On the geometry of a 4-dimensional extension of a $q$-Painlevé I equation with symmetry type $A_1^{(1)}$

Abstract

We present a geometric study of a four-dimensional integrable discrete dynamical system which extends the autonomous form of a $q$-Painlevé I equation with symmetry of type $A_1^{(1)}$. By resolution of singularities it is lifted to a pseudo-automorphism of a rational variety obtained from $({\mathbb{P}}^1{)}^{\times 4}$ by blowing up along 28 subvarieties and we use this to establish its integrability in terms of conserved quantities and degree growth. We embed this rational variety into a family which admits an action of the extended affine Weyl group $\tilde{W}(A_1^{(1)})\times \tilde{W}(A_1^{(1)})$ by pseudo-isomorphisms. We use this to construct two 4-dimensional analogues of $q$-Painlevé equations, one of which is a deautonomisation of the original autonomous integrable map.

25 pages