Transition Layer for the Heterogeneous Allen-Cahn Equation

We consider the equation (1) ε∆u = (u− a(x))(u − 1) in Ω, ∂u ∂ν = 0 on ∂Ω, where Ω is a smooth and bounded domain in R, ν the outer unit normal to ∂Ω, and a a smooth function satisfying −1 < a(x) < 1 in Ω. We set K, Ω+ and Ω− to be respectively the zero-level set of a, {a > 0} and {a < 0}. Assuming ∇a 6= 0 on K and a 6= 0 on ∂Ω, we show that there exists a sequence εj → 0 such that equation (1) has a solution uεj which converges uniformly to ±1 on the compact sets of Ω± as j → +∞. This result settles in general dimension a conjecture posed in [19], proved in [15] only for n = 2.