  Exoplanets show a pile-up of Jupiter-size planets in orbits with a 3-day
period. A fraction of these hot Jupiters have retrograde orbits with respect to
the parent star's rotation. To explain these observations we performed a series
of numerical integrations of planet scattering followed by the tidal
circularization. We considered planetary systems having 3 and 4 planets
initially. We found that the standard Kozai migration is an inefficient
mechanism for the formation of hot Jupiters.
  Our results show the formation of two distinct populations of hot Jupiters.
The inner population of hot Jupiters with semimajor axis a < 0.03 AU formed in
the systems where no planetary ejections occurred. This group contained a
significant fraction of highly inclined and retrograde orbits, with
distributions largely independent of the initial setup. However, our follow-up
integrations showed that this populations was transient with most planets
falling inside the Roche radius of the star in <1 Gyr. The outer population of
hot Jupiters formed in systems where at least one planet was ejected. This
population survived the effects of tides over >1 Gyr. The semimajor axis
distribution of Population II fits nicely the observed 3-day pile-up.
  The inclination distribution of the outer hot planets depends on the number
of planets in the initial systems and the 4-planet case showed a larger
proportion (up to 10%), and a wider spread in inclination values. As the later
results roughly agrees with observations, this may suggest that the planetary
systems with observed hot Jupiters were originally rich in the number of
planets, some of which were ejected. In a broad perspective, our work therefore
hints on an unexpected link between the hot Jupiters and recently discovered
free floating planets.
