Fermi edge singularities: Bound states and finite-size effects

Fermi edge absorption singularities (FES) are studied using a combination of conformal field theory (CFT), an exact sum rule and numerical work on a tight-binding model which is shown to exhibit remarkable simplifying features. The relationship between FES and the Anderson orthogonality exponent is established in great generality, using CFT, including the case where the core hole potential produces a bound state. Universal results on the absorption intensity in a finite-sized sample are obtained. Various predictions are checked numerically and the evolution of the absorption intensity with electron density is studied.