LibreTimes

Sean Cotner

@sean_cotner

NSF Research Fellow and Postdoc at the University of Bonn

1 follower15 works
About
NSF Research Fellow and postdoc at the University of Bonn. Previously an NSF Research Fellow and Postdoctoral Assistant Professor at the University of Michigan, and before that a graduate student at Stanford, advised by Brian Conrad. Interested in arithmetic geometry, algebraic groups (broadly construed), and integral questions connected to the local Langlands program.
Personal Information

Current Positions

NSF Research Fellow and Postdoc, University of Bonn

Researcher Info
Most popular works
All works

The Steinberg Representation

Aug 24, 2026TheorySean Cotner

Description:

An introduction to the Steinberg representation of a finite group of Lie type — its alternating-sum construction from parabolic inductions, worked out explicitly for SL_2.

0
390

Some examples of algebraic groups

Aug 24, 2026TheorySean Cotner

Description:

Two pathological phenomena for algebraic groups over general bases — a group degenerating between the multiplicative and additive group across a DVR, and a non-affine identity component — built as centralizers in SL_n.

0
320
Recent works

An example of a non-reduced Picard scheme

Aug 24, 2026TheorySean Cotner

Description:
An example, due to Serre, of a smooth projective surface in positive characteristic whose Picard scheme fails to be reduced, worked out via the two governing dimension inequalities.
1
280

A curiosity: “supersmooth” varieties

Aug 24, 2026TheorySean Cotner

Description:
A rigidity condition on schemes, strictly stronger than smoothness, introduced with examples and a look at where it fails to be geometric — no known application, just a curiosity.
1
220