Hard Lefschetz actions in Riemannian geometry with special holonomy

Naichung Conan Leung, Changzheng Li

It is known that the hard Lefschetz action, together with Kähler identities for Kähler (resp. hyperkähler) manifolds, determines a $\mathfrak{su}(1,1{)}_{sup}$ (resp. $\mathfrak{sp}(…