Decorated rotation number determines smooth rigidity classes for circle diffeomorphisms with breaks

A circle diffeomorphism with breaks is a circle diffeomorphism having break points; the decorated rotation number is the rotation number together with the additional break data, and the size of a break is its associated break invariant. Let γ\gamma range over decorated rotation numbers.

Rigidity conjecture. There is a full-measure set of decorated rotation numbers γ\gamma such that, whenever T1T_1 and T2T_2 are circle diffeomorphisms with breaks having breaks of the same size and the same decorated rotation number, T1T_1 and T2T_2 are smoothly conjugate.

This conjecture concerns the characterization of smooth rigidity classes by renormalization data. In the one-break case, restricted to irrational rotation numbers, hyperbolicity of the renormalization operator and the description of rotation-number level sets as stable spaces are stated to imply the conjecture; the general statement remains open.

Sources & referencesView supporting material

Primary source

Selim Ghazouani and Konstantin Khanin, “The symplectic structure of renormalisation of circle diffeomorphisms with breaks”, arXiv:1907.07021 (2019).

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