Smooth moduli spaces of associative submanifolds

Let $M^7$ be a smooth manifold equipped with a $G_2$-structure $\phi$, and $Y^3$ be an closed compact $\phi$-associative submanifold. In \cite{McL}, R. McLean proved that the moduli space \bm_{Y,\phi} of the $\phi$-associative deformations of $Y$ has vanishing virtual dimension. In this paper, we perturb $\phi$ into a $G_2$-structure $\psi$ in order to ensure the smoothness of \bm_{Y,\psi} near $Y$. If $Y$ is allowed to have a boundary moving in a fixed coassociative submanifold $X$, it was proved in \cite{GaWi} that the moduli space \bm_{Y,X} of the associative deformations of $Y$ with boundary in $X$ has finite virtual dimension. We show here that a generic perturbation of the boundary condition $X$ into $X'$ gives the smoothness of \bm_{Y,X'}. In another direction, we use the Bochner technique to prove a vanishing theorem that forces \bm_Y or \bm_{Y,X} to be smooth near $Y$. For every case, some explicit families of examples will be given.