Towards Landau-Ginzburg models for cominuscule spaces via the exceptional cominuscule family

We present projective Landau-Ginzburg models for the exceptional cominuscule homogeneous spaces $\mathbb{OP}^2 = E_6^\mathrm{sc}/P_6$ and $E_7^\mathrm{sc}/P_7$, known respectively as the Cayley plane and the Freudenthal variety. These models are defined on the complement $X^\vee_\mathrm{can}$ of an anti-canonical divisor of the "Langlands dual homogeneous spaces" $\mathbb{X}^\vee = P^\vee\backslash G^\vee$ in terms of generalized Pl\"ucker coordinates, analogous to the canonical models defined for Grassmannians, quadrics and Lagrangian Grassmannians in arXiv:1307.1085, arXiv:1404.4844, arXiv:1304.4958. We prove that these models for the exceptional family are isomorphic to the Lie-theoretic mirror models defined in arXiv:math/0511124 using a restriction to an algebraic torus, also known as the Lusztig torus, as proven in arXiv:1912.09122. We also give a cluster structure on $\mathbb{C}[\mathbb{X}^\vee]$, prove that the Pl\"ucker coordinates form a Khovanskii basis for a valuation defined using the Lusztig torus, and compute the Newton-Okounkov body associated to this valuation. Although we present our methods for the exceptional types, they generalize immediately to the members of other cominuscule families.Comment: 45 pages, 2 figures, code available at https://github.com/foxflo/ExceptionalCominusculeSpace