Explicit cutoff profiles for colored top-$m$-to-random shuffles

Abstract

We study $p$-colored top-$m$-to-random on the wreath product $G_{n,p}=C_p\wr S_n$, with $m$ fixed. Using the Nakano-Sadahiro-Sakurai basis elements $B_m$, we obtain exact nested-set occupancy mixtures and reduce the likelihood ratio to the single statistic $L_p$. This yields exact formulas for separation and $L^{\infty }(U)$, and exact one-dimensional formulas for total variation, $L^q(U)$ ($1\le q<\infty$), $\ddot{I}{‡}^2$, and relative entropy. At $k=\lfloor \frac{n}{m}(\log n+c)\rfloor$, the number of never-chosen labels in the associated $m$-subset occupancy model converges in law to $\mathrm{Poisson}(e^{-c})$, giving the total-variation profile $f_p(c)$, the separation profile, and the corresponding $L^q(U)$, $L^{\infty }(U)$, $\ddot{I}{‡}^2$, and relative-entropy profiles. For $m=1$ we recover colored top-to-random; for $p=1$, the total-variation profile reduces to the Diaconis-Fill-Pitman profile. For the reversed chain, we also identify optimal strong stationary times whose tail probabilities are exactly the separation distances.

45 pages