SINGULAR BEHAVIOR OF ELECTRONS AND OF COMPOSITE FERMIONS IN A FINITE EFFECTIVE-FIELD

We calculate the self-energy Sigma(n)(epsilon) of fermions in Landau l evel n, in a finite field. Two cases are considered, in which fermions couple either to gauge fluctuations (as in the composite fermion gaug e theory) or to phonons, as an example of a Fermi liquid. Perturbative calculations of the composite fermion spectrum show an unphysical sup pression of the quasiparticle spectral weight at the composite fermion levels. We argue that this problem might be resolved by a non-perturb ative calculation; alternatively, the system might be unstable.