Relaxing axions

A mechanism for lifting the cosmological upper bound on the axion decay constant, f(a), is proposed. It entails the near masslessness of the radial mode whose vacuum expectation value is f(a). Energy in the coherent oscillations of the axion field in the early universe gets fed into the motion of the radial mode, from which it is then redshifted away. It is found that the initial value of f(a) can be at scales between 2x10(14) GeV and 10(16) GeV. This evolves with time to values close to the Planck scale. It is suggested that the nearly massless radial mode might play the role of quintessence. (C) 1999 Published by Elsevier Science B.V. All rights reserved.