A modification of the relation between axion mass and the PQ constant per- mits a relaxation of the astrophysical constraints, considerably enlarging the allowed axion parameter space. We develop this idea in this paper, discussing a model for an ultramassive axion, which essentially represents a supersymmetric Weinberg-Wilczek axion of the mirror world. The experimental and astrophysical limits allow a PQ scale fa ā¼ 104 ā106 GeV and a mass ma ā¼ MeV, which can be accessible for future experiments.
On a phenomenological ground, such an ultramassive axion turns out to be quite inter- esting. It can be produced during the gravitational collapse or during the merging of two compact objects, and its subsequent decay into e+eā provides an efficient mechanism for the transfer of the gravitational energy of the collapsing system to the electron-positron plasma. This could resolve the energy budget problem in the Gamma Ray Bursts and also help in understanding the SN type-II explosion phenomena.
