The long-ranged elastic model, which is believed to describe the evolution of a self-affine rough crack-front, is analyzed to linear and non-linear orders. It is shown that the nonlinear terms, while important in changing the front dynamics, are not changing the scaling exponent which characterizes the roughness of the front. The scaling exponent thus predicted by the model is much smaller than the one observed experimentally. The inevitable conclusion is that the gap between the results of experiments and the model that is supposed to describe them is too large, and some new physics has to be invoked for another model.The self-affine roughness of a crack-front propagating under a tensile load in a randomly heterogeneous system is a well studied issue, both experimentally and theoretically. Experimentally one measures the position h(x, t) of the crack front, where h is the position of the front as a function of the span-wise coordinate x at time t, and finds that this is a self-affine function whose roughness is characterized by a scaling exponent ζ (defined below in Eq. (4)) in the range of 0.5-0.65 [1,2]. Theoretically there appears to be a consensus that the appropriate model for such dynamical roughening is a long-ranged elastic string close to its depinning threshold. This model is defined by the equation of motion for a front h(x, t), which is allowed to move only forward due to the irreversibility of the fracture process [3] ∂h(x, t) ∂tHere and bellow the integral is meant in the Cauchy Principal Value sense. The RHS of Eq. (1) is the difference between the local driving force (below referred to as G, related physically to the energy release rate driving the crack [4]), and Γ(x, h) which is a random quenched noise (representing the random material fracture energy [4]). G (0) is the control parameter that represents the energy release rate of a straight front. The integral term stands for the long ranged restoring forces stemming from bulk elastic degrees of freedom. The correspondence between the theoretical model and the experimental findings remained however unclear, since the best numerical studies of the resulting self-affine graph h(x) of this model came up with a roughness exponent ζ = 0.388 ± 0.002 [5], clearly outside the range of error of the experimental measurements. This apparent difficulty led to a number of interesting studies, insisting that the model is basically right, and that the result concerning the scaling exponent is not final. Thus, for example, in [6] the authors analyzed Eq.(1) using a functional renormalization group. They have calculated the scaling exponent ζ to one-and two-loop orders in ǫ, where ǫ = 2 − d. To one-loop order the result is ζ = ǫ/3, predicting ζ = 1/3 at d = 1, deviating considerably from the best numerical estimate.To two-loop order the prediction increases to about 0.466, leading to a statement that the model probably describes properly the experimental findings. Unfortunately, it is well known that the ǫ expansion is often an asymptotic series [7], sometime ...