Strong rigidity of periodic points outside equivariant torus quotients

Let FF be a field of characteristic zero and let SFS_F be a normal affine surface over FF. Suppose that f,g}Aut(SF)f,g\rbrace\in\operatorname{Aut}(S_F) are loxodromic automorphisms. Strong rigidity conjecture. The following are equivalent:

  1. Per(f)Per(g)\operatorname{Per}(f)\cap\operatorname{Per}(g) is Zariski dense.
  2. There exist N,MZ{0}N,M\in\mathbf{Z}\setminus\{0\} such that fN=gMf^N=g^M.

This equivalence is conjectured for normal affine surfaces except when SFS_F is an equivariant quotient of Gm2\mathbb{G}_m^2, since such quotients provide counterexamples to strong rigidity of periodic points.

Sources & referencesView supporting material

Primary source

Marc Abboud, “Rigidity of periodic points for loxodromic automorphisms of affine surfaces”, arXiv:2406.11510 (2025).

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