Proof of the zig-zag conjecture

A long-standing conjecture in quantum field theory due to Broadhurst and Kreimer states that the amplitudes of the zig-zag graphs are a certain explicit rational multiple of the odd values of the Riemann zeta function. In this paper we prove this conjecture by constructing a certain family of single-valued multiple polylogarithms. The zig-zag graphs therefore provide the only infinite family of primitive graphs in ${\varphi }_4^4$ theory (in fact, in any renormalisable quantum field theory in four dimensions) whose amplitudes are now known.