## Welcome to SPP 2026

This is the platform of a coordinated research programme in mathematics, funded by the German Research Foundation (DFG). It comprises 33 research projects in the fields of differential geometry, geometric topology, and global analysis. More than 80 researchers from doctoral to professorial level and based at more than 20 German and Swiss universities are represented in this programme.

### SPP 2026 kick-off meeting in Potsdam

The kick-off meeting took place in the Audimax of the University of Potsdam, Campus am Neuen Palais, November 9-10, 2017.

## Next Activities

## Latest publications

#### S-arithmetic spinor groups with the same finite quotients and distinct ℓ²-cohomology

Holger Kammeyer, Roman Sauer

In this note we refine examples by Aka from arithmetic to S-arithmetic groups to show that the vanishing of the *i*-th ℓ²-Betti number is not a...

#### Profinite commensurability of S-arithmetic groups

Holger Kammeyer

Given an S-arithmetic group, we ask how much information on the ambient algebraic group, number field of definition, and set of places S is encoded in...

#### Wave and Dirac equations on manifolds

Lars Andersson, Christian Bär

We review some recent results on geometric equations on Lorentzian manifolds such as the wave and Dirac equations. This includes well-posedness and...

#### Convex projective surfaces with compatible Weyl connection are hyperbolic

Thomas Mettler, Gabriel P. Paternain

We show that a properly convex projective structure p on a closed oriented surface of negative Euler characteristic arises from a Weyl connection if...