  The existence of a scaling evolution for cosmic string loops in an expanding
universe is demonstrated for the first time by means of numerical simulations.
In contrast with what is usually assumed, this result does not rely on any
gravitational back reaction effect and has been observed for loops as small as
a few thousandths the size of the horizon. We give the energy and number
densities of expected cosmic string loops in both the radiation and matter
eras. Moreover, we quantify previous claims on the influence of the network
initial conditions and the formation of numerically unresolved loops by showing
that they only concern a transient relaxation regime. Some cosmological
consequences are discussed.
