On isospin-breaking corrections to the energy level displacement of the ground state of kaonic hydrogen

In the model of low-energy K N interactions near threshold (Ivanov A N et al 2004 Eur. Phys. J. A 21 11 (Preprint nucl-th/0310081), Ivanov A N et al 2005 Eur. Phys. J. A 23 79 (Preprint nucl-th/0406053)), we calculate isospin-breaking corrections to the energy level displacement of the ground state of kaonic hydrogen, investigated by MeiBner, Raha and Rusetsky (2004 Eur. Phys. ./. C 35 349 (Preprint hep-ph/0402261)) within the non-relativistic effective Lagrangian approach based on ChPT by Gasser and Leutwyler. Our results agree well with those by MeiBner et al. In addition we calculate the dispersive corrections, caused by the transition K - p → K 0 n → K - p with the K 0 n pair on-mass shell. We show also how hypothesis on the dominant role of the k 0 n-cusp for the S-wave amplitude of low-energy K - p scattering near threshold, used by MeiBner et al, can be realized in our approach. The result agrees fully with that of MeiBner et al.