arXiv subjects
Publications and source records attributed to Andrea F. Spiro.
We classify all compact simply connected homogeneous CR manifolds $M$ of codimension one and with non-degenerate Levi form up to CR equivalence. The classification is based on our previous results and on a description of the maximal connected compact group $G(M)$ of automorphisms of $M$. We characterize also the standard homogeneous CR manifolds as the homogeneous CR manifolds whose group $G(M)$ in not semisimple.
An explicit classification of simply connected compact homogeneous CR manifolds G/L of codimension one, with non-degenerate Levi form, is given. There are three classes of such manifolds: a) the standard CR homogeneous manifolds which are homogeneous S^1-bundles over a flag manifold F, with CR structure induced by an invariant complex structure on F; b) the Morimoto-Nagano spaces, i.e. sphere bundles $S(N)\subset TN$ of a compact rank one symmetric space N = G/H, with the CR structure induced by the natural complex structure of $TN = G^\C/H^\C$; c) the following manifolds: $SU_n/T^1\cdot SU_{n-2}$, $SU_p\times SU_q/T^1 \cdot U_{p-2}\cdot U_{q-2}$, $SU_n/T^1\cdot SU_2\cdot SU_2\cdot SU_{n-4}$, $SO_{10}/T^1\cdot SO_6$, $E_6/T^1\cdot SO_8$; these manifolds admit canonical holomorphic fibrations over a flag manifold (F,J_F) with typical fiber S(S^k), where k = 2, 3, 5, 7 or 9, respectively; the CR structure is determined by the invariant complex structure J_F on F and by an invariant CR structure on the typical fiber, depending on one complex parameter.
In this article, we consider a bounded pseudoconvex domain in ${\bf C}^2$ satifying: (a) it admits a proper holomorphic mapping $f$ onto the unit ball $B^2$, and (b) it is simply connected and has a real analytic boundary. According to [Barletta-Bedford, Indiana U. Math. J, 39(1985), 315-338], the strong pseudconvexity of $B^2$ alone yields that such a domain is "weakly spherical" at the boundary points that are at the same time a smooth point of the branch locus $Z_{df} = \{\det(J_{\bf C} f) = 0\}$. (Notice that [Diederich-Fornaess, Math. Ann., 282 (1988), 681-700] implies that $f$ as well as $Z_{df}$ extends holomorphically across the boundaries.) Our main contribution in this paper is that we have discovered a stronger rigidity (both local and global) in case the target domain is the unit ball. The main results are: THEOREM ("Local Rigidity"): Let $(M,o)$ be a real analytic normalized weakly spherical pointed CR hypersurface in ${\bf C}^2$ of order $k_0 > 1$. Let $(Σ, o)$ be the pointed Siegel hypersurface given by the defining equation $Re w - |z|^2 = 0$. If there is a holomorphic mapping $F:(M,o) \to (Σ,o)$ for which $o$ is a regular branch point, then (1) $(M,o)$ is defined by the equation $Re w - |z|^{2k_0} = 0$, and (2) $F(z,w)$ is equivalent to $(z,w) \mapsto (z^{k_0},w)$ up to a composition with elements in $Aut (M,o)$ and $Aut (Σ,o)$. THEOREM ("Global Rigidity"): Let $D$ and $f:D \to B^2$ be as above, and let $f$ be generically $m$-to-1. Assume that its branch locus $Z_{df}$ admits an analytic component $V$ with the following properties: (1) $f$ is locally a $m$-to-1 branched covering with branch locus $V$ at every point of $V \cap \partial D$; (2) $V \cap \partial D$ is connected and contains no singular point of the variety $Z_{df}$. Then $D$ is biholomorphic to $E_m = \{|z|^{2m} + |w|^2 < 1\}$.