The article considers implications of tilt symmetry (symmetry with respect to
tilting of the coordinate axis with respect to which vortex motion is studied)
in the non-linear dynamics of Kelvin waves. The conclusion is that although the
spectrum of Kelvin wave is not tilt-invariant, this does not compromise tilt
invariance of the Kelvin-wave cascade vividly argued now in the theory of
superfluid turbulence. The article investigates the effect of strong kelvon
interaction on the power-law exponent for the Kelvin-wave cascade and suggests
a simple picture of the crossover from the classical Kolmogorov cascade to the
quantum Kelvin-wave cascade, which does not encounter with mismatch of the
energy distributions at the crossover and does not require a broad intermediate
interval for realization of the crossover.Comment: 7 pages, 1 figur