Universal properties of three-dimensional magnetohydrodynamic turbulence: do Alfven waves matter?

We analyse the effects of the propagating Alfven waves, arising due to non-zero mean magnetic fields, on the nonequilibrium steady states of three-dimensional (3D) homogeneous magnetohydrodynamic (MHD) turbulence. In particular, the effects of Alfven waves on the universal properties of 3DMHD turbulence are studied in a one-loop self-consistent mode-coupling approach. We calculate the kinetic- and magnetic-energy spectra. We find that even in the presence of a mean magnetic field the energy spectra are Kolmogorov-like, i.e., scale as k(-5/3) in the inertial range where k is a Fourier wavevector belonging to the inertial range. We also elucidate the multiscaling of the structure functions in a log-normal model by evaluating the relevant intermittency exponents, and our results suggest that the multiscaling deviations from the simple Kolmogorov scaling of the structure functions decrease with increasing strength of the mean magnetic field. Our results compare favourably with many existing numerical and observational results.