Cohomogeneity one K\"ahler-Ricci solitons under a Heisenberg group action and related metrics

Abstract

We show that integrability of an almost complex structure in complex dimension $m$ is equivalent, in the presence of an almost hermitian metric, to $m(m-1)$ equations involving what we call shear operators. Inspired by this, we give an ansatz for K\"ahler metrics in dimension $m>1$, for which at most $m-1$ of these shear equations are non-trivial. The equations for gradient K\"ahler-Ricci solitons in this ansatz are frame dependent PDEs, which specialize to ODEs under extra assumptions. Metrics solving the latter system include a restricted class of cohomogeneity one metrics, and we find among them complete expanding gradient K\"ahler-Ricci solitons under the action of the $(2m-1)$-dimensional Heisenberg group, and some incomplete steady solitons. We examine curvature properties and asymptotics for the former Ricci solitons. In another special case of the ansatz we present, for $m=2$, a class of complete metrics of a more general type which we call gradient K\"ahler-Ricci skew-solitons, which are cohomogeneity one under the Euclidean plane group action. This paper continues research started in [MR, AM2].