Rational singularity

(Redirected from Rational singularities)

In mathematics, more particularly in the field of algebraic geometry, a scheme has rational singularities, if it is normal, of finite type over a field of characteristic zero, and there exists a proper birational map

from a regular scheme such that the higher direct images of applied to are trivial. That is,

for .

If there is one such resolution, then it follows that all resolutions share this property, since any two resolutions of singularities can be dominated by a third.

For surfaces, rational singularities were defined by (Artin 1966).

Formulations

edit

Alternately, one can say that   has rational singularities if and only if the natural map in the derived category

 

is a quasi-isomorphism. Notice that this includes the statement that   and hence the assumption that   is normal.

There are related notions in positive and mixed characteristic of

and

Rational singularities are in particular Cohen-Macaulay, normal and Du Bois. They need not be Gorenstein or even Q-Gorenstein.

Log terminal singularities are rational.[1]

Examples

edit

An example of a rational singularity is the singular point of the quadric cone

 

Artin[2] showed that the rational double points of algebraic surfaces are the Du Val singularities.

See also

edit

References

edit
  1. ^ (Kollár & Mori 1998, Theorem 5.22.)
  2. ^ (Artin 1966)
  • Artin, Michael (1966), "On isolated rational singularities of surfaces", American Journal of Mathematics, 88 (1), The Johns Hopkins University Press: 129–136, doi:10.2307/2373050, ISSN 0002-9327, JSTOR 2373050, MR 0199191
  • Kollár, János; Mori, Shigefumi (1998), Birational geometry of algebraic varieties, Cambridge Tracts in Mathematics, vol. 134, Cambridge University Press, doi:10.1017/CBO9780511662560, ISBN 978-0-521-63277-5, MR 1658959
  • Lipman, Joseph (1969), "Rational singularities, with applications to algebraic surfaces and unique factorization", Publications Mathématiques de l'IHÉS (36): 195–279, ISSN 1618-1913, MR 0276239