broadcast in Room 515, Cosmology Bldg., NTU, Online seminar
(線上演講 於台大次震宇宙館515教室直播/收播)
Lifting from an Ample Section The Case of Weighted Blow-ups
Marco Andreatta (Università di Torino)
Abstract:
A classical method to study a projective variety is to consider its hyperplane section and "lift" the properties of the section to the variety. This is sometimes called Apollonius method and it works well since in general a variety is at least as special as any of its hyperplane sections. For example a weighted projective space can be an hyperplane section only of a weighted projective space (S. Mori 1975).
We extend this result in a "relative situation", namely we consider
to be a local, projective, divisorial contraction between normal varieties of dimension
with
-factorial singularities and
to be a
-ample Cartier divisor. If
has a structure of a weighted blow-up then
, as well, has a structure of weighted blow-up.
As an application we consider a local projective contraction
from a variety
with terminal
-factorial singularities, which contracts a prime divisor
to an isolated
-factorial singularity
, such that \\
is
-ample, for a
-ample Cartier divisor
on
.
Using the above result, the existence of a "good" general section of
and the existing results in dimension
, we prove that
is a hyperquotient singularity and
is a weighted blow-up.
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