Quantization leading to a natural flattening of the axion potential

Starting from the general cosine form for the axion effective potential, we quantize the axion and show that the result is described by a naturally flat potential, if interactions with other particles are not considered. This feature therefore restores the would-be Goldstone-boson nature of the axion, and we calculate the corresponding vacuum energy density, which does not need to be too large by orders of magnitude compared to Dark Energy.