Spectral interpretations of dynamical degrees and applications

Nguyen-Bac Dang; Charles Favre

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arXiv · 2006.10262

Spectral interpretations of dynamical degrees and applications

Nguyen-Bac Dang·Charles Favre

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Abstract

We prove that dynamical degrees of rational self-maps on projective varieties can be interpreted as spectral radii of naturally defined operators on suitable Banach spaces. Generalizing Shokurov's notion of b-divisors, we consider the space of b-classes of higher codimension cycles, and endow this space with various Banach norms. Building on these constructions, we design a natural extension to higher dimensions of the Picard-Manin space introduced by Cantat and Boucksom-Favre-Jonsson in the case of surfaces. We prove a version of the Hodge index theorem, and a surprising compactness result in this Banach space. We use these two theorems to infer a precise control of the sequence of degrees of iterates of a map under the assumption that the square of the first dynamical degree is strictly larger than the second dynamical degree. As a consequence, we obtain that the dynamical degrees of an automorphism of the affine 3-space are all algebraic numbers.

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Nguyen-Bac Dang, Charles Favre. 2020-06-18. Spectral interpretations of dynamical degrees and applications. https://arxiv.org/abs/2006.10262

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