(2+1)-dimensional chern-simons bi-gravity with ads lie bialgebra as an interacting theory of two massless spin-2 fields

We introduce a new lie bialgebra structure for the anti de sitter (ads) lie algebra in (2+1)-dimensional spacetime. by gauging the resulting textit{ads lie bialgebra}, we write a chern-simons gauge theory of bi-gravity involving two dreibeins rather than two metrics, which describes two interacting massless spin-2 fields. our ghost-free bi-gravity model which has no any local degrees of freedom, has also a suitable free field limit. by solving its equations of motion, we obtain a textit{new black hole} solution which has two curvature singularities and two horizons. we also study cosmological implications of this massless bi-gravity model.