  We derive from first principles the existence of a low-frequency plasmon in a
strongly coupled three-dimensional homogeneous electron gas (HEG). From its
dispersion and its satisfaction of the 3rd frequency sum rule we identify it
with the conjectured magnetic excitation in the HEG. This excitation, is
maintained by the out-of-phase oscillations of the spin-up and spin-down
densities of the electron liquid, but governed solely by the Coulomb
interaction between the particles. The frequency square of this mode is
proportional to the overlap ($r=0$) (absolute) value of the spin-up/spin-down
correlation function, and thus slightly affected by, but not contingent upon
the degree of polarization of the electron liquid. We estimate the spectral
weight of the mode: it is expected to be governed by electron-electron
collision induced spin drag. The spectral weight is manifest in the partial
spin-resolved dynamical structure functions and it is proportional to the
product of the densities of the two spin components. An independent derivation
based on a generalized Feynman Ansatz corroborates our result. The relationship
to the recently identified "spin plasmon" excitation is discussed. It is
pointed out that a scattering experiment with polarized neutrons or polarized
X-rays may be possible avenues to observe equilibrium fluctuations associated
with these modes and also to provide information on the spin drag coefficient
in the HEG.
