Global fixed point in low-dimensional surface group deformation space

Abstract

Under the natural action of the pure mapping class group of a surface of genus at least three, we show that any global fixed point in the low-dimensional deformation space of the surface group corresponds to the trivial representation. A key observation is that such a global fixed point gives rise to a linear representation of the pure mapping class group of the corresponding surface with a marked point. Our argument works directly on the deformation space, without assuming the semisimplicity of representations, and yields a short alternative proof of a special case of a theorem of Landesman and Litt with a slight improvement. We also discuss a possible extension of this approach from global fixed points to finite orbits of the mapping class group action.