Woodall's conjectures on chromatic roots of highly connected plane triangulations

From papers

A plane triangulation is a loopless plane graph in which every face has size three. Let P(G,t)P(G,t) be its chromatic polynomial, let τ=(1+5)/2\tau=(1+\sqrt{5})/2 be the golden ratio, and let θ2.61819\theta\approx2.61819 be the chromatic root of the icosahedron in (2,3)(2,3). Woodall's conjectures.

  1. If GG is 4-connected, then P(G,t)P(G,t) has at most one zero in (2,τ2)(2,\tau^2).
  2. If GG is 5-connected, then P(G,t)P(G,t) has exactly one zero in (2,θ)(2,\theta) and no zeros in (θ,3)(\theta,3).

These conjectures seek extensions of the known zero-distribution theorem for 3-connected plane triangulations. The source also gives a related finiteness conjecture: for every ϵ>0\epsilon>0, only finitely many 4-connected plane triangulations have a chromatic root in (2,τ2ϵ)(2,\tau^2-\epsilon), and only finitely many 5-connected ones have a root in (τ2+ϵ,3)(\tau^2+\epsilon,3).

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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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