Andreas Thom: "High-dimensional expansion and soficity of groups"

mardi 11 mars 2025, 14:00 → 15:00 Europe/Paris

435 (UMPA)

For d≥4 and p a sufficiently large prime, we construct a lattice Γ≤PSp_{2d}(ℚ_p), such that its universal central extension cannot be sofic if Γ satisfies some weak form of stability in permutations. In the proof, we make use of high-dimensional expansion phenomena and, extending results of Lubotzky, we construct new examples of cosystolic expanders over arbitrary finite abelian groups. (This is joint work with Lukas Gohla.)