Toroidal embedding

In algebraic geometry, a toroidal embedding is an open embedding of algebraic varieties that locally looks like the embedding of the open torus into a toric variety. The notion was introduced by Mumford to prove the existence of semistable reductions of algebraic varieties over one-dimensional bases.

Definition

Let X be a normal variety over an algebraically closed field ${\bar {k}}$ and $U\subset X$ a smooth open subset. Then $U\hookrightarrow X$ is called a toroidal embedding if for every closed point x of X, there is an isomorphism of local ${\bar {k}}$-algebras:

${\widehat {\mathcal {O}}}_{X,x}\simeq {\widehat {\mathcal {O}}}_{X_{\sigma },t}$

for some affine toric variety $X_{\sigma }$ with a torus T and a point t such that the above isomorphism takes the ideal of $X-U$ to that of $X_{\sigma }-T$.

Let X be a normal variety over a field k. An open embedding $U\hookrightarrow X$ is said to a toroidal embedding if $U_{\bar {k}}\hookrightarrow X_{\bar {k}}$ is a toroidal embedding.

Examples

Tits' buildings

Main article: Tits' buildings

See also

• tropical compactification

References

• Kempf, G.; Knudsen, Finn Faye; Mumford, David; Saint-Donat, B. (1973), Toroidal Embeddings I, Lecture Notes in Mathematics, vol. 339, Berlin, New York: Springer-Verlag, doi:10.1007/BFb0070318, ISBN 978-3-540-06432-9, MR 0335518
• Abramovich, D., Denef, J. & Karu, K.: Weak toroidalization over non-closed fields. manuscripta math. (2013) 142: 257. doi:10.1007/s00229-013-0610-5

External links

• Toroidal embedding