Isospin violation in charged pion-kaon scattering

l We evaluate the isospin breaking corrections to the scattering amplitude pi(-)K(+) --> pi(-)K(+) at threshold in the framework of chiral perturbation theory. This channel is of particular interest for the strong 2S-2P energy level shift in pion-kaon bound states, While a prediction of this level shift is hampered by a large uncertainty in the isoscalar scattering length, we find only a moderate uncertainty of about 3% in the electromagnetic corrections which are relevant for the extraction of the scattering lengths from experiment. (C) 2002 Elsevier Science B.V. All rights reserved