  When considering the migration of Jupiter and Saturn, a classical result is
to find the planets migrating outwards and locked in the 3:2 mean motion
resonance (MMR). These results were obtained in the framework of viscously
accreting discs, in which the observed stellar accretion rates constrained the
viscosity values. However, it has recently been shown observationally and
theoretically that discs are probably less viscous than previously thought.
Therefore, in this paper, we explore the dynamics of pairs of giant planets in
low-viscosity discs. We performed two-dimensional hydrodynamical simulations
using the grid-based code FARGOCA. In contrast to classical viscous discs, we
find that the outer planet never crosses the 2:1 resonance and the pair does
not migrate outwards. After a wide parameter exploration, including the mass of
the outer planet, we find that the planets are primarily locked in the 2:1 MMR
and in some cases in the 5:2 MMR. We explain semi-analytically why it is not
possible for the outer planet to cross the 2:1 MMR in a low-viscosity disc. We
find that pairs of giant planets migrate inwards in low-viscosity discs.
Although, in some cases, having a pair of giant planets can slow down the
migration speed with respect to a single planet. Such pairs of slowly migrating
planets may be located, at the end of the disc phase, in the population of
exoplanets of 'warm Jupiters'. However, the planets never migrate outwards.
These results could have strong implications on the Solar System's formation
scenarios if the Sun's protoplanetary disc had a low viscosity.
