ADDING LONG-WAVELENGTH MODES TO AN N-BODY SIMULATION

We present a new method to add long-wavelength power to an evolved N-b ody simulation, making use of the Zeldovich approximation to change po sitions and velocities of particles. We describe the theoretical frame work of our technique and apply it to a P(3)M cosmological simulation performed on a cube of 100 Mpc on a side, obtaining a new ''simulation '' of 800 Mpc on a side. We study the effect of the power added by lon g waves by means of several statistics of the density and velocity fie ld, and we suggest possible applications of our method to the study of the large-scale structure of the universe.