Screening in a System of Many Particles Composed of Two Charged Fermions Application to Excitons

A many‐particle system of composite particles consisting of two different fermions each and interacting by the Coulomb potential is considered. For the case that the composites are present in bound states only the constituent self‐energy is calculated to linear order in the densitytaking all symmetries of the many‐body wavefunctions into account. The correlational part (screening part) of the selfenergy is calculated in the Born collision approximation. Numerical values for the shift of the continuum‐edge of the spectrum of excitons in GaAs are presented.