Noble-number conjecture for the local minima of the Brjuno function

Let B1B_1 denote the classical Brjuno function, let M \mathcal{M} be the set of its local minima, and let N\mathcal{N} be the set of noble numbers, namely the numbers whose regular continued fraction expansion is of the form [0;a1,a2,,an,1][0;a_1,a_2,\ldots,a_n,\overline{1}]. Local-minima conjecture.

M=N.\mathcal{M}=\mathcal{N}.

The global minimum of B1B_1 is known to be attained at the golden number, and the cited corollary gives the corresponding lower bound on (0,1/2)(0,1/2). Numerical evidence suggests that all local minima, not only these known global-minimum examples, are precisely the noble numbers.

Sources & referencesView supporting material

Primary source

Ayreena Bakhtawar, Carlo Carminati and Stefano Marmi, “Global and local minima of α-Brjuno functions”, arXiv:2401.17679 (2025).

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