Search for Majoron-emitting modes of double-beta decay of ^(136)Xe with EXO-200

EXO-200 is a single phase liquid xenon detector designed to search for neutrinoless double-beta decay of ^(136)Xe. Here, we report on a search for various Majoron-emitting modes based on 100 kg yr exposure of ^(136)Xe. A lower limit of T^(136)Xe_(1/2) > 1.2 × 10^(24)  yr at 90% C.L. on the half-life of the spectral index=1 Majoron decay was obtained, corresponding to a constraint on the Majoron-neutrino coupling constant of |⟨g^(M)_(ee)⟩| < (0.8–1.7) × 10^(−5).