8.3. Degenerations of Ricci-flat Kähler manifolds [0188]
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8.3. Degenerations of Ricci-flat Kähler manifolds
Let be a Ricci-flat Kähler manifold, i.e. a compact Kähler manifold with trivial first Chern class . Then carries a canonical probability measure , given by where is a Hermitian metric on with curvature (and hence unique up to a constant).
By the Calabi-Yau theorem, each Kähler -class on further contains a unique Ricci-flat Kähler metric , characterized by
Recall also that is torsion, i.e. for some positive integer . Indeed, this is a consequence of the Beauville-Bogomolov theorem [Beau83, Bog74], which implies that admits a finite étale cover with trivial. A trivializing section of defines a metric on as above, and hence .
As a consequence of Theorem A, we shall prove:
Theorem 8.5.
Let be a holomorphic family of Calabi-Yau Kähler manifolds , meromorphic at , and let be the corresponding family of canonical probability measures. For any snc model , converges in to a skeletal measure supported in .
Proof.
As recalled above, is torsion for each fixed . Equivalently, for some positive integer . Since is upper semicontinuous in the Zariski topology, it follows that is trivial for a fixed independent of . Given any snc model , is torsion free of rank one, and hence a line bundle. The choice of a trivializing section yields a holomorphic section of , inducing a holomorphic family of trivializing sections of for . As a consequence, the family of volume forms has analytic singularities at , and the result is thus a consequence of Theorem A, since . ∎