Resolution of singularities of the cotangent sheaf

Let X0X_0 be a reduced algebraic variety over a field of characteristic zero, or a reduced complex- or real-analytic variety, and let n=dimX0n=\dim X_0. A resolution of singularities is a proper birational or bimeromorphic morphism

σ:XX0\sigma:X\to X_0

such that XX is smooth, σ\sigma is an isomorphism over X0\SingX0X_0\backslash \operatorname{Sing} X_0, and σ1(SingX0)\sigma^{-1}(\operatorname{Sing} X_0) is the support of a simple normal crossings divisor EE on XX. In local analytic or étale coordinates (u,v)=(u1,,us,v1,,vns)(\mathbf u,\mathbf v)=(u_1,\ldots,u_s,v_1,\ldots,v_{n-s}) on XX, differential monomials are forms of the types d(uαi)d(\mathbf u^{\boldsymbol\alpha_i}) and d(uβjvj)d(\mathbf u^{\boldsymbol\beta_j}v_j). Resolution of singularities of the cotangent sheaf. There is a resolution of singularities σ:XX0\sigma:X\to X_0 such that the pulled-back cotangent sheaf of X0X_0 is locally generated by

d(uαi),i=1,,s,d(uβjvj),j=1,,ns,d(\mathbf u^{\boldsymbol\alpha_i}),\quad i=1,\ldots,s,\qquad d(\mathbf u^{\boldsymbol\beta_j}v_j),\quad j=1,\ldots,n-s,

where

suppE=(u1us=0),\operatorname{supp}E=(u_1\cdots u_s=0),

the multiindices α1,,αsNs\boldsymbol\alpha_1,\ldots,\boldsymbol\alpha_s\in\mathbb N^s are linearly independent over Q\mathbb Q, and {αi,βj}\{\boldsymbol\alpha_i,\boldsymbol\beta_j\} is totally ordered with respect to the componentwise partial ordering of Ns\mathbb N^s. This conjecture asks for a global resolution making the pulled-back cotangent sheaf monomial in suitable local coordinates; it is proved in dimensions up to three, while the general higher-dimensional case remains open.

Sources & referencesView supporting material

Primary source

Andre Belotto da Silva, Edward Bierstone, Vincent Grandjean and Pierre D. Milman, “Resolution of singularities of the cotangent sheaf of a singular variety”, arXiv:1504.07280 (2015).

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