Rank-2 wobbly bundles from special divisors on spectral curves

Abstract: Let $X$ be a compact connected Riemann surface of genus $g \geq 3$ and $S \rightarrow X$ a $2:1$ branched covering defined by a generic quadratic differential on $X$. In the following notes, we explore how taking direct images of line bundles defined by certain distinguished special divisors on $S$ gives rank-2 bundles having nilpotent Higgs fields on $X$. The key ingredient is the notion of Baker-Akhiezer divisors associated to Higgs bundles and choices of subbundles of the underlying rank-2 bundles.