Week 06.10.2025 – 12.10.2025

The induced Ramsey number $R_{ind}(H)$ of a graph $H$ is the minimum number $N$ such that there exists a graph with $N$ vertices for which all red/blue colorings of its edges contain a monochromatic induced copy of $H$. In this talk I'll show there exists an absolute constant $C > 0$ such that, for every graph $H$ on $k$ vertices, these numbers satisfy $R_{ind}(H) ≤ 2^{Ck}$. This resolves a conjecture of Erdős from 1975.

This is joint work with Lucas Aragão, Gabriel Dahia, Rafael Filipe and João Marciano

A Riemannian metric is said to be Einstein if it has constant Ricci curvature. In dimensions 2 or 3, this is actually equivalent requiring the metric to have constant sectional curvature. However, in dimensions 4 and higher, the Einstein condition becomes significantly weaker than constant sectional curvature, and this has rather dramatic consequences. In particular, it turns out that there are high-dimensional smooth closed manifolds that admit pairs of Einstein metrics with Ricci curvatures of opposite signs. After explaining how one constructs such examples, I will then discuss some recent results exploring the coexistence of Einstein metrics with zero and positive Ricci curvatures.