Ponderomotive force of quasiparticles in a plasma

We derive the force exerted on the background plasma by an arbitrary distri bution of noninteracting quasiparticles, corresponding to either collective excitations of the plasma (plasmons and phonons) or dressed particles (pho tons and neutrinos). Our approach is based on the effective Hamiltonian des cribing the quasiclassical dynamics of the individual particles in the pres ence of a background medium. We recover the usual results for the relativis tic ponderomotive force of a photon gas and a plasmon gas and we derive the force, due to weak interactions, exerted by the electron neutrinos in a ba ckground medium containing electrons, positrons, and neutrons with arbitrar y distribution functions. Generalization to other background species and ot her neutrino flavors is also discussed. [S1063-651X(99)04102-1].