  Our recent N-body simulations of planetary system formation, incorporating
models for the main physical processes thought to be important during the
building of planets (i.e. gas disc evolution, migration, planetesimal/boulder
accretion, gas accretion onto cores, etc.), have been successful in reproducing
some of the broad features of the observed exoplanet population (e.g. compact
systems of low mass planets, hot Jupiters), but fail completely to form any
surviving cold Jupiters. The primary reason for this failure is rapid inward
migration of growing protoplanets during the gas accretion phase, resulting in
the delivery of these bodies onto orbits close to the star. Here, we present
the results of simulations that examine the formation of gas giant planets in
protoplanetary discs that are radially structured due to spatial and temporal
variations in the effective viscous stresses, and show that such a model
results in the formation of a population of cold gas giants. Furthermore, when
combined with models for disc photoevaporation and a central magnetospheric
cavity, the simulations reproduce the well-known hot-Jupiter/cold-Jupiter
dichotomy in the observed period distribution of giant exoplanets, with a
period valley between 10-100 days.
