  We propose a mechanism by which dust rings in protoplanetary disks can form
and be long-lasting compared to gas rings. This involves the existence of a
pressure maximum which traps dust either in between two gap-opening planets or
at the outermost gap edge of a single or multiple planet system, combined with
the decoupling of large dust particles from the gas. We perform 2D gas
hydrodynamical simulations of disks with one and two giant planets which may
open deep or partial gaps. A gas ring forms in between two planets such that
the surface mass density is higher than on either side of it. This ring is a
region of pressure maximum where we expect large grains, which are marginally
coupled to the gas and would otherwise be subject to radial drift, to collect.
Such a pressure maximum also occurs at the outermost gap edge in a disk with
one or more planets. We infer the dust evolution in these regions as the gas
disk evolves, to understand the longer term behavior of the resulting dust
rings. Over time the gas surface density in the ring(s) decreases, which may
cause the larger trapped particles to decouple. Consequently, these particles
are expected to stay in ring structure(s) longer than the gas. For a Minimum
Mass Solar Nebula model, we expect that millimeter and centimeter-sized grains
in the outer O(10) au would most likely undergo this trapping and decoupling
process.
