Surfaces with parallel mean curvature in $\mathbb {C}P^n\times \mathbb {R}$ and $\mathbb {C}H^n\times \mathbb {R}$

Abstract:

We consider surfaces with parallel mean curvature vector (pmc surfaces) in $\mathbb {C}P^n\times \mathbb {R}$ and $\mathbb {C}H^n\times \mathbb {R}$, and, more generally, in cosymplectic space forms. We introduce a holomorphic quadratic differential on such surfaces. This is then used in order to show that the anti-invariant pmc $2$-spheres of a $5$-dimensional non-flat cosymplectic space form of product type are actually the embedded rotational spheres $S_H^2\subset \bar M^2\times \mathbb {R}$ of Hsiang and Pedrosa, where $\bar M^2$ is a complete simply-connected surface with constant curvature. When the ambient space is a cosymplectic space form of product type and its dimension is greater than $5$, we prove that an immersed non-minimal non-pseudo-umbilical anti-invariant $2$-sphere lies in a product space $\bar M^4\times \mathbb {R}$, where $\bar M^4$ is a space form. We also provide a reduction of codimension theorem for the pmc surfaces of a non-flat cosymplectic space form.