Positron annihilation and electron correlations in metals

The annihilation rate of positrons in metals can be related to the correlated electron wave function at the positron site. It is argued that the effective interaction at short distance for a positron in an electron gas should be dominated by terms involving one and two electrons. The positron-electron wave function is thus calculated using an effective interaction which includes the strong screening effects from one highly correlated screening electron. The electron wave functions are approximately antisymmetrized using the analogy of a recoilless impurity. The positron annihilation rates calculated using this wave function are in good agreement with the observed rates over the whole range of electron densities found in alkali metals. (auth)