Vanishing of Rabinowitz Floer homology on negative line bundles
Peter Albers, Jungsoo Kang
TL;DR
The paper constructs Rabinowitz Floer homology for negative line bundles over symplectic bases under a semi-positivity assumption and proves vanishing results in several natural regimes, highlighting that SH need not vanish in these settings. It develops a carefully restricted transversality framework and a Morse-Bott perturbation to define RFH, then employs a filtration to reduce the vanishing problem to fiberwise Floer trajectories, which vanish due to known RFH calculations on $S^1$-fibers. The results elucidate a nuanced distinction between RFH and SH beyond the symplectically aspherical case and suggest a conceptual explanation via the CFO-Oancea long exact sequence, with concrete implications for examples like negative line bundles over projective spaces. The work broadens RFH construction to settings with holomorphic spheres and provides a concrete mechanism for when RFH must vanish, enriching the landscape of symplectic invariants for negative line bundles.
Abstract
Following [Fra08, AF14] we construct Rabinowitz Floer homology for negative line bundles over symplectic manifolds and prove a vanishing result. In [Rit14] Ritter showed that symplectic homology of these spaces does not vanish, in general. Thus, the theorem $\mathrm{SH}=0\Leftrightarrow\mathrm{RFH}=0$, [Rit13], does not extend beyond the symplectically aspherical situation. We give a conjectural explanation in terms of the Cieliebak-Frauenfelder-Oancea long exact sequence [CFO10].
