Some fourth order CY-type operators with non symplectically rigid   monodromy
  We study tuples of matrices with rigidity index two in $\Sp_4(\mathbb{C})$, which are potentially induced by differential operators of Calabi-Yau type. The constructions of those monodromy tuples via algebraic operations and middle convolutions and the related constructions on the level differential operators lead to previously known and new examples. 
Michael Bogner and Stefan Reiter
math.AG math.CA