Abstract
It follows from work of Perelman that any finite-time singularity of the Ricci flow on a compact $3$-manifold is modeled on an ancient $\varkappa$-solution.
We prove that every non-compact ancient $\varkappa$-solution in dimension $3$ is isometric to a family of shrinking cylinders (or a quotient thereof), or to the Bryant soliton. This confirms a conjecture of Perelman.
Citation
Simon Brendle. "Ancient solutions to the Ricci flow in dimension $3$." Acta Math. 225 (1) 1 - 102, September 2020. https://doi.org/10.4310/ACTA.2020.v225.n1.a1
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