A Pohozaev Identity on Warped Product Solitons

Warped product metrics are a class of Riemannian metrics on cross products $B \times F$ which have been well studied and provide a rich set of examples. In this paper we consider shrinking gradient Ricci solitons which are warped product metrics. We prove that if the curvature of the metric is bounded and the base $B$ has two dimensions, the metric must in fact be a cross product. The theorem is a consequence of a Pohozaev-type identity. This closely parallels results in the study of blow-ups of solutions to the reaction- diffusion equation $\partial_t v = \Delta v + e^v$ in $\mathbb{R}^2$ .