  In this paper the collision of two cosmic string loops is studied. After
collision junctions are formed and the loops are entangled. We show that after
their formation the junctions start to unzip and the loops disentangle. This
analysis provides a theoretical understanding of the unzipping effect observed
in numerical simulations of a network of cosmic strings with more than one type
of cosmic strings. The unzipping phenomena have important effects in the
evolution of cosmic string networks when junctions are formed upon collision,
such as in a network of cosmic superstrings.
