Abstract

We discuss the contribution of axion-like excitations (ALE) to the vacuum birefringence in the limit mA ??, where mA is the mass of the excitation and ? the energy of test photons interacting with an external (intense) magnetic field. The relevance of this term with respect to the QED contribution depends on the ratio gA/mA and, from present bounds on the mass and the coupling constant gA, we find that in the present low energy regime, it ranges from 10-14 to 102 suggesting an interesting alternative to explore. © 2009 World Scientific Publishing Company.