40 research outputs found
A Note on Pseudo-reflections
In this note, we show that if V is a finite dimensional vector space equipped with a non-degenerate bilinear form, and one has a set of pseudo-reflections on V, preserving the form and having no non-zero common fixed vector, then the group G generated by this set is ‘sufficiently large’ in the sense that for every linear transformation T : V → V, there exists an element g ∈ G such that g − G is invertible
Dimensions of group schemes of automorphisms of truncated Barsotti--Tate groups
Let be a -divisible group over an algebraically closed field of
characteristic . Let be the smallest non-negative integer such that
is determined by within the class of -divisible groups over
of the same codimension and dimension as . We study , lifts
of to truncated Barsotti--Tate groups of level over , and the
numbers . We show that ,
is a decreasing sequence in , for we have , and for
there exists an infinite set of truncated Barsotti--Tate
groups of level which are pairwise non-isomorphic and lift .
Different generalizations to -divisible groups with a smooth integral group
scheme in the crystalline context are also proved.Comment: 52 pages. Final version as close to the galley proofs as possible. To
appear in IMR