THE PHYSICAL SIGNIFICANCE OF SINGULARITIES IN THE CHERN-SIMONS FERMI-LIQUID DESCRIPTION OF A PARTIALLY FILLED LANDAU-LEVEL

We analyze the linear response of a half-filled Landau level to long w avelength and low-frequency driving forces, using Fermi liquid theory for composite fermions. This response is determined by the composite f ermions quasi-particle mass m and quasi-particle Landau interaction f unction f(theta-theta'). Analyzing infrared divergences of perturbatio n theory, we obtain an exact expression for m, and conjecture the for m of f(theta-theta'). We then conclude that in the limit of infinite c yclotron frequency, and small q,omega, the composite fermion excitatio n spectrum is continuous for [GRAPHICS] with gamma an unknown number. For fractional quantum Hall states near a half-filled Landau level, we derive an exact expression for the energy gap.