Virtual homological eigenvalues and the Weil--Petersson translation length

TL;DR

This paper establishes a new inequality linking the growth of virtual homological eigenvalues with the Weil--Petersson translation length for pseudo-Anosov automorphisms, providing bounds on eigenvalue growth in relation to surface covers.

Contribution

It introduces the homological Jensen square sum and proves its linear growth bound relative to covering degree, connecting eigenvalue growth with Weil--Petersson translation length.

Findings

Homological Jensen square sum grows at most linearly with covering degree.

Square root of growth rate bounded by a constant times Weil--Petersson length.

New inequality aligns with existing bounds by Kojima, McShane, and L extsuperscript{e}.

Abstract

For any pseudo-Anosov automorphism on an orientable closed surface, an inquality is established bounding certain growth of virtual homological eigenvalues with the Weil--Petersson translation length. The new inquality fits nicely with other known inequalities due to Kojima and McShane, and due to L\^e. The new quantity to be considered is the square sum of the logarithmic radii of the homological eigenvalues (with multiplicity) outside the complex unit circle, called the homological Jensen square sum. The main theorem is as follows. For any cofinal sequence of regular finite covers of a given surface, together with lifts of a given pseudo-Anosov, the homological Jensen square sum of the lifts grows at most linearly fast compared to the covering degree, and the square root of the growth rate is at most $1/\sqrt{4\pi}$ times the Weil--Petersson translation length of the given pseudo-Anosov.