The ABC model is a simple diffusive one-dimensional non-equilibrium system which exhibits a phase transition. Here we show that the cumulants of the currents of particles through the system become singular near the phase transition. At the transition, they exhibit an anomalous dependence on the system size (an anomalous Fourier's law). An effective theory for the dynamics of the single mode which becomes unstable at the transition allows one to predict this anomalous scaling. 05.70 Ln, A lot of work has been devoted recently to the study of the fluctuations of the current of heat or of particles through nonequilibrium one dimensional systems [1][2][3][4][5][6][7][8][9][10][11][12]. In such studies the basic quantity one considers is the total flux Q(t) of energy or of particles through a section of the system during time t. In the steady state this flux Q(t) fluctuates due to the randomness of the initial condition for purely deterministic models and due to the noisy dynamics in stochastic models (here we only discuss classical systems: see [13][14][15][16] for the quantum case). If one assumes that the total energy or the total number of particles in the system remains bounded, the average current lim t→∞ Q(t) t as well as the higher cumulants lim t→∞ Q(t) n c t of the flux Q(t) do not depend on the section of the system where this flux is measured.For a one dimensional system of length L, a central question is the size dependence of these cumulants [17]. In particular one would like to know whether a given system satisfies Fourier's law, meaning that, for large L, the average current scales like 1/L:where the prefactor A 1 depends on the temperatures T 1 and T 2 of the two heat baths or on the chemical potentials µ 1 and µ 2 of the two reservoirs of particles at the ends of the system. At equilibrium (T 1 = T 2 or µ 1 = µ 2 ) the prefactor A 1 in (1) vanishes but the question of the validity of Fourier's law remains. One then wants to know whether the second cumulant of Q(t) scales like 1/L.One can show that (2) holds for diffusive systems such as the SSEP (symmetric simple exclusion process) [1,4,18,19] or the KMP (Kipnis-Marchioro-Presutti) model [20]. The macroscopic fluctuation theory developed by Bertini et al. [2,21,22] allows one also to determine[1] all the cumulants of the flux Q(t), with the result that they all scale with system size as 1/L.Even corrections of order 1/L 2 have been computed in some cases [6,7].For mechanical systems with deterministic dynamics, in particular systems which conserve momentum, the average current scales as a non-integer power of the system size:The exponent α takes the value 1/2 for some exactly soluble special models [3]. Values ranging from 0.25 to 0.4 have also been reported in simulations depending on the model considered [23][24][25][26][27]. Theoretical predictions based on a mode coupling approach [28,29] or on renormalization group calculations [30] confirm this anomalous Fourier's law. Less is known on the size dependence of the higher cumulants, which are nu...