Abstract
We prove that a four-dimensional compact oriented connected Riemannian manifold whose sectional curvatures all lie in the interval \([\frac{1}{1+3\sqrt{3}}, 1]\) is necessarily definite. In particular, we improve the pinching constants considered by some preceding works. In addition, we show that a four-dimensional compact oriented Einstein manifold whose sectional curvatures all lie in the interval \([\frac{1}{10}, 1]\) is either topologically \(\mathbb {S}^4\) or homothetically isometric to \(\mathbb {CP}^2,\) equipped with its standard Fubini-Study metric.
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The authors want to thank the referee for his careful reading, relevant remarks and valuable suggestions. Moreover, the authors want to thank E. Costa for helpful conversations about this subject.
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R. Diógenes was partially supported by FUNCAP/Brazil. E. Ribeiro Jr. was partially supported by CNPq/Brazil, Grant: 303091/2015-0.
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Diógenes, R., Ribeiro, E. Four-dimensional manifolds with pinched positive sectional curvature. Geom Dedicata 200, 321–330 (2019). https://doi.org/10.1007/s10711-018-0373-y
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DOI: https://doi.org/10.1007/s10711-018-0373-y