  The angle between the stellar spin and the planetary orbit axes (spin-orbit
angle) is supposed to carry valuable information on the initial condition of
the planet formation and the subsequent migration history. Indeed current
observations of the Rossiter- McLaughlin effect have revealed a wide range of
spin-orbit misalignments for transiting exoplanets. We examine in detail the
tidal evolution of a simple system comprising a Sun-like star and a hot Jupiter
adopting the equilibrium tide and the inertial wave dissipation effects
simultaneously. We find that the combined tidal model works as a very efficient
realignment mechanism; it predicts three distinct states of the spin-orbit
angle (i.e., parallel, polar, and anti-parallel orbits) for a while, but the
latter two states eventually approach the parallel spin-orbit configuration.
The intermediate spin-orbit angles as measured in recent observations are
difficult to be achieved. Therefore the current model cannot reproduce the
observed broad distribution of the spin-orbit angles, at least in its simple
form. This indicates that the observed diversity of the spin-orbit angles may
emerge from more complicated interactions with outer planets and/or may be the
consequence of the primordial misalignment between the proto-planetary disk and
the stellar spin, which requires future detailed studies.
