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Limits of stable pairs

Valery Alexeev
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Abstract

Let (X_0,B_0) be the canonical limit of a one-parameter family of stable pairs, provided by the log Minimal Model Program. We prove that X_0 is S2 and that [B_0] is S_1, as an application of a general local statement: if (X,B+εD) is log canonical and D is Q-Cartier then D is S2 and [B] \cap D is S1, i.e. has no embedded components. When B has coefficients smaller than 1, examples due to Hacking and Hassett show that B_0 may indeed have embedded primes. We resolve this problem by introducing a category of stable branchpairs. We prove that the corresponding moduli functor is proper for families with normal generic fiber.

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Valery Alexeev. 2007-11-05. Limits of stable pairs. https://arxiv.org/abs/math/0607684

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