Orbifold and logarithmic structures provide independent routes to the virtual
enumeration of curves with tangency orders for a simple normal crossings
pair
.
The theories do not coincide and their relationship has remained mysterious.
We prove that the genus-zero orbifold theories of multiroot stacks of strata blowups
of
converge to the corresponding logarithmic theory of
. With
fixed numerical data, there is an explicit combinatorial criterion that guarantees
when a blowup is sufficiently refined for the theories to coincide. The result identifies
birational invariance as the crucial property distinguishing the logarithmic and
orbifold theories. There are two key ideas in the proof. The first is the construction
of a naive Gromov–Witten theory, which serves as an intermediary between roots and
logarithms. The second is a smoothing theorem for tropical stable maps; the geometric
theorem then follows via virtual intersection theory relative to the universal target.
The results import a new set of computational tools into logarithmic Gromov–Witten
theory. As an application, we show that the genus-zero logarithmic Gromov–Witten
theory of a pair is determined by the absolute Gromov–Witten theories of its strata.