Mixed twistor structures

Abstract

The purpose of this paper is to introduce the notion of mixed twistor structure, a generalization of the notion of mixed Hodge structure. The utility of this notion is to make possible a theory of weights for various things surrounding arbitrary representations of the fundamental group of a smooth projective variety. We give some examples of generalizations of classical results for variations of mixed Hodge structure, to the twistor setting. This supports a ``meta-theorem'' (which we state but don't prove) that one can everywhere replace the word ``Hodge'' by the word ``twistor''. We show that the jet spaces of hyperk\"ahler or more generally hypercomplex manifolds have natural mixed twistor structures which determine the hypercomplex structure in a formal neighborhood of a point.