The LSC conjecture for families

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Let φ:Y→T\varphi: Y \to T be a flat morphism, let a\mathfrak{a} be an R\mathbb{R}-ideal sheaf on YY, and let τ:T→Y\tau: T \to Y be a section of φ\varphi. For a closed point t∈Tt \in T, set Yt=φ−1(t)Y_t = \varphi^{-1}(t) and at=aOYt\mathfrak{a}_t = \mathfrak{a}\mathcal{O}_{Y_t}. Suppose that for all t∈Tt \in T, at≠0\mathfrak{a}_t \ne 0 and YtY_t is a normal Q\mathbb{Q}-Gorenstein variety. LSC conjecture for families. The function

∣T∣cl→R≥0∪{−∞},t↦mld⁡τ(t)(Yt,at)|T|_{\rm cl} \to \mathbb{R}_{\ge 0} \cup \{-\infty\}, \qquad t \mapsto \operatorname{mld}_{\tau(t)}(Y_t,\mathfrak{a}_t)

is lower semi-continuous, where ∣T∣cl|T|_{\rm cl} is the set of closed points of TT with the Zariski topology. This conjecture is known when φ\varphi is smooth and when all fibers have only quotient singularities, but the general statement is open.

References

Primary source

Yusuke Nakamura and Kohsuke Shibata, “A counterexample to the PIA conjecture for minimal log discrepancies”, arXiv:2404.06164 (2026).

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