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Roberto Mossa

Publications and source records attributed to Roberto Mossa.

At least 19 recordsLinked to original sources
arXiv2026

Bergman--Einstein Rigidity for Hartogs Domains over Bounded Homogeneous Domains

We prove a rigidity theorem for the Bergman metric on Hartogs domains over bounded homogeneous domains. Let $Ω\subset \mathbb C^n$ be a bounded homogeneous domain, let $K_Ω$ denote its Bergman kernel, and consider $$ Ω_{m,s}:=\{(z,ζ)\in Ω\times \mathbb C^m:\ \|ζ\|^2 -C_Ω. $$ For $s\neq 0$, we prove that the following conditions are equivalent: the Bergman metric of $Ω_{m,s}$ is Kähler--Einstein; $Ω_{m,s}$ is homogeneous; $Ω_{m,s}$ is biholomorphic to $\mathbb B^{n+m}$; and $Ω\cong\mathbb B^n$ with $s=\frac1{n+1}$. This gives a positive answer to Yau's question within this class and may be viewed as a Cheng-type rigidity phenomenon beyond the smoothly bounded strictly pseudoconvex setting. The proof combines the explicit formula for the Bergman kernel of $Ω_{m,s}$ with the structural invariants of the bounded homogeneous base.

math.DG↗
arXiv2025

The polydisk theorem for Hartogs domains over symmetric domains

We extend the polydisk theorem of [21], originally established for classical Cartan-Hartogs domains, to Hartogs domains over arbitrary (possibly reducible and exceptional) bounded symmetric domains. We further establish a dual counterpart of this result. As an application, we show that the dual of a Hartogs domain over a bounded symmetric domain admits no totally geodesic immersion into any compact Riemannian manifold, thereby broadening the rigidity phenomena obtained in [13].

math.DG↗
arXiv2025

On the Bergman metric of Cartan-Hartogs domains

We study the Bergman metric and introduce the Bergman dual on Cartan-Hartogs (CH) domains. For a bounded domain D in C^n with Bergman kernel K_D, we define the Bergman dual of (D, g_D) as (D*, g_D*), where D* is the maximal domain on which the modified kernel K_D*(z, zbar) = K_D(z, -zbar) is positive, and g_D* is the Kahler metric obtained from K_D*. For a Cartan-Hartogs domain M_{Omega, mu} we prove the equivalence of: (i) M_{Omega, mu} is biholomorphic to the unit ball; (ii) its Bergman metric is a Kahler-Ricci soliton; (iii) after rescaling by a constant factor, the Bergman dual is finitely projectively induced. Conditions (i) and (ii) are Bergman-metric analogues of classical rigidity for Kahler-Einstein metrics (related to Yau's problem and Cheng's conjecture) and to recent rigidity for Kahler-Ricci solitons. Condition (iii) emphasizes the duality viewpoint, inspired by bounded symmetric domains and their compact duals. We also compare our results with other canonical metrics on CH domains, namely g_{Omega, mu} and hat g_{Omega, mu}, and discuss open problems about the maximal domain on which the Bergman dual is defined.

math.CV↗
arXiv2025

Universal embeddings of flag manifolds and rigidity phenomena

We prove a universal embedding theorem for flag manifolds: every flag manifold admits a holomorphic isometric embedding into an irreducible classical flag manifold. This result generalizes the classical celebrated embedding theorems of Takeuchi [30] and Nakagawa-Takagi [27]. Using this embedding, we establish new rigidity phenomena for holomorphic isometries between homogeneous Kähler manifolds. As a first immediate consequence we show the triviality of a Kähler-Ricci soliton submanifod of $C \times Ω$, where $C$ is a flag manifold and $Ω$ is a homogeneous bounded domain. Secondly, we show that no \emph{weak-relative} relationship can occur among the fundamental classes of homogeneous Kähler manifolds: flat spaces, flag manifolds, and homogeneous bounded domains. Two Kähler manifolds are said to be \emph{weak relatives} if they share, up to local isometry, a common Kähler submanifold of complex dimension at least two. Our main result precisely shows that if $E$ is (possibly indefinite) flat, $C$ is a flag manifold, and $Ω$ is a homogeneous bounded domain, then: $E$ is not weak relative to $C\timesΩ$; $C$ is not weak relative to $E\timesΩ$; $Ω$ is not weak relative to $E\times C$. This extends, in two independent directions, the rigidity theorem of Loi-Mossa [22]: we pass from \emph{relatives} to the more flexible notion of \emph{weak relatives} and dispense with the earlier ''special'' restriction on the flag-manifold factor. This result also unifies previous rigidity results from the literature, e.g., [5, 6, 7, 9, 12, 13, 32].

math.DG↗
arXiv2024

Kähler duality and projective embeddings

Motivated by the duality theory between Hermitian symmetric spaces of noncompact and compact types, we introduce and examine the concept of Kähler duality between domains of $\mathbb C^n$.

math.DG↗
arXiv2023

Immersions of Sasaki-Ricci solitons into homogeneous Sasakian manifolds

We discuss local Sasakian immersion of Sasaki-Ricci solitons (SRS) into fiber products of homogeneous Sasakian manifolds. In particular, we prove that SRS locally induced by a large class of fiber products of homogeneous Sasakian manifolds are, in fact, $η$-Einstein. The results are stronger for immersions into Sasakian space forms. Moreover, we show an example of a Kähler-Ricci soliton on $\mathbb C^n$ which admits no local holomorphic isometry into products of homogeneous bounded domains with flat Kähler manifolds and generalized flag manifolds.

math.DG↗
arXiv2022

On holomorphic isometries into blow-ups of $\mathbb C^n$

We study the Kähler-Einstein manifolds which admits a holomorphic isometry into either the generalized Burns-Simanca manifold $(\tilde {\mathbb C}^n, g_S)$ or the Eguchi-Hanson manifold $(\tilde {\mathbb C}^2, g_{EH})$. Moreover, we prove that $(\tilde {\mathbb C}^n, g_S)$ and $(\tilde {\mathbb C}^2, g_{EH})$ are not relatives to any homogeneous bounded domain.

math.DG↗
arXiv2022

Holomorphic isometries into homogeneous bounded domains

We prove two rigidity theorems on holomorphic isometries into homogeneous bounded domains. The first shows that a Kähler-Ricci soliton induced by the homogeneous metric of a homogeneous bounded domain is trivial, i.e. Kähler-Einstein. In the second one we prove that a homogeneous bounded domain and the flat (definite or indefinite) complex Euclidean space are not relatives, i.e. they do not share a common Kähler submanifold (of positive dimension). Our theorems extend the results proved in [A. Loi, R. Mossa, Proc. Amer. Math. Soc. 149 (2021), no. 11, 4931-4941] and [X. Cheng, Y. Hao, Ann. Global Anal. Geom. 60 (2021), no. 1, 167-180] respectively.

math.DG↗
arXiv2021

A Cartan-Hartogs version of the Polydisk Theorem

We extend the Polydisk Theorem for symmetric bounded domains to Cartan-Hartogs domains, and apply it to prove that a Cartan-Hartogs domain inherits totally geodesic submanifolds from the bounded symmetric domain which is based on, and to give a characterization of Cartan-Hartogs's geodesics with linear support.

math.DG↗
arXiv2021

Subspace foliations and collapse of closed flat manifolds

We study relations between certain totally geodesic foliations of a closed flat manifold and its collapsed Gromov-Hausdorff limits. Our main results explicitly identify such collapsed limits as flat orbifolds, and provide algebraic and geometric criteria to determine whether they are singular.

math.DG↗
arXiv2020

On the $Δ$-property for complex space forms

Inspired by the work of Z. Lu and G. Tian [8], A. Loi, F. Salis and F. Zuddas address in [5] the problem of studying those Kähler manifolds satisfying the $Δ$-property, i.e. such that on a neighborhood of each of its points the $k$-th power of the Kähler Laplacian is a polynomial function of the complex Euclidean Laplacian, for all positive integer $k$. In particular, they conjectured that if a Kähler manifold satisfies the $Δ$-property then it is a complex space form. This paper is dedicated to the proof of the validity of this conjecture.

math.DG↗
arXiv2020

Symplectic geometry of Cartan-Hartogs domains

This paper studies the geometry of Cartan-Hartogs domains from the symplectic point of view. Inspired by duality between compact and noncompact Hermitian symmetric spaces, we construct a dual counterpart of Cartan-Hartogs domains and give explicit expression of global Darboux coordinates for both Cartan-Hartogs and their dual. Further, we compute their symplectic capacity and show that a Cartan-Hartogs admits a symplectic duality if and only if it reduces to be a complex hyperbolic space.

math.DG↗
arXiv2019

On the diastatic entropy and C^1-rigidity of complex hyperbolic manifolds

Let f:(Y,g)->(X,g_0) be a non zero degree continuous map between compact Kähler manifolds of dimension greater or equal to 2, where g_0 has constant negative holomorphic sectional curvature. Adapting the Besson-Courtois-Gallot barycentre map techniques to the Kähler setting, we prove a gap theorem in terms of the degree of f and the diastatic entropies of (Y, g) and (X,g_0), which extends the rigidity result proved by the author in [13].

math.DG↗
arXiv2017

Bochner coordinates on flag manifolds

We find necessary and sufficient conditions under which the complex coordinates on a flag manifold of a classical group described in [2] are Bochner coordinates.

math.DG↗
arXiv2015

Diastatic entropy and rigidity of hyperbolic manifolds

Let $f: Y \rightarrow X$ be a continuous map between a compact real analytic Kähler manifold $(Y,g)$ and a compact complex {hyperbolic manifold} $(X,g_0)$. In this paper we give a lower bound of the diastatic entropy of $(Y,g)$ in terms of the diastatic entropy of $(X,g_0)$ and the degree of $f$. When the lower bound is attained we get geometric rigidity theorems for the diastatic entropy analogous to the ones obtained by G. Besson, G. Courtois and S. Gallot [2] for the volume entropy. As a corollary, when $X=Y$, we show that the minimal diastatic entropy is achieved if and only if $g$ is holomorphically or anti-holomorphically isometric to the hyperbolic metric $g_0$.

math.DG↗
arXiv2015

Minimal symplectic atlases of Hermitian symmetric spaces

In this paper we compute the minimal number of Darboux chart needed to cover a Hermitian symmetric space of compact type in terms of the degree of their embeddings in $\mathbb{C} P^N$. The proof is based on the recent work of Y. B. Rudyak and F. Schlenk [18] and on the symplectic geometry tool developed by the first author in collaboration with A. Loi and F. Zuddas [12]. As application we compute this number for a large class of Hermitian symmetric spaces of compact type.

math.SG↗
arXiv2015

Upper and lower bounds for the first eigenvalue and the volume entropy of noncompact Kähler manifolds

We find upper and lower bounds for the first eigenvalue and the volume entropy of a noncompact real analytic Kähler manifold, in terms of Calabi's diastasis function and diastatic entropy, which are sharp in the case of the complex hyperbolic space. As a corollary we obtain explicit lower bounds for the first eigenvalue of the geodesic balls of an Hermitian symmetric space of noncompact type.

math.DG↗