
Alison Parker
University of Sydney
Higher extensions for SL_{2}(k)
Friday 24th September, 12:0512:55pm,
Carslaw 175.
In this talk we review a variant of the LyndonHochschildSerre
spectral sequence for algebraic groups.
We use this to show that the E_{2} page of the spectral sequence
for the group Ext*(Delta(lambda),Delta(mu)) is the
same as the Einfinity page.
In particular we get a nice recursion formula for the Ext
group and so it may be completely calculated by this method.
Here Delta(lambda) is the Weyl module for SL_{2}(k)
of highest weight lambda, mu is another highest weight
and k is an algebraically closed field of prime
characteristic.
We get similar results for Ext*(L(lambda),Delta(mu))
and Ext*(Delta(mu),L(lambda)) where L(lambda) is the
simple module of highest weight mu.
The talk will assume some familiarity with homological algebra
but none with spectral sequences.







