The conformal limit and projective structures

The non-abelian Hodge correspondence maps a polystable $\mathrm{S}\mathrm{L}(2,\mathbb{R})$-Higgs bundle on a compact Riemann surface $X$ of genus $g\ge 2$ to a connection which, in some cases, is the holonomy of a branched hyperbolic structure. On the other hand, Gaiotto’s conformal limit maps the same bundle to a partial oper, i.e., to a connection whose holonomy is that of a branched complex projective structure compatible with $X$. In this article, we show how these are both instances of the same phenomenon: the family of connections appearing in the conformal limit can be understood as a family of complex projective structures, deforming the hyperbolic ones into the ones compatible with $X$. We also show that, when the Higgs bundle has zero Toledo invariant, this deformation is optimal, inducing a geodesic on Teichmüller’s metric space.