Multiparticle perturbation theory and an accurate calculation of parity nonconservation in cesium

A method of calculating higher-order correlation corrections, using Green's functions and the Feynman diagrammatic technique, is developed. A basis of the single-electron orbitals is computed using the relativistic Hartree-Fock method. The interaction of an atom with an external field is computed by solving the time-dependent Hartree-Fock equations. In the methodology presented, we consider all the second-order correlation corrections and the dominating classes of higher order diagrams: the screening of the Coulomb interaction of electrons, particle-hole interaction and mass operator iterations. The calculation of the energy levels, the intervals of hyperfine structure and the amplitudes of the allowed EI-transitions in C_s shows that the method developed ensures precision at the 0.1–1% level. A calculation of the parity nonconservation of the El-amplitude of the transition 6s–7s in Cs is produced. The result <6s¦D_z¦7s> = –(0.91 ± 0.01)·10^–11 i¦e¦a^B (–Q_W/N) is obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 108–119, August, 1990.