Energy and decay width of the πK atom

The energy and the decay width of the πK atom are evaluated in the framework of the quasipotential-constraint theory approach. The main electromagnetic and isospin symmetry breaking corrections to the lowest-order formulas for the energy shift from the Coulomb binding energy and for the decay width are calculated. They are estimated to be of the order of a few per cent. We display formulas to extract the strong interaction S-wave πK scattering lengths from future experimental data concerning the πK atom. (orig.)