ESX_3$ and to display a surveyable tnesorial representation of 3-dimensional Einstein's connection in terms of the unified field tensor, employing the powerful recurrence relations in the first class.

EINSTEIN'S CONNECTION IN 5-DIMENSIONAL ES-MANIFOLD

  • Hwang, In Ho
    • Korean Journal of Mathematics
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    • v.25 no.1
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    • pp.127-135
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    • 2017
  • The manifold $^*g-ESX_n$ is a generalized n-dimensional Riemannian manifold on which the differential geometric structure is imposed by the unified field tensor $^*g^{{\lambda}{\nu}}$ through the ES-connection which is both Einstein and semi-symmetric. The purpose of the present paper is to prove a necessary and sufficient condition for a unique Einstein's connection to exist in 5-dimensional $^*g-ESX_5$ and to display a surveyable tnesorial representation of 5-dimensional Einstein's connection in terms of the unified field tensor, employing the powerful recurrence relations in the first class.

SOME RESULTS IN η-RICCI SOLITON AND GRADIENT ρ-EINSTEIN SOLITON IN A COMPLETE RIEMANNIAN MANIFOLD

  • Mondal, Chandan Kumar;Shaikh, Absos Ali
    • Communications of the Korean Mathematical Society
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    • v.34 no.4
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    • pp.1279-1287
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    • 2019
  • The main purpose of the paper is to prove that if a compact Riemannian manifold admits a gradient ${\rho}$-Einstein soliton such that the gradient Einstein potential is a non-trivial conformal vector field, then the manifold is isometric to the Euclidean sphere. We have showed that a Riemannian manifold satisfying gradient ${\rho}$-Einstein soliton with convex Einstein potential possesses non-negative scalar curvature. We have also deduced a sufficient condition for a Riemannian manifold to be compact which satisfies almost ${\eta}$-Ricci soliton.

NONCONSTANT WARPING FUNCTIONS ON EINSTEIN WARPED PRODUCT MANIFOLDS WITH 2-DIMENSIONAL BASE

  • Lee, Soo-Young
    • Korean Journal of Mathematics
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    • v.26 no.1
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    • pp.75-85
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    • 2018
  • In this paper, we study nonconstant warping functions on an Einstein warped product manifold $M=B{\times}_{f^2}F$ with a warped product metric $g=g_B+f(t)^2g_F$. And we consider a 2-dimensional base manifold B with a metric $g_B=dt^2+(f^{\prime}(t))^2du^2$. As a result, we prove the following: if M is an Einstein warped product manifold with a 2-dimensional base, then there exist generally nonconstant warping functions f(t).

GRADIENT EINSTEIN-TYPE CONTACT METRIC MANIFOLDS

  • Kumara, Huchchappa Aruna;Venkatesha, Venkatesha
    • Communications of the Korean Mathematical Society
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    • v.35 no.2
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    • pp.639-651
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    • 2020
  • Consider a gradient Einstein-type metric in the setting of K-contact manifolds and (κ, µ)-contact manifolds. First, it is proved that, if a complete K-contact manifold admits a gradient Einstein-type metric, then M is compact, Einstein, Sasakian and isometric to the unit sphere 𝕊2n+1. Next, it is proved that, if a non-Sasakian (κ, µ)-contact manifolds admits a gradient Einstein-type metric, then it is flat in dimension 3, and for higher dimension, M is locally isometric to the product of a Euclidean space 𝔼n+1 and a sphere 𝕊n(4) of constant curvature +4.

ON EINSTEIN HERMITIAN MANIFOLDS II

  • Kim, Jae-Man
    • Bulletin of the Korean Mathematical Society
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    • v.46 no.2
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    • pp.289-294
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    • 2009
  • We show that on a Hermitian surface M, if M is weakly *-Einstein and has J-invariant Ricci tensor then M is Einstein, and vice versa. As a consequence, we obtain that a compact *-Einstein Hermitian surface with J-invariant Ricci tensor is $K{\ddot{a}}hler$. In contrast with the 4- dimensional case, we show that there exists a compact Einstein Hermitian (4n + 2)-dimensional manifold which is not weakly *-Einstein.

COMPACT KÄHLER-EINSTEIN 4-MANIFOLD

  • Kim, Mi-Ae
    • Korean Journal of Mathematics
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    • v.8 no.1
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    • pp.53-61
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    • 2000
  • The object of this paper is to find the 4-dimensional compact Einstein manifold with negative Ricci curvature $r$.

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