Smooth Structures on $M\times {\mathbb{S}}^k$

This paper explores various differentiable structures on the product manifold $M\times {\mathbb{S}}^k$, where $M$ is either a 4-dimensional closed, oriented, smooth manifold or a simply connected 5-dimensional closed, smooth manifold. We identify the possible stable homotopy types of $M$ and use it to calculate the concordance inertia group and the concordance structure set of $M\times {\mathbb{S}}^k$ for $1\le k\le 10$. These calculations enable us to further classify all manifolds that are homeomorphic to $\mathbb{C}{P}^2\times {\mathbb{S}}^k$, up to diffeomorphism, for each $4\le k\le 6$.