The Möbius-band Gram determinant conjecture for diagrams with one crosscap curve

Let Mbn,1Mb_{n,1} be the set of crossingless-connection diagrams between 2n2n marked boundary points of the Möbius band, with exactly one curve intersecting the crosscap. Let GnMbn,1G_n^{Mb_{n,1}} be its Gram matrix, and let G~nMbn,1\tilde{G}_n^{Mb_{n,1}} be obtained by substituting y=0y=0 and w=1w=1. Let TkT_k denote the Chebyshev polynomials of the first kind. The Möbius-band one-crosscap determinant conjecture. For n2n\geq 2,

det(G~nMbn,1)=k=2n(T2k(d)2)(2nnk).\det(\tilde{G}_n^{Mb_{n,1}})=\prod_{k=2}^n\bigl(T_{2k}(d)-2\bigr)^{\binom{2n}{n-k}}.

The determinant is known to divide the Gram determinant of type (Mb)1(Mb)_1, but the displayed closed formula was presented as a conjecture.

Sources & referencesView supporting material

Primary source

Anthony Christiana, Dionne Ibarra and Gabriel Montoya-Vega, “Chebyshev polynomials and Gram determinants from the Möbius band”, arXiv:2504.16439 (2025).

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