Extremal problems related to Betti numbers of flag complexes

Understand

We study the problem of maximizing Betti numbers of simplicial complexes.

• We prove an upper bound of 1.32^n for the sum of Betti numbers of any n-vertex flag complex and 1.25^n for the independence complex of a triangle-free graph.
• These findings imply upper bounds for the Betti numbers of various related classes of spaces, including the neighbourhood complex of a graph.
• We also make some related observations.