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Four-dimensional homogeneous manifolds satisfying some Einstein-like conditions. (English) Zbl 1455.53072

Let \((M^n, g)\) be an \(n\)-dimensional Riemannian manifold and \(R\), \(\rho\) and \(\tau\) be the curvature operator, Ricci tensor and scalar curvature, respectively. We define the following \((0,2)\)-tensors: \(\check{R}_{ij}=R_{iabc}R_j^{\ abc}\), \(\check{\rho}_{ij}=\rho_{ia}\rho_j^a\) and \(R[\rho]_{ij}=R_{iabj}\rho^{ab}\). These tensor fields provide natural Riemannian invariants, algebraically the simplest after the Ricci tensor. We say that \((M, g)\) is: \(\check{R}\)-Einstein if \(\check{R}= \frac 14 \|R\|^2 g\), \(\check{\rho}\)-Einstein if \(\check{\rho}= \frac 14 \|\rho\|^2 g\) and \(R[\rho]\)-Einstein if \(R[\rho]= \frac 14 \|\rho\|^2 g\). Since any of the three conditions is strictly weaker than being Einstein, we will say that a Riemannian manifold \((M, g)\) is weakly-Einstein if it satisfies at least one of the \(\check{R}\)-Einstein, \(\check{\rho}\)-Einstein or \(R[\rho]\)-Einstein conditions. The weakly-Einstein conditions appear naturally in the study of critical metrics for quadratic curvature functionals. Homogeneous Einstein metrics in dimension four were classified by Jensen. The aim of this paper is to extend Jensen’s classification to the weakly-Einstein situation. Note that the classification of homogeneous \(\check{R}\)-Einstein four-manifolds was obtained in paper [T. Arias-Marco and O. Kowalski, Czech. Math. J. 65, No. 1, 21–59 (2015; Zbl 1363.53032)].

MSC:

53C25 Special Riemannian manifolds (Einstein, Sasakian, etc.)
58E11 Critical metrics
53B20 Local Riemannian geometry
53C30 Differential geometry of homogeneous manifolds

Citations:

Zbl 1363.53032

References:

[1] Y.Euh,J.ParkandK.Sekigawa,A curvature identity on a 4-dimensional Riemannian manifold,Result. Math.63(2013), 107-114. · Zbl 1273.53009
[2] Y. Euh, J. Park and K. Sekigawa,Curvature identities derived from the integral formula for the first Pontrjagin number,Di¤erential Geom. Appl.31(2013), 463-471. · Zbl 1279.53032
[3] Y. Euh, J. Park and K. Sekigawa,Critical metrics for quadratic functionals in the curvature on 4-dimensional manifolds,Di¤erential Geom. Appl.29(2011), 642-646. · Zbl 1228.58010
[4] E.Garci´a-Ri´o,A.Haji-Badali,R.Marin˜ o-VillarandM.E.Va´ zquez-Abal,Locally conformally flat weakly-Einstein manifolds,Arch. Math. (Basel)111(2018), 549-559. · Zbl 1402.53012
[5] E.Garci´a-Ri´o,A.Haji-Badali,R.Marin˜ o-VillarandM.E.Va´ zquez-Abal,Structure of locally conformally flat manifolds satisfying some weakly-Einstein conditions,in preparation.
[6] A. Gray and T. J. Willmore,Mean-value theorems for Riemannian manifolds,Proc. Roy. Soc. Edinburgh Sect. A92(1982), 343-364. · Zbl 0495.53040
[7] G. S. Hall,Some remarks on the converse of Weyl’s conformal theorem,J. Geom. Phys. 60(2010), 1-7. · Zbl 1183.53065
[8] G.R.Jensen,Homogeneous Einstein spaces of dimension four,J. Di¤erential Geometry 3(1969), 309-349. · Zbl 0194.53203
[9] R. S. Kulkarni,Curvature and metric,Ann. of Math. (2)91(1970), 311-331. · Zbl 0191.19903
[10] M.-L.Labbi,Variational properties of the Gauss-Bonnet curvatures,Calc. Var. Partial Di¤erential Equations32(2008), 175-189. · Zbl 1139.58009
[11] J.Milnor,Curvatures of left invariant metrics on Lie groups,Adv. Math.21(1976), 293-329. · Zbl 0341.53030
[12] H.
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