We study the Ricci flow on $4$-manifolds admitting a cohomogeneity one group action, i.e. an isometric group action such that the orbit space $M/G$ is $1$-dimensional. We use this to demonstrate the first examples of 4-manifolds having nonnegative sectional curvature which under the Ricci flow, immediately acquire some negatively curved 2-planes. In particular, we show that $S^4$, $\mathbb{C}P^2$, $S^2\times S^2$ and $\mathbb{C}P^2 \# \overline{\mathbb{C}P^2}$ admit such metrics. This talk is based on joint work with Renato G. Bettiol.
Links:
[1] http://www.mpim-bonn.mpg.de/taxonomy/term/39
[2] http://www.mpim-bonn.mpg.de/node/3444
[3] http://www.mpim-bonn.mpg.de/node/6543