Semi-factorial models and Néron models

Let S be the spectrum of a discrete valuation ring with function field K. Let X be a scheme over S. We will say that X is semi-factorial over S if each invertible sheaf on the generic fiber X_K can be extended to an invertible sheaf on X. Here we show that any proper geometrically normal scheme over K admits a model over S which is proper, flat, normal and semi-factorial. We also construct some semi-factorial compactifications of regular S-schemes, such as Néron models of abelian varieties. Moreover, the semi-factoriality property for a scheme X/S corresponds to the Néron property of its Picard functor. In particular, one can recover the Néron model of the Picard variety of X_K from the Picard functor of X/S, as in the case of curves. This provides some information about relative algebraic equivalence on the S-scheme X.

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