Some rational homology computations for diffeomorphisms of odd-dimensional manifolds

We calculate the rational cohomology of the classifying space of the diffeomorphism group of the manifolds \(U_{g,1}^n:= \#^g(S^n \times S^{n+1})\setminus \mathrm{int}{D^{2n+1}}\), for large \(g\) and \(n\), up to approximately degree \(n\). The answer is that it is a free graded commutative algebra on an appropriate set of Miller--Morita--Mumford classes. Our proof goes through the classical three-step procedure: (a) compute the cohomology of the homotopy automorphisms, (b) use surgery to compare this to block diffeomorphisms, (c) use pseudoisotopy theory and algebraic \(K\)-theory to get at actual diffeomorphism groups.