
Let \(G\) be a semisimple (connected) complex algebraic group with Lie algebra \(\mathfrak{g}\), on which \(G\) acts by the adjoint action, and let \(P\) be a standard parabolic subgroup of \(G\) with Lie algebra \(\mathfrak{p}\). There is a unique nilpotent \(G\)-orbit \(\mathcal{O}_{\mathfrak{p}}\) such that the set \(\mathcal{O}_{\mathfrak{p}} \cap \mathfrak{n}_{\mathfrak{p}}\) is open and dense in \(\mathfrak{n}_{\mathfrak{p}}\), the nilradical of \(\mathfrak{p}\), and is called the Richardson orbit associated with \(\mathfrak{p}\). Let \(G \times ^P\mathfrak{n}_{\mathfrak{p}}\) be the quotient space of \(G \times \mathfrak{n}_{\mathfrak{p}}\) by the right action of \(P\) given by \((g,x).p = (gp, p^{-1}.x)\), where \(g \in G\), \(x \in \mathfrak{n}_{\mathfrak{p}}\), and \(p \in P\). The mapping \(f_{\mathfrak{p}}: G \times ^P\mathfrak{n}_{\mathfrak{p}} \rightarrow \mathfrak{g}\) defined by \(g \ast x \mapsto g.x\), where \(g \ast x \in G \times ^P\mathfrak{n}_{\mathfrak{p}}\) is the equivalence class of \((g,x)\), is called the generalized Springer resolution. After the proof of a general result on some irreducible components of the fibers of \(f_{\mathfrak{p}}\), the author investigates the generalized Springer resolution when \(G = \mathbf{SL}(n,\mathbb{C})\). He shows that, in this case, the generalized Springer fiber \(f_{\mathfrak{p}}^{-1}(x)\) is isomorphic either to a Dynkin curve or to a projective space for all \(x \in \mathcal{O} \cap \mathfrak{n}_{\mathfrak{p}}\), where \(\mathcal{O}\) is any nilpotent \(G\)-orbit included in the closure of \(\mathcal{O}_{\mathfrak{p}}\). Then, he applies results of [\textit{H. Esnault}, Singularités rationelles et groupes algébriques, Thèse de 3ème cycle, Paris VII (1976)] to prove that, in some cases, the generalized Springer resolution restricts to the minimal resolution of a normal surface with a rational double point of type \(A_r\), for a well-defined \(r\).
Mathematics(all), rational double point, Simple singularity, Springer fibers, special linear group, Semisimple Lie groups and their representations, Richardson orbit, Linear algebraic groups over the reals, the complexes, the quaternions, minimal resolution, Springer resolution, Special linear group, Noncompact Lie groups of transformations, Dynkin curve
Mathematics(all), rational double point, Simple singularity, Springer fibers, special linear group, Semisimple Lie groups and their representations, Richardson orbit, Linear algebraic groups over the reals, the complexes, the quaternions, minimal resolution, Springer resolution, Special linear group, Noncompact Lie groups of transformations, Dynkin curve
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