Non-Fillable Invariant Contact Structures On Principal Circle Bundles And Left-Handed Twists

We define symplectic fractional twists, which subsume Dehn twists and fibered twists and use these in open books to investigate contact structures. The resulting contact structures are invariant under a circle action, and share several similarities with the invariant contact structures that were studied by Lutz and Giroux. We show that left-handed fractional twists often give rise to "algebraically overtwisted" contact manifolds, a certain class of non-fillable contact manifolds.