  We consider heavy particles immersed in a Fermi sea of light fermions, and
study the interaction between the heavy particles induced by the surrounding
light fermions. With the Born-Oppenheimer method, we analytically show that the
induced interaction between N heavy particles vanishes for any N in the limit
of high light-fermion density. The induced interaction vanishes even in the
unitarity regime. This suggests that the formation of N-body bound states
associated with the Efimov effect is suppressed in the presence of the dense
Fermi sea. We ascribe the vanishing induced interaction to the screening effect
in the neutral Fermi system.
