Essential dimension: Difference between revisions
(Created page with "{{todo|add standard macros to mathjax config file}} Define essential dimension as follows. The essential dimension of an (algebraic) stack $\X$ is the smallest dimension of a sc...") |
mNo edit summary |
||
Line 1: | Line 1: | ||
Define essential dimension as follows. The essential dimension of an (algebraic) stack $\X$ is the smallest dimension of a scheme $X$ with the following property: there is a morphism $X\to \X$ so that for any field $k$, any map $Spec(k)\to \X$, factors through $X$. Note that this agrees with the usual notion of essential dimension (?) by considering the generic point of $X$. In particular, if $Y\to \X$ is any morphism from a scheme, we have that the map from the generic point of $Y$ factors through $X$, so (with appropriate finite presentation hypotheses), there is a dense open of $Y$ where the map to $\X$ factors through $X$. | Define essential dimension as follows. The essential dimension of an (algebraic) stack $\X$ is the smallest dimension of a scheme $X$ with the following property: there is a morphism $X\to \X$ so that for any field $k$, any map $Spec(k)\to \X$, factors through $X$. Note that this agrees with the usual notion of essential dimension (?) by considering the generic point of $X$. In particular, if $Y\to \X$ is any morphism from a scheme, we have that the map from the generic point of $Y$ factors through $X$, so (with appropriate finite presentation hypotheses), there is a dense open of $Y$ where the map to $\X$ factors through $X$. | ||
[[Category:Note]] | [[Category:Note]] |
Latest revision as of 10:58, 30 November 2011
Define essential dimension as follows. The essential dimension of an (algebraic) stack $\X$ is the smallest dimension of a scheme $X$ with the following property: there is a morphism $X\to \X$ so that for any field $k$, any map $Spec(k)\to \X$, factors through $X$. Note that this agrees with the usual notion of essential dimension (?) by considering the generic point of $X$. In particular, if $Y\to \X$ is any morphism from a scheme, we have that the map from the generic point of $Y$ factors through $X$, so (with appropriate finite presentation hypotheses), there is a dense open of $Y$ where the map to $\X$ factors through $X$.