Conjecture on PG-shell Lefschetz chains for projective embeddings

Let XX be a complex projective manifold of dimension n>0n>0, let j:XP=PN(C)j:X\hookrightarrow P=\mathbb{P}^{N}(\mathbb{C}) be an arithmetically normal embedding, and let {Wp}p=0n\{W_p\}_{p=0}^n and {Wp}p=0n\{W_p^*\}_{p=0}^n be suitably chosen Lefschetz and dual Lefschetz chains of j(X)j(X). A PG-shell Lefschetz-chain conjecture asserts that the chains can be chosen so that each WpW_p and WpW_p^* is a PG-shell of j(X)j(X), reduced along j(X)j(X), and irreducible; each restricted conormal sheaf

NWp/Wp1XN^{\vee}_{W_p/W_{p-1}}|_X

is a vector bundle on XX extendable to Wp1W_{p-1} as a vector bundle, and likewise

NWp/Wp+1XN^{\vee}_{W_p^*/W_{p+1}^*}|_X

is a vector bundle extendable to Wp+1W_{p+1}^* as a vector bundle. Moreover, for a fixed manifold XX of dimension n2n\geq 2, one can suitably choose the embedding and the two chains so that a refinement of either chain realizes the Working Hypothesis referred to in the source.

Sources & referencesView supporting material

Primary source

Takeshi Usa, “Problems on geometric structures of projective embeddings”, arXiv:math/0001004 (2000).

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