Hilbert schemes of rational curves on Fano hypersurfaces

In this paper we try to further explore the linear model of the moduli of rational maps. Our attempt yields following results. Let $X\subset {\mathbf{P}}^n$ be a generic hypersurface of degree $h$. Let $R_d(X,h)$ denote the open set of the Hilbert scheme parameterizing irreducible rational curves of degree $d$ on $X$. We obtain that (1) If $4\le h\le n-1$, $R_d(X,h)$ is an integral, local complete intersection of dimension \begin{equation} (n+1-h)d+n-4. \end{equation} (2) If furthermore $(h^2-n)d+h\le 0$ and $h\ge 4$, in addition to part (1), $R_d(X,h)$ is also rationally connected.