  Recent experiments performed on weakly pinched quantum point contacts, have
shown a resistance that tend to decrease at low source drain voltage. We show
that enhanced Coulomb interactions, prompt by the presence of the point
contact, may lead to anomalously large multiple-particle scattering at finite
bias voltage. These processes tend to decrease at low voltage, and thus may
account for the observed reduction of the resistance. We concentrate on the
case of a normal point contact, and model it by a spinfull interacting
Tomonaga-Luttinger liquid, with a single impurity, connected to non interacting
leads. We find that sufficiently strong Coulomb interactions enhance
two-electron scattering, so as these dominate the conductance. Our calculation
shows that the effective charge, probed by the shot noise of such a system,
approaches a value proportional to e* = 2e at sufficiently large backscattering
current. This distinctive hallmark may be tested experimentally. We discuss
possible applications of this model to experiments conducted on Hall bars.
