  In Montgomery (2009a), we show that accretion discs in binary systems could
retrogradely precess by tidal torques like the Moon and the Sun on a tilted,
spinning, non-spherical Earth. In addition, we show that the state of matter
and the geometrical shape of the celestial object could significantly affect
the precessional value. For example, a Cataclysmic Variable (CV) Dwarf Novae
(DN) non-magnetic system that shows negative superhumps in its light curve can
be described by a retrogradely precessing, differentially rotating, tilted
disc. Because the disc is a fluid and because the gas stream overflows the
tilted disc and particles can migrate into inner disc annuli, coupled to the
disc could be a retrogradely precessing inner ring that is located near the
innermost annuli of the disc. However, numerical simulations by Bisikalo et al.
(2003, 2004) and this work show that an inner spiral density wave can be
generated instead of an inner ring. Therefore, we show that retrograde
precession in non-magnetic, spinning, tilted CV DN systems can equally be
described by a retrogradely precessing and differentially rotating disc with an
attached retrogradely precessing inner spiral density wave so long as the wave
appears at the same radius as the ring and within the plane of the tilted disc.
We find that the theoretical results generated in this work agree well with the
theoretical results presented in Montgomery (2009a) and thus with the numerical
simulations and select CV DN systems in Montgomery (2009b) that may have a main
sequence secondary. Therefore, pressure effects do need to be considered in CV
DN systems that exhibit negative superhumps if the accretion discs are tilted
and have an inner spiral density wave that is in the plane of the disc.
