Conjecture on universal rational-function limits of cluster-expansion terms

Let AA be sampled from the ensemble of n×nn\times n zero-one matrices with every row and column sum equal to rr, and let EE denote expectation in this ensemble. Let E1E_1 and E2E_2 be the two approximating expectations defined in the paper, and let Ti(n)T_i(n) be the corresponding cluster-expansion terms. Define

h(i)={i/2,if i is even,(i+1)/2,if i is odd.h(i)=\begin{cases}i/2,&\text{if }i\text{ is even},\\(i+1)/2,&\text{if }i\text{ is odd}. \end{cases}

Universal-limit conjecture. The limits obtained using E1E_1, E2E_2, or EE are equal, and

limn1nTi(n)Qi=kak(i)rk,\lim_{n\to\infty}\frac{1}{n}T_i(n)\equiv Q_i=\sum_k\frac{a_k(i)}{r^k},

with i1kh(i)i-1\geq k\geq h(i). The claim refines the preceding existence conjecture by prescribing the dependence on rr. The paper gives computed examples for Q2Q_2 through Q7Q_7 but no proof or resolution.

Sources & referencesView supporting material

Primary source

Paul Federbush, “A Mysterious Cluster Expansion Associated to the Expectation Value of the Permanent of 0-1 Matrices”, arXiv:1607.00885 (2023).

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