Antiprotonic atoms with nonperturbative inclusion of vacuum polarization and finite nuclear mass
We demonstrate that energy levels of excited states in a hydrogenic system consisting of an arbitrary nucleus and an antiproton can be calculated within the framework of nonrelativistic quantum electrodynamics, even for a large nuclear charge $Z$. It is because for rotational states the expansion parameter is $Z\,\alpha/n$. The main advantage of this approach is the possibility of exact inclusion of the finite nuclear mass, which we achieve up to the $(Z\,\alpha)^6$ order. In addition, we include unperturbatively the one-loop and two-loop electron vacuum polarization (evp) potentials in the nonrelativistic Hamiltonian, as well as in the leading relativistic correction. The obtained results for $l>1$ states of antiprotonic atoms with spinless nucleus are the most accurate to date. We make available a user-friendly {\sl Mathematica} code for antiprotonic atoms {\sl PbarSpectr}, which can be further improved by combining evp potentials with $(Z\,\alpha)^5$ QED effects, by adding three-loop evp, and by extending to an arbitrary nuclear spin. Finally, we note that rotational states of antiprotonic atoms can be used to determine the mean square nuclear charge radius much more accurately than from electronic or muonic atoms.