Stable auto-equivalences for local symmetric algebras

We construct nontrivial auto-equivalences of stable module categories for elementary, local symmetric algebras over a field k  . These auto-equivalences are modeled after the spherical twists of Seidel and Thomas and the PnPn-twists of Huybrechts and Thomas, which yield auto-equivalences of the derived category of coherent sheaves on a variety. For group algebras of p-groups in characteristic p we recover many of the auto-equivalences corresponding to endo-trivial modules. We also obtain analogous auto-equivalences for local algebras of dihedral and semi-dihedral type, which are not group algebras.