Limit-profile conjecture for the strictly biased random transposition shuffle

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Let PP be the transition matrix of the biased random transposition shuffle on NN cards, let UU be the uniform distribution on permutations, let dTV⁡d_{\operatorname{TV}} denote total variation distance, and let Poiss⁡(λ)\operatorname{Poiss}(\lambda) denote the Poisson distribution with mean λ\lambda. For c∈Rc \in \mathbb{R} and b<1b<1, consider the shuffle after 12bN(log⁡N−c)\frac{1}{2b}N(\log N-c) steps. Limit-profile conjecture. The total variation distance satisfies

dTV⁡(P12bN(log⁡N−c),U)→dTV⁡(Poiss⁡(1+ec2),Poiss⁡(1)),as N→∞.d_{\operatorname{TV}}\left(P^{\frac{1}{2b}N(\log N-c)},U\right)\to d_{\operatorname{TV}}\left(\operatorname{Poiss}\left(1+\frac{e^c}{2}\right),\operatorname{Poiss}(1)\right),\qquad\text{as }N\to\infty.

This conjectures a cutoff limit profile for the strictly biased random transposition shuffle, based on the limiting distribution of the number of fixed cards. It contrasts with the unbiased random-transposition case, where the corresponding limiting Poisson mean is 1+ec1+e^c; the claimed profile remains unproved in the source.

References

Primary source

Evita Nestoridi and Alan Yan, “Cutoff for the Biased Random Transposition Shuffle”, arXiv:2409.16387 (2024).

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