Cohomology of the diffeomorphism group of the connected sum of two generic lens spaces

We consider the connected sum of two three-dimensional lens spaces $L_1\mathrm{\#}{L}_2$, where $L_1$ and $L_2$ are non-diffeomorphic and are of a certain “generic” type. Our main result is the calculation of the cohomology ring $H^{\ast }(B\text{Diff}(L_1\mathrm{\#}{L}_2);\mathbb{Q})$, where $\text{Diff}(L_1\mathrm{\#}{L}_2)$ is the diffeomorphism group of $M$ equipped with the $C^{\mathrm{\infty }}$-topology. We know the homotopy type of the diffeomorphism groups of generic lens spaces this, combined with a theorem of Hatcher forms the basis of our argument.