Generic transversality for unbranched covers of closed pseudoholomorphic curves

Abstract

We prove that in closed almost complex manifolds of any dimension, generic perturbations of the almost complex structure suffice to achieve transversality for all unbranched multiple covers of simple pseudoholomorphic curves with deformation index zero. A corollary is that the Gromov-Witten invariants (without descendants) of symplectic 4-manifolds can always be computed as a signed and weighted count of honest J-holomorphic curves for generic tame J: in particular, each such invariant is an integer divided by a weighting factor that depends only on the divisibility of the corresponding homology class. The transversality proof is based on an analytic perturbation technique, originally due to Taubes.

31 pages; v3 has improved exposition in several places, especially the discussion of normal perturbations of almost complex structures (section 3) and the Weitzenböck formula (section 5); to appear in CPAM