The phase-transition conjecture for minima of σ\sigma-Brjuno functions

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Let Bσ:[0,1]RB_\sigma:[0,1]\to\mathbb R be the σ\sigma-Brjuno function, and let ηn=(n2+4n)/2\eta_n=(\sqrt{n^2+4}-n)/2 be the nn-th fixed point of the Gauss map. For each nNn\in\mathbb N, consider the minimum of BσB_\sigma on [0,1][0,1]. Phase-transition conjecture. For all nNn\in\mathbb N, there exists a value σn(n1,n)\sigma_n^*\in(n-1,n) such that

minx[0,1]Bσ(x)={Bσ(ηn)if σ[n1,σn)Bσ(ηn+1)if σ[σn,n].\min_{x\in[0,1]}B_\sigma(x)= \begin{cases} B_\sigma(\eta_n)&\text{if }\sigma\in[n-1,\sigma_n^*)\\ B_\sigma(\eta_{n+1})&\text{if }\sigma\in[\sigma_n^*,n]. \end{cases}

Numerical evidence suggests that the minimizer remains locked at successive fixed points of the Gauss map and jumps between them at the critical thresholds σn\sigma_n^*; proving this description and the existence of these thresholds remains open.

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Primary source

Ayreena Bakhtawar, Carlo Carminati and Stefano Marmi, “On the minimum of σ-Brjuno functions”, arXiv:2603.08378 (2026).

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