Numerical analysis of formation and evolution of global strings in 2+1 dimensions

We simulate the formation and the evolution of global strings taking into account the expansion of the universe and the concomitant change of the effective potential, that is, the change from the restoration stage of the global {\it U}(1)-symmetry to the broken stage. Starting from the thermal equilibrium state, we run simulations for 100 sets of different initial conditions in 2+1 dimensions. As a result, we find deviation from scale invariance. This is because the energy loss mechanism is pair annihilation rather than intercommutation, so that a string and an anti-string attract each other under a logarithmic potential.