# Integral Gassman equivalence of algebraic and hyperbolic manifolds

## TL;DR

This paper constructs large families of algebraic and hyperbolic manifolds that share many invariants, demonstrating deep connections and non-uniqueness in their geometric and algebraic structures.

## Contribution

It introduces an integral refinement of the Gassman--Sunada construction, enabling the creation of diverse manifolds with identical invariants, and addresses questions about motives and Grothendieck groups.

## Key findings

- Existence of large families of manifolds with shared invariants
- Construction of non-isometric covers that are strongly isospectral
- Non-injectivity of the map from varieties to Chow motives

## Abstract

In this paper we construct arbitrarily large families of smooth projective varieties and closed Riemannian manifolds that share many algebraic and analytic invariants. For instance, every non-arithmetic, closed hyperbolic $3$--manifold admits arbitrarily large collections of non-isometric finite covers which are strongly isospectral, length isospectral, and have isomorphic integral cohomology where the isomorphisms commute with restriction and co-restriction. We can also construct arbitrarily large collections of pairwise non-isomorphic smooth projective surfaces where these isomorphisms in cohomology are natural with respect to Hodge structure or as Galois modules. In particular, the projective varieties have isomorphic Picard and Albanese varieties, and they also have isomorphic effective Chow motives. Our construction employs an integral refinement of the Gassman--Sunada construction that has recently been utilized by D. Prasad. One application of our work shows the non-injectivity of the map from the Grothendieck group of varieties over $\overline{\mathbf{Q}}$ to the Grothendieck group of the category of effective Chow motives. We also answer a question of D. Prasad.