Axions and the pulsation periods of variable white dwarfs revisited

Axionsare the natural consequence of the introduction of the Peccei-Quinn symmetry to solve the strong CP problem. All the efforts to detect such elusive particles have failed up to now. Nevertheless, it has been recently shown that the luminosity functionof white dwarfsis best fitted if axionswith a mass of a few meV are included in the evolutionary calculations. Our aim is to show that variable white dwarfscan provide additional and independent evidence about the existence of axions. The evolution of a white dwarfis a slow cooling process that translates into a secular increase of the pulsation periods of some variable white dwarfs, the so-called DAV and DBV types. Since axionscan freely escape from such stars, their existence would increase the cooling rate and, consequently, the rate of change of the periods as compared with the standard ones. The present values of the rate of change of the pulsation period of G117-B15A are compatible with the existence of axionswith the masses suggested by the luminosity functionof white dwarfs, in contrast with previous estimations. Furthermore, it is shown that if such axionsindeed exist, the drift of the periods of pulsation of DBV stars would be noticeably perturbed.