Is the five-flow conjecture almost false?

TL;DR

This paper disproves the conjecture that flow polynomials of certain graphs have no real roots greater than 5, by explicitly finding such roots and showing their accumulation near 5.

Contribution

It demonstrates that the modified five-flow conjecture is false by identifying infinitely many graphs with real flow roots exceeding 5 and analyzing their accumulation points.

Findings

Existence of real flow roots greater than 5 in non-planar cubic graphs.

Explicit computation of flow polynomial for G(119,7) with roots near 5.

Accumulation of real roots at Q=5 for specific graph families.

Abstract

The number of nowhere zero Z_Q flows on a graph G can be shown to be a polynomial in Q, defining the flow polynomial \Phi_G(Q). According to Tutte's five-flow conjecture, \Phi_G(5) > 0 for any bridgeless G.A conjecture by Welsh that \Phi_G(Q) has no real roots for Q \in (4,\infty) was recently disproved by Haggard, Pearce and Royle. These authors conjectured the absence of roots for Q \in [5,\infty). We study the real roots of \Phi_G(Q) for a family of non-planar cubic graphs known as generalised Petersen graphs G(m,k). We show that the modified conjecture on real flow roots is also false, by exhibiting infinitely many real flow roots Q>5 within the class G(nk,k). In particular, we compute explicitly the flow polynomial of G(119,7), showing that it has real roots at Q\approx 5.0000197675 and Q\approx 5.1653424423. We moreover prove that the graph families G(6n,6) and G(7n,7) possess real flow roots that accumulate at Q=5 as n\to\infty (in the latter case from above and below); and that Q_c(7)\approx 5.2352605291 is an accumulation point of real zeros of the flow polynomials for G(7n,7) as n\to\infty.