  The electronic properties of the novel two dimensional (2D) material silicene
are strongly influenced by the application of a perpendicular electric field
$E_z$ and of an exchange field $M$ due to adatoms positioned on the surface or
a ferromagnetic substrate. Within the random phase approximation, we
investigate how electron-electron interactions are affected by these fields and
present analytical and numerical results for the dispersion of plasmons, their
lifetime, and their oscillator strength. We find that the combination of the
fields $E_z$ and $M$ brings a spin and valley texture to the particle-hole
excitation spectrum and allows the formation of spin- and valley-polarized
plasmons. When the Fermi level lies in the gap of one spin in one valley, the
intraband region of the corresponding spectrum disappears. For zero $E_z$ and
finite $M$ the spin symmetry is broken and spin polarization is possible. The
lifetime and oscillator strength of the plasmons are shown to depend strongly
on the number of spin and valley type electrons that form the electron-hole
pairs.
