The LSC conjecture for families

Let φ:YT\varphi: Y \to T be a flat morphism, let a\mathfrak{a} be an R\mathbb{R}-ideal sheaf on YY, and let τ:TY\tau: T \to Y be a section of φ\varphi. For a closed point tTt \in T, set Yt=φ1(t)Y_t = \varphi^{-1}(t) and at=aOYt\mathfrak{a}_t = \mathfrak{a}\mathcal{O}_{Y_t}. Suppose that for all tTt \in T, at0\mathfrak{a}_t \ne 0 and YtY_t is a normal Q\mathbb{Q}-Gorenstein variety. LSC conjecture for families. The function

TclR0{},tmldτ(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 Tcl|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.

Sources & referencesView supporting material

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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