Four-dimensional steady gradient Ricci solitons with 3-cylindrical tangent flows at infinity

In this paper we consider 4-dimensional steady soliton singularity models, i.e., complete gradient Ricci solitons that arise as the rescaled limit of a finite time singular solution flow on closed 4-manifold. particular, study geometry at infinity such under assumption their tangent is product R with 3-dimensional spherical space form. We also classify flows models in general.