Minimum Scaling Model and Exact Exponents for the Nambu-Goldstone Modes in the Vicsek Model

We investigate the scaling behavior of Nambu-Goldstone modes in the ordered phase of the Vicsek model, introducing a phenomenological equation of motion incorporating a previously overlooked nonlinear term. This term arises from the interaction between velocity fields and density fluctuations, leading to new scaling behaviors. We derive exact scaling exponents in two dimensions, which reproduce the isotropic scaling behavior reported in a prior numerical simulation.