Dynamical degrees of affine-triangular automorphisms in dimension four

Abstract: In this paper, let k be the affine n-space over an arbitrary field k. We show that dynamical degrees of affine-triangular automorphisms in dimension 4 are algebraic integers of degree not larger than 4. As a consequence, if char(k) is not equal to 2, then dynamical degrees of quadratic automorphisms in dimension 4 are algebraic integers of degree not larger than 4. We also explore some results in higher dimensions. These results partially give the affirmative answer to the Conjecture in DF21