UPPER-BOUNDS ON PLASMON DISPERSION IN THE DEGENERATE BOSON PLASMA

Sum-rule arguments are used to derive two rigorous upper bounds for th e plasmon dispersion curve in a fluid of charged bosons at zero temper ature. They are readily evaluated (i) at long wavelengths, to show tha t the leading dispersion coefficient is negative at all couplings, and (ii) at weak coupling, to obtain a simple analytic upper bound for th e whole dispersion curve.