The puzzle of kaonic hydrogen

We discuss the recent proposals by Law, Turner and Barrett, and by Schnick and Landau, to produce theoretically an «attractive» strong-interaction shift for the 1 s atomic K^-p level while avoiding conflict with a minimum set of {Mathematical expression} N scattering and reaction data at low energy. Arguments are presented which refute the former claim and cast serious doubts on the validity of the latter. Finally, a model-dependent finite-range correction to the Dalitz-Tuan expression is offered, a correction that amounts to less than 5% modification in the value of the level shift it yields for kaonic-hydrogen ground state, for given {Mathematical expression} N scattering lengths.