On the structure of complete 3-manifolds with nonnegative scalar curvature

In this paper we will show the following result: Let $\mathcal{N}$ be a complete (noncompact) connected orientable Riemannian three-manifold with nonnegative scalar curvature $S \geq 0$ and bounded sectional curvature $K_{s} \leq K$. Suposse that $\Sigma \subset \mathcal{N}$ is a complete orientable connected area-minimizing cylinder so that $\pi_1 (\Sigma) \in \pi_1 (\mathcal{N})$. Then $\mathcal{N}$ is locally isometric either to $\mathbb{S} ^1 \times \mathbb{R} ^2$ or $\mathbb{S}^1 \times \mathbb{S}^1 \times \mathbb{R}$ (with the standard product metric). As a corollary, we will obtain: Let $\mathcal{N}$ be a complete (noncompact) connected orientable Riemannian three-manifold with nonnegative scalar curvature $S \geq 0$ and bounded sectional curvature $K_{s} \leq K$. Assume that $\pi_1 (\mathcal{N})$ contains a subgroup which is isomorphic to the fundamental group of a compact surface of positive genus. Then, $\mathcal{N}$ is locally isometric to $\mathbb{S}^1 \times \mathbb{S}^1 \times \mathbb{R}$ (with the standard product metric).