Moment maps and non-reductive geometric invariant theory

When a complex reductive group acts linearly on a projective variety, the GIT quotient can be identified with an appropriate symplectic quotient. The aim of this talk is to discuss an analogue of this description for GIT quotients by suitable non-reductive actions. In general GIT for non-reductive linear algebraic group actions is much less well behaved than for reductive actions. However when the unipotent radical U of a linear algebraic group is graded, in the sense that a Levi subgroup has a central one-parameter subgroup which acts by conjugation on U with all weights strictly positive, then GIT for a linear action of the group on a projective variety has better properties than in the general case, and (at least under some additional conditions) we can ask for moment map descriptions of the quotients.