Logarithmic enumerative geometry for curves and sheaves
We propose a logarithmic enhancement of the Gromov-Witten/Donaldson-Thomas correspondence, with descendants, and study the behaviour of the correspondence under simple normal crossings degenerations. The formulation of the logarithmic correspondence requires a matching of tangency conditions and relative insertions. This is achieved via a version of the Nakajima basis for the cohomology of the Hilbert schemes of points on logarithmic surfaces. We then establish a strong form of the degeneration formula in logarithmic DT theory - the numerical DT invariants of the general fiber of a degeneration are determined by the numerical DT invariants attached to strata of the special fiber. The GW version of this result, which we also prove here, is a strengthening of the currently known formulas. A key role is played by a certain exotic class of insertions, introduced here, and can be thought of as non-local incidence conditions coupled across multiple boundary strata of the target geometry. Finally, we prove compatiblity of the new logarithmic GW/DT correspondence with degenerations, and in particular, knowledge of the conjecture on the strata of the special fiber of a degeneration implies it on the general fiber. Several examples are included to illustrate the nature and utility of the formula.