  The formation of gas-giant planets within the lifetime of a protoplanetary
disk is challenging especially far from a star. A promising model for the rapid
formation of giant-planet cores is pebble accretion in which gas drag during
encounters leads to high accretion rates. Most models of pebble accretion
consider disks with a monotonic, radial pressure profile. This causes a
continuous inward flux of pebbles and inefficient growth. Here we examine
planet formation in a disk with multiple, intrinsic pressure bumps. In the
outer disk, pebbles become trapped near these bumps allowing rapid growth under
suitable conditions. In the inner disk, pebble traps may not exist because the
inward gas advection velocity is too high. Pebbles here are rapidly removed. In
the outer disk, growth is very sensitive to the initial planet mass and the
strength of turbulence. This is because turbulent density fluctuations raise
planetary eccentricities, increasing the planet-pebble relative velocity.
Planetary seeds above a distance-dependent critical mass grow to a Jupiter mass
in 0.5--3 million years out to at least 60 AU in a 0.03 solar-mass disk.
Smaller bodies remain near their initial mass, leading to a sharp dichotomy in
growth outcomes. For turbulent alpha = 1e-4, the critical masses are 1e-4 and
1e-3 Earth masses at 9 and 75 AU, respectively. Pressure bumps in disks may
explain the large mass difference between the giant planets and Kuiper belt
objects, and also the existence of wide-orbit planets in some systems.
