Stable logarithmic maps to Deligne-Faltings pairs I

We introduce a new compactification of the space of relative stable maps. This new method uses logarithmic geoemtry in the sense of Kato-Fontaine-Illusie rather than the expanded degeneration. The underlying structure of our log stable maps is stable in the usual sense.Comment: We changed the terminology "log stable maps" to "stable log maps". A gap in the proof of compatibility with formal completions pointed out by Professor Bernd Siebert has been fixed, see Section 2.7. Few minor changes in Lemma 3.3.8 and the proof of Lemma 6.5.1 are mad

Towards a Theory of Logarithmic GLSM Moduli Spaces

In this article, we establish foundations for a logarithmic compactification of general GLSM moduli spaces via the theory of stable log maps. We then illustrate our method via the key example of Witten's $r$-spin class. In the subsequent articles, we will push the technique to the general situation. One novelty of our theory is that such a compactification admits two virtual cycles, a usual virtual cycle and a "reduced virtual cycle". A key result of this article is that the reduced virtual cycle in the $r$-spin case equals to the r-spin virtual cycle as defined using cosection localization by Chang--Li--Li. The reduced virtual cycle has the advantage of being $\mathbb{C}^*$-equivariant for a non-trivial $\mathbb{C}^*$-action. The localization formula has a variety of applications such as computing higher genus Gromov--Witten invariants of quintic threefolds and the class of the locus of holomorphic differentials