Quantitative Stability of Two Weakly Interacting Kinks in the Stationary phi^6 Model

We study the stationary phi^6 model given by the equation -phi’'(x) + 2 phi(x) - 8 phi(x)^3 + 6 phi(x)^5 = 0 for x in R, and establish sharp quantitative stability estimates for configurations close to two weakly interacting kinks. More precisely, there exist constants a > 0 and epsilon > 0 such that, for any function u in L-infinity satisfying || u - H_{0,1}(x + x1) - H_{-1,0}(x + x2) ||{H1} < epsilon with x2 - x1 > a, there exist constants y1, y2 such that || u - H{0,1}(x + y1) - H_{-1,0}(x + y2) ||{H1} + exp(-sqrt(2) (y2 - y1)) <= C * || u’’ - 2 u + 8 u^3 - 6 u^5 ||{L2}.