The phase-transition conjecture for the marginal of a random contingency table

From papers

Let B,C>0B,C>0, let 0<δ<10<\delta<1, and let X=(Xij)X=(X_{ij}) be sampled uniformly from Mn,δ(B,C)\mathcal M_{n,\delta}(B,C). Let BcB_c denote the critical value. Phase-transition conjecture. There is a phase transition in δ\delta for the limiting distribution of X11X_{11} in the supercritical regime B>BcB>B_c: for 1/2<δ<11/2<\delta<1, nδ1X11n^{\delta-1}X_{11} converges in distribution to a geometric random variable, whereas for 0<δ<1/20<\delta<1/2 the marginal has the normal scaling stated below. In the thin-bezel regime, the precise conjecture is

X11C(BBc)n1δn(1δ)/2BcC+(BcC)2N(0,1).\frac{X_{11}-C(B-B_c)n^{1-\delta}}{n^{(1-\delta)/2}\sqrt{B_cC+(B_cC)^2}}\Longrightarrow\mathcal N(0,1).

The thick-bezel geometric limit is proved in the paper, while the thin-bezel normal limit and the phase transition at δ=1/2\delta=1/2 remain open.

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Primary source

Sam Dittmer, Hanbaek Lyu and Igor Pak, “Phase transition in random contingency tables with non-uniform margins”, arXiv:1903.08743 (2020).

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