Adiabatic stability under semi-strong interactions: The weakly damped regime Thomas BellskyArjen DoelmanTasso KaperKeith Promislow 35B2535K4535K57Reaction-diffusion systemsemi-strong interactionrenormalization groupnonlocal eigenvalue problem (NLEP)normal hyperbolicity We rigorously derive multi-pulse interaction laws for the semi-strong interactions in a family of singularly-perturbed and weakly-damped reaction-diffusion systems in one space dimension. Most significantly, we show the existence of a manifold of quasi-steady $N$-pulse solutions and identify a "normal-hyperbolicity" condition which balances the asymptotic weakness of the linear damping against the algebraic evolution rate of the multi-pulses. Our main result is the adiabatic stability of the manifolds subject to this normal hyperbolicity condition. More specifically, the spectrum of the linearization about a fixed $N$-pulse configuration contains an essential spectrum that is asymptotically close to the origin, as well as {\em semi-strong} eigenvalues which move at leading order as the pulse positions evolve. We characterize the semi-strong eigenvalues in terms of the spectrum of an explicit $N\times N$ matrix, and rigorously bound the error between the $N$-pulse manifold and the evolution of the full system, in a polynomially weighted space, so long as the semi-strong spectrum remains strictly in the left-half complex plane, and the essential spectrum is not too close to the origin. Indiana University Mathematics Journal 2013 text pdf 10.1512/iumj.2013.62.5159 10.1512/iumj.2013.62.5159 en Indiana Univ. Math. J. 62 (2013) 1809 - 1859 state-of-the-art mathematics http://iumj.org/access/