Beraha's conjecture on chromatic roots near the Beraha numbers

From papers

For each integer r2r\geq2, define the Beraha number

br=2+2cos2πr.b_r=2+2\cos\frac{2\pi}{r}.

A plane triangulation is a loopless plane graph whose faces all have size three. Beraha's conjecture. For every r2r\geq2 and every ϵ>0\epsilon>0, there exists a plane triangulation with a real chromatic root in

(brϵ,br+ϵ).(b_r-\epsilon,b_r+\epsilon).

This would imply the existence of plane triangulations with real chromatic roots arbitrarily close to 44, since brb_r tends to 44. The source says that this remains open, while complex roots arbitrarily close to 44 are known.

Progress summary

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Sources & referencesView supporting material

Primary source

Bill Jackson, “Zeros of Chromatic and Flow Polynomials of Graphs”, arXiv:math/0205047 (2002).

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