Exponential decay conjecture for the crosscap-number defect

For a prime alternating knot or link KK, let γ(K)\gamma(K) denote its crosscap number and let Γ(K)\Gamma(K) denote its unoriented genus. Among all prime alternating knots, let εK(c)\varepsilon_K(c) be the proportion with γ(K)>Γ(K)\gamma(K)>\Gamma(K) at crossing number cc; similarly, let εL(c)\varepsilon_L(c) be this proportion among prime alternating links.

Exponential decay conjecture. Both proportions exponentially decay with respect to crossing number:

εK(c)ecλKandεL(c)ecλL,\varepsilon_K(c) \propto e^{-c\lambda_K} \qquad\text{and}\qquad \varepsilon_L(c) \propto e^{-c\lambda_L},

for positive constants λK\lambda_K and λL\lambda_L. In particular, both proportions approach zero as the crossing number tends to infinity.

The conjecture is motivated by log-linear plots of the observed proportions and remains open.

Sources & referencesView supporting material

Primary source

Isaias Bahena, Thomas Kindred and Jason Parsley, “Crosscap numbers of alternating links via state codes”, arXiv:2512.09887 (2025).

Additional references

6 papers in this index state this conjecture (2011–2025). The statement above is taken from the most recent of them; the others are arXiv:2302.13044, arXiv:2206.13579, arXiv:1711.10917, arXiv:1301.0811, arXiv:1109.4700.

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