Abstract
We study a positivity condition for the curvature of oriented Riemannian 4-manifolds: the half-PIC condition. It is a slight weakening of the positive isotropic curvature (PIC) condition introduced by M. Micallef and J. Moore. We observe that the half-PIC condition is preserved by the Ricci flow and satisfies a maximality property among all Ricci flow invariant positivity conditions on the curvature of oriented 4-manifolds. We also study some geometric and topological aspects of half-PIC manifolds.
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Richard, T., Seshadri, H. Positive isotropic curvature and self-duality in dimension 4. manuscripta math. 149, 443–457 (2016). https://doi.org/10.1007/s00229-015-0790-2
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DOI: https://doi.org/10.1007/s00229-015-0790-2