title: Nonperturbative calculation of the two-loop lamb shift in Li-like ions.
abstract: A calculation valid to all orders in the nuclear-strength parameter is presented for the two-loop Lamb shift, notably for the two-loop self-energy correction, to the 2p-2s transition energies in heavy Li-like ions. The calculation removes the largest theoretical uncertainty for these transitions and yields the first experimental identification of two-loop QED effects in the region of the strong binding field.
authors.affiliation: Center for Advanced Studies, St. Petersburg State Polytechnical University, Polytekhnicheskaya 29, St. Petersburg 195251, Russia.
authors.forename: V A
authors.initials: VA
authors.lastname: Yerokhin
authors.forename: P
authors.initials: P
authors.lastname: Indelicato
authors.forename: V M
authors.initials: VM
authors.lastname: Shabaev