Curvature positivity for Kähler and quasi-Kähler flag manifolds

Abstract: In this paper, we study the notions of Griffiths and dual-Nakano positivity for the curvature of the Chern connection on K\"ahler and quasi-K\"ahler flag manifolds, as well as for the complex projective space. In this setting, we prove that every flag manifold endowed with a complex structure admits a metric of dual-Nakano semi-positive curvature, and we give a full classification of K\"ahler flag manifolds with Griffiths semi-positive curvature. Next we prove a series of restrictions for a quasi-K\"ahler flag manifold to have Griffiths semi-positive curvature, and we conjecture that in fact, there are no such metrics for non-integrable almost-complex structures. Lastly, we give a full classification on invariant metrics on the complex projective space with Griffiths and dual-Nakano semi-positive curvature.