We study the phason propagator and the electric conductivity of spin d
ensity waves (SDW) in the presence of long range Coulomb interaction.
We find that in the longitudinal limit, the phason propagator is stron
gly modified, while in the transverse limit, the Coulomb effect disapp
ears completely. Further in the longitudinal limit, the plasmon exhaus
ts the optical sum rule independent of whether the system is in the no
rmal state or in SDW. However, in the transverse limit, the plasmon co
ntribution drops out completely from the conductivity. On the other ha
nd, the polariton will give rise to a peculiar structure in the low fr
equency absorption.