Gumbel separation-profile conjecture for the random transposition shuffle

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Consider, for n≥2n\geq 2, the random transposition shuffle (Xt(n))t≥0(X_t^{(n)})_{t\geq 0} on the symmetric group Sn\mathfrak{S}_n, in discrete or continuous time, and let dsep(n)(t)\mathrm{d}_{\textup{sep}}^{(n)}(t) denote its separation distance to stationarity at time t≥0t\geq 0. For any c∈Rc\in\mathbb{R}, the Gumbel separation-profile conjecture asserts that

dsep(n)(⌊12n(ln⁡n+c)⌋)→n→∞1−e−e−c.\mathrm{d}_{\textup{sep}}^{(n)}\left(\left\lfloor \frac{1}{2}n(\ln n+c)\right\rfloor\right)\xrightarrow[n\to\infty]{}1-e^{-e^{-c}}.

In words, the separation profile for random transpositions should be given by a Gumbel distribution. The conjecture is motivated by the likelihood calculation for nn-cycles and would follow from a positive answer to the question of whether, for every time, the minimum of likelihood is attained at nn-cycles. Its resolution is not supplied here.

References

Primary source

Lucas Teyssier, “Every cutoff profile is possible”, arXiv:2509.23069 (2025).

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