  We investigate by Monte Carlo simulations the zipping and unzipping dynamics
of two polymers connected by one end and subject to an attractive interaction
between complementary monomers. In zipping, the polymers are quenched from a
high temperature equilibrium configuration to a low temperature state, so that
the two strands zip up by closing up a "Y"-fork. In unzipping, the polymers are
brought from a low temperature double stranded configuration to high
temperatures, so that the two strands separate. Simulations show that the
unzipping time, $\tau_u$, scales as a function of the polymer length as $\tau_u
\sim L$, while the zipping is characterized by anomalous dynamics $\tau_z \sim
L^\alpha$ with $\alpha = 1.37(2)$. This exponent is in good agreement with
simulation results and theoretical predictions for the scaling of the
translocation time of a forced polymer passing through a narrow pore. We find
that the exponent $\alpha$ is robust against variations of parameters and
temperature, whereas the scaling of $\tau_z$ as a function of the driving force
shows the existence of two different regimes: the weak forcing ($\tau_z \sim
1/F$) and strong forcing ($\tau_z$ independent of $F$) regimes. The crossover
region is possibly characterized by a non-trivial scaling in $F$, matching the
prediction of recent theories of polymer translocation. Although the
geometrical setup is different, zipping and translocation share thus the same
type of anomalous dynamics. Systems where this dynamics could be experimentally
investigated are DNA (or RNA) hairpins: our results imply an anomalous dynamics
for the hairpins closing times, but not for the opening times.
