I am trying to understand more about geometric interpretation of vertex algebras following "Vertex Algebras and Algebraic Curves" by Ben-Zvi and Frenkel, but I am in trouble with the following constrution:

Let $X$ be a smooth curve over a algebraically closed field $k$ of characteristic zero, $p \in X$ a $k-$point and $\hat{\mathcal{O}_p}$ be the completation of the local ring, then $\hat{\mathcal{O}_p} \simeq k[[z]]$. Let $G_0(R) = \{f \in \mathrm{Aut}(R[[z]])| f(z) \in z R[[z]] \}$ be de group-scheme of automorphims of the formal disc preserving the origin and $\mathrm{Coord}_p = \{\hat{\mathcal{O}_p} \to k[[z]] \,\,\,\text{isomorphism}\}$, $\mathrm{Coord}_p$ is a $G_0(k)-$right torsor. I would like to construct a $G_0-$principal bundle $\mathrm{Coord}_X$ over $X$ with fiber $\mathrm{Coord}_p$ at $p$. Frenkel and Ben-Zvi actually gives a functor of points $F(R) = \{f: R[[z]] \to X \,\, \text{with non-vanishing differential at}\,\, z=0\}$.

I am looking for references to:

- Principal bundles over schemes (with Zariski opens) and associated bundle;
- A construction of this $\mathrm{Coord}_X$ or anything similar to understand better what is going on.