Except graviton, the only theory-motivated particle coupling to curvature square is the model-independent (MI) axion arising from string compactification. The recent LIGO observations of gravity waves from mergers of two black holes constrain the mass of graviton < 10^-22 eV, which arises from merging black hole masses of O(tens of Solar mass). A similar study was done for the MI axion. Since the MI axion decay constant is about 10¹⁶ GeV, we derived the black hole mass limit of two merging black holes, < 2 x 10¹⁴ kg, for the effect to be significant.

Keywords: Model-independent axion, Gravity wave, Graviton mass