Overweight deformations of affine toric varieties and local uniformization

  • Bernard Teissier

    UMR 7586 du CNRS, Paris, France
Overweight deformations of affine toric varieties and local uniformization cover

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Given an equicharacteristic complete noetherian local ring RR with algebraically closed residue field kk, we first present a combinatorial proof of \emph{embedded} local uniformization for zero-dimensional valuations of RR whose associated graded ring grνR{\rm gr}_\nu R with respect to the filtration defined by the valuation is a finitely generated kk-algebra. The main idea here is that some of the birational toric maps which provide embedded pseudo-resolutions for the affine toric variety corresponding to grνR{\rm gr}_\nu R also provide local uniformizations for ν\nu on RR. These valuations are necessarily Abhyankar (for zero-dimensional valuations this means that the value group is Zr\mathbf Z^r with r=dimRr={\rm dim}R).\Par In a second part we show that conversely, given an excellent noetherian equicharacteristic local domain RR with algebraically closed residue field, if the zero-dimensional valuation ν\nu of RR is Abhyankar, there are local domains RR' which are essentially of finite type over RR and dominated by the valuation ring RνR_\nu (ν\nu-modifications of RR) such that the semigroup of values of ν\nu on RR' is finitely generated, and therefore so is the kk-algebra grνR{\rm gr}_\nu R'. Combining the two results and using the fact that Abhyankar valuations behave well under completion gives a proof of local uniformization for rational Abhyankar valuations and, by a specialization argument, for all Abhyankar valuations. \par As a by-product we obtain a description of the valuation ring of a rational Abhyankar valuation as an inductive limit indexed by N\mathbf N of birational toric maps of regular local rings. One of our main tools, the valuative Cohen theorem, is then used to study the extensions of rational monomial Abhyankar valuations of the ring k[[x1,,xr]]k[[x_1,\ldots ,x_r]] to monogenous integral extensions and the nature of their key polynomials. In the conclusion we place the results in the perspective of local embedded resolution of singularities by a single toric modification after an appropriate re-embedding.