Interelectronic-interaction effects on the two-photon decay rates of heavy He-like ions

Based on a rigorous quantum electrodynamics (QED) approach, a theoretical analysis is performed for the two-photon transitions in heavy He-like ions. Special attention is paid to the interelectronic-interaction corrections to the decay rates that are taken into account within the two-time Green-function method. Detailed calculations are carried out for the two-photon transitions $2\hspace{0.5em}{}^1{S}_0\to 1\hspace{0.5em}{}^1{S}_0$ and $2\hspace{0.5em}{}^3{S}_1\to 1\hspace{0.5em}{}^1{S}_0$ in He-like ions within the range of nuclear numbers $Z=28$–92. The total decay rates together with the spectral distributions are given. The obtained results are compared with experimental values and previous calculations.

Figure 1

The two-photon emission diagrams in the zeroth-order approximation. The double line indicates the electron propagators in the Coulomb field of the nucleus, while the photon emission is depicted by the wavy lines with arrows.

Figure 2

Feynman diagrams representing the first-order interelectronic-interaction corrections to the two-photon emission. Notations are the same as in Fig. 1.

Figure 3

One-photon exchange diagram. The photon propagator is represented by the wavy line.

Figure 4

The counterterm diagrams for the first-order interelectronic-interaction corrections to the two-photon emission. The triple lines describe the electron propagators in the effective potential. The symbol $\otimes$ represents the extra interaction term associated with the local screening potential.

Figure 5

The counterterm diagrams for the one-photon exchange correction. Notations are the same as in Fig. 4.

Figure 6

The $2\hspace{0.5em}{}^1{S}_0$ two-photon energy distribution functions ${\mathit{dW}}_{B;A}/\mathit{dy}$, normalized to the corresponding total decay rates, plotted as a function of the reduced energy $y$ for He-like nickel, tin, europium, and uranium ions.

Figure 7

The $2\hspace{0.5em}{}^3{S}_1$ two-photon energy distribution functions ${\mathit{dW}}_{B;A}/\mathit{dy}$, normalized to the corresponding total decay rates, plotted as a function of the reduced energy $y$ for He-like nickel, tin, europium, and uranium ions.