regular element of a Lie algebra
An element of a Lie algebra is called regular if the dimension of its centralizer is minimal among all centralizers of elements in .
Regular elements clearly exist and moreover they are Zariski dense in . The function is an upper semi-continuous function . Indeed, it is a constant minus and is lower semi-continuous. Thus the set of elements whose centralizer dimension is (greater than or) equal to that of any given regular element is Zariski open and non-empty.
If is reductive then the minimal centralizer dimension is equal to the rank of .
More generally if is a representation for a Lie algebra , an element is called regular if the dimension of its stabilizer is minimal among all stabilizers of elements in .
Examples
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1.
In a diagonal matrix is regular iff for all pairs . Any conjugate of such a matrix is also obviously regular.
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2.
In the nilpotent matrix
is regular. Moreover, it’s adjoint orbit contains the set of all regular nilpotent elements. The centralizer of this matrix is the full subalgebra of trace zero, diagonal matricies.
Title | regular element of a Lie algebra |
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Canonical name | RegularElementOfALieAlgebra |
Date of creation | 2013-03-22 15:30:53 |
Last modified on | 2013-03-22 15:30:53 |
Owner | benjaminfjones (879) |
Last modified by | benjaminfjones (879) |
Numerical id | 6 |
Author | benjaminfjones (879) |
Entry type | Definition |
Classification | msc 17B05 |
Defines | regular element |