  This article investigates several properties related to densities of
solutions X to differential equations driven by a fractional Brownian motion
with Hurst parameter H>1/4. We first determine conditions for strict positivity
of the density of X_t. Then we obtain some exponential bounds for this density
when the diffusion coefficient satisfies an elliptic type condition. Finally,
still in the elliptic case, we derive some bounds on the hitting probabilities
of sets by fractional differential systems in terms of Newtonian capacities.
