Landsberg–Tommasi extension conjecture for Fano schemes of lines

Let KK be an algebraically closed field of characteristic zero, let Xn1PnX^{n-1}\subset \mathbb P^n be a hypersurface of degree nλn-\lambda, and let BF(X)B\subset \mathbb F(X) be an irreducible component of dimension n2n-2. Let IB\mathcal I_B and XBX_B be as above, and define C~x\widetilde{\mathcal C}_x as above. Landsberg–Tommasi extension conjecture. If

codim(XB,X)λ\operatorname{codim}(X_B,X)\geq\lambda

and Cx\mathcal C_x is reduced for general xXBx\in X_B, then for every xXBx\in X_B,

C~xXsing.\widetilde{\mathcal C}_x\cap X_{\mathrm{sing}}\neq\varnothing.

This extends the preceding singular-locus condition to smaller degrees under a codimension hypothesis and a reducedness assumption. The supplied text presents it as the authors' extension, but gives no resolution status.

Sources & referencesView supporting material

Primary source

J. M. Landsberg and Orsola Tommasi, “On the Debarre-de Jong and Beheshti-Starr conjectures on hypersurfaces with too many lines”, arXiv:0810.4158 (2008).

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