
A \((J^ 4=1)\)-structure on an \(n\)-dimensional manifold \(M\) is a tensor field of type \((1,1)\) on \(M\) such that \(J^ 4=1\). Its characteristic polynomial is \((x-1)^{r_ 1}(x+1)^{r_ 2}(x^ 2+1)^ s\), where \(r_ 1+r_ 2+s=n\). In particular, one obtains the almost complex structure, the almost product structure and the almost hyperbolic complex structure (i.e. \(J^ 2=1\), \(J\neq \pm 1\) and \(r_ 1=r_ 2)\). Moreover, a \((J^ 4=1)\)-structure is metric if there is a pseudo-Riemannian structure \(g\) on \(M\) such that either (1) \(J\) is symmetric with respect to \(g\) or (2) \(J\) is skew- symmetric with respect to \(g\). In particular, one gets the almost Hermitian structure, the almost Riemannian product structure,the almost hyperbolic Hermitian structure (i.e. \(J^ 2-1\) and \(g\) satisfy (2) [\textit{P. Libermann}, Ann. Mat. Pura Appl., IV. Ser. 36, 27--120 (1954; Zbl 0056.15401)], \(e\)-metric \((J^ 4=1)\)-structure (i.e. \(J^ 4=1\) and \(g\) satisfies (2)). An \(e\)-metric \((J^ 4=1)\)-manifold is an \(e\)-(J\({}^ 4=1)\)-Kähler one if \({\bar \nabla}J=0\), where \({\bar \nabla}\) is the Levi-Cività connection of \(g\). The particular case when \(J^ 2=1\) was introduced by \textit{P. K. Rashevskii} [Tr. Semin. Vektorn. Tenzorn. Anal. 6, 225--248 (1948)]. In the present paper, the \(e-(J^ 4=1)\)-Kähler manifolds of constant \(J\)-sectional curvature are studied by extending the case exposed by \textit{M. S. Prvanović} [Math. Balk. 1, 195--213 (1971; Zbl 0221.53062)] and a theorem of Schur type is given. Also, it is shown that any two complex connected and simply connected \(e-(J^ 4=1)\)-Kähler manifolds of constant and equal \(J\)-sectional curvature are \(J\)-isometric. Models of para-Kähler manifolds are constructed here. As an \(e-(J^ 4=1)\)-Kähler manifold is locally the product of a hyperbolic Kähler manifold and a Kähler manifold, it follows that some models of \(e-(J^ 4=1)\)-Kähler manifolds can be obtained.
53C15, almost product structure, almost Hermitian structure, almost complex structure, \(e-(J^ 4=1)\)-Kähler manifolds, General geometric structures on manifolds (almost complex, almost product structures, etc.), almost hyperbolic complex structure, theorem of Schur type
53C15, almost product structure, almost Hermitian structure, almost complex structure, \(e-(J^ 4=1)\)-Kähler manifolds, General geometric structures on manifolds (almost complex, almost product structures, etc.), almost hyperbolic complex structure, theorem of Schur type
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