Goulden–Rattan square-coefficient inequalities for expanders

Let Yk(u)Y_k(u) be the set of expanders with kk edges, u1u-1 white vertices and one black vertex. Let Xk(i,j)X_k(i,j) be the set of expanders with kk edges, i+j2i+j-2 white vertices and two black vertices with weights i1i-1 and j1j-1. Goulden–Rattan's square-coefficient conjecture. For natural numbers iji\neq j and any natural number kk,

(2j1)Xk(j,j)(j1)2Yk(2j)(2j-1)\left\|X_k(j,j)\right\|\geq (j-1)^2\left\|Y_k(2j)\right\|

and

(i+j1)Xk(i,j)2(i1)(j1)Yk(i+j).(i+j-1)\left\|X_k(i,j)\right\|\geq 2(i-1)(j-1)\left\|Y_k(i+j)\right\|.

These inequalities reformulate the Goulden–Rattan conjecture for square coefficients in terms of expanders. The supplied text does not state whether these inequalities have been proved or refuted, so their status remains open.

Sources & referencesView supporting material

Primary source

Mikołaj Marciniak, “Quadratic coefficients of Goulden-Rattan character polynomials”, arXiv:2104.13512 (2022).

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