arXiv subjects

Sayani Bera

Publications and source records attributed to Sayani Bera.

14 recordsLinked to original sources

arXiv2026

Rigidity of the escaping set of polynomial automorphisms of $\mathbb{C}^2$

Let $H$ be a polynomial automorphism of $\mathbb{C}^2$ of positive entropy and degree $d \ge 2$. We prove that the escaping set $U^+$ (or equivalently, the non-escaping set $K^+$), of $H$ is rigid under the action of holomorphic automorphisms of $\mathbb{C}^2$. Specifically, every holomorphic automorphism of $\mathbb{C}^2$ that preserves $U^+$ essentially takes the form $L \circ H^s$ where $s \in \mathbb{Z}$ and $L$ belongs to a finite cyclic group of affine maps that preserve the escaping set. Second, note that the sub-level sets $\{G^+ < c\}$, $c > 0$, of the Greens function $G^+$ associated with the map $H$ are canonical examples of Short $\mathbb{C}^2$s. As a consequence of the above theorem, we show that the holomorphic automorphisms of these Short $\mathbb{C}^2$s are affine automorphisms of $\mathbb{C}^2$ preserving the escaping set $U^+$. Hence, the automorphism group of these Short $\mathbb{C}^2$s are the same for every $c>0$ and is a finite cyclic group.

math.CV↗

arXiv2025

Rigidity of the escaping set of certain H\'enon maps

Let $H$ be a H\'enon map of the form $H(x,y)=(y,p(y)-ax)$. We prove that the escaping set $U^+$ (or equivalently, the non-escaping set $K^+$), of $H$ is rigid under the actions of automorphisms of $\mathbb{C}^2$ if the degree of $H=d\le |a|$. Specifically, every automorphism of $\mathbb{C}^2$ that preserves $U^+$, essentially takes the form $C \circ H^s$ where $s \in \mathbb{Z}$, and $C(x,y)=(\eta x, \eta^d y)$ with $\eta$ some $(d^2-1)$-root of unity. Consequently, we show that the automorphisms of the short $\mathbb{C}^2$'s, obtained as the sub-level sets of the (positive) Green's function corresponding to the H\'enon map $H$ for strictly positive values, are essentially linear maps of $\mathbb{C}^2$ preserving the escaping set $U^+$. Hence, the automorphism groups of these short $\mathbb{C}^2$'s are the same, finite, and form a subgroup of $\mathbb{Z}_{d^2-1}$.

math.CV↗

arXiv2023

Dynamics of semigroups of Hénon maps

The goal of this article is two fold. Firstly, we explore the dynamics of a semigroup of polynomial automorphisms of $\mathbb{C}^2$, generated by a finite collection of Hénon maps. In particular, we construct the positive and negative dynamical Green's functions $G_{\mathscr{G}}^\pm$ and the corresponding dynamical Green's currents $μ_{\mathscr{G}}^\pm$ for a semigroup $\mathcal{S}$, generated by a collection ${\mathscr{G}}.$ Using them, we show that the positive (or negative) Julia set of the semigroup $\mathcal{S}$, i.e., $\mathcal{J}_{\mathcal{S}}^+$ (or $\mathcal{J}_{\mathcal{S}}^-$) is equal to the closure of the union of individual positive (or negative) Julia sets of the maps, in the semigroup $\mathcal{S}$. Furthermore, we prove that $μ_{\mathscr{G}}^+$ is supported on the whole of $\mathcal{J}_{\mathcal{S}}^+$ and is also the unique positive closed $(1,1)$-current supported on $\mathcal{J}_{\mathcal{S}}^+$, satisfying a semi-invariance relation that depends on the generating set ${\mathscr{G}}$. Secondly, we study the dynamics of a non-autonomous sequence of Hénon maps, say $\{h_k\}$, contained in the semigroup $\mathcal{S}$. Similarly, as above, here too, we construct the non-autonomous dynamical positive and negative Green's function and the corresponding dynamical Green's currents. Further, we use the properties of Green's function to conclude that the non-autonomous attracting basin of any such sequence $\{h_k\}$, sharing a common attracting fixed point, is biholomorphic to $\mathbb{C}^2.$

math.CV↗

arXiv2022

Uniform non-autonomous basins of attraction

It has been conjectured that every stable manifold arising from a holomorphic automorphism, that acts hyperbolically on a compact invariant set, is biholomorphic to complex Euclidean space. Such stable manifolds are known to be biholomorphic to the basin of a uniformly attracting family of holomorphic maps. It is shown that the basin of a uniformly attracting family of holomorphic maps is biholomorphic to complex Euclidean space and this resolves the conjecture on the biholomorphism type of such stable manifolds affirmatively.

math.CV↗

arXiv2022

On the automorphism group of certain Short $\mathbb C^2$'s

For a Hénon map of the form $H(x, y) = (y, p(y) - ax)$, where $p$ is a polynomial of degree at least two and $a \not= 0$, it is known that the sub-level sets of the Green's function $G^+_H$ associated with $H$ are Short $\mathbb C^2$'s. For a given $c > 0$, we study the holomorphic automorphism group of such a Short $\mathbb C^2$, namely $Ω_c = \{ G^+_H < c \}$. The unbounded domain $Ω_c \subset \mathbb C^2$ is known to have smooth real analytic Levi-flat boundary. Despite the fact that $Ω_c$ admits an exhaustion by biholomorphic images of the unit ball, it turns out that its automorphism group, Aut$(Ω_c)$ cannot be too large. On the other hand, examples are provided to show that these automorphism groups are non-trivial in general. We also obtain necessary and sufficient conditions for such a pair of Short $\mathbb C^2$'s to be biholomorphic.

math.CV↗

arXiv2021

On a spectral version of Cartan's theorem

For a domain $Ω$ in the complex plane, we consider the domain $S_n(Ω)$ consisting of those $n\times n$ complex matrices whose spectrum is contained in $Ω$. Given a holomorphic self-map $Ψ$ of $S_n(Ω)$ such that $Ψ(A)=A$ and the derivative of $Ψ$ at $A$ is identity for some $A\in S_n(Ω)$, we investigate when the map $Ψ$ would be spectrum-preserving. We prove that if the matrix $A$ is either diagonalizable or non-derogatory then for most domains $Ω$, $Ψ$ is spectrum-preserving on $S_n(Ω)$. Further, when $A$ is arbitrary, we prove that $Ψ$ is spectrum-preserving on a certain analytic subset of $S_n(Ω)$.

math.CV↗

arXiv2019

Rigidity of Julia sets of families of biholomorphic mappings in higher dimension

The goal of this article is to study a rigidity property of Julia sets of certain classes of automorphisms in $\mathbb{C}^k$, $k \ge 3.$ First, we study the relation between two polynomial shift-like maps in $\mathbb{C}^k$, $k \ge 3$, that share the same backward and forward Julia sets (or non-escaping sets). Secondly, we study the relationship between any pair of skew products of Hénon maps in $\mathbb{C}^3$ having the same forward and backward Julia sets.

math.CV↗

arXiv2019

Rigidity Theorems for Hénon maps-II

The purpose of this note is to explore further the rigidity properties of Hénon maps from arXiv:1806.08189. For instance, we show that if $H$ and $F$ are Hénon maps with the same Green measure ($μ_H=μ_F$), or the same filled Julia set ($K_H=K_F$), or the same Green function ($G_H=G_F$), then $H^2$ and $F^2$ have to commute. This, in turn, gives that $H$ and $F$ have the same non-escaping sets. Further we prove that, either of the association of a Hénon map $H$ to its Green measure $μ_H$ or to its filled Julia set $K_H$ or to its Green function $G_H$ is locally injective.

math.CV↗

arXiv2018

Polynomial shift--like maps in $\mathbb{C}^k$

The purpose of this article is to explore a few properties of polynomial shift-like automorphisms of $\mathbb{C}^k.$ We first prove that a $ν-$shift-like polynomial map (say $S_a$) degenerates essentially to a polynomial map in $ν-$dimensions as $a \to 0.$ Secondly, we show that a shift-like map obtained by perturbing a hyperbolic polynomial (i.e., $S_a$, where $|a|$ is sufficiently small) has finitely many Fatou components, consisting of basins of attraction of periodic points and the component at infinity.

math.CV↗

arXiv2018

A rigidity theorem for Hénon maps

The purpose of this note is two fold. First, we study the relation between a pair of Hénon maps that share the same forward and backward non-escaping sets. Second, it is shown that there exists a continuum of $Short-\mathbb{C}^2$'s that are biholomorphically inequivalent and finally, we provide examples of $Short-\mathbb{C}^2$'s that are neither Reinhardt nor biholomorphic to Reinhardt domains.

math.DS↗

arXiv2018

Examples of non-autonomous basins of attraction-II

The aim of this article is to enlarge the list of examples of non-autonomous basins of attraction from our previous paper and at the same time explore some other properties that they satisfy. For instance, we show the existence of countably many disjoint Short $\mathbb{C}^k$'s in $\mathbb{C}^k.$ We also construct a Short $\mathbb{C}^k$ which is not Runge and exhibit yet another example whose boundary has Hausdorff dimension $2k.$

math.CV↗

arXiv2017

Examples of non-autonomous basins of attraction

The purpose of this paper is to present several examples of non--autonomous basins of attraction that arise from sequences of automorphisms of $\mathbb C^k$. In the first part, we prove that the non-autonomous basin of attraction arising from a pair of automorphisms of $\mathbb C^2$ of a prescribed form is biholomorphic to $\mathbb C^2$. This, in particular, provides a partial answer to a question raised in connection with Bedford's Conjecture about uniformizing stable manifolds. In the second part, we describe three examples of Short $\mathbb C^k$'s with specified properties. First, we show that for $k \geq 3$, there exist $(k-1)$ mutually disjoint Short $\mathbb C^k$'s in $\mathbb C^k$. Second, we construct a Short $\mathbb C^k$, large enough to accommodate a Fatou-Bieberbach domain, that avoids a given algebraic variety of codimension $2$. Lastly, we discuss examples of Short $\mathbb C^k$'s with (piece-wise) smooth boundaries.

math.CV↗

arXiv2015

Dynamics of semigroups of entire maps of $\mathbb{C}^k$

The goal of this paper is to study some basic properties of the Fatou and Julia sets for a family of holomorphic endomorphisms of $\mathbb{C}^k,\; k \ge 2$. We are particularly interested in studying these sets for semigroups generated by various classes of holomorphic endomorphisms of $\mathbb{C}^k,\; k \ge 2.$ We prove that if the Julia set of a semigroup $G$ which is generated by endomorphisms of maximal generic rank $k$ in $\mathbb{C}^k$ contains an isolated point, then $G$ must contain an element that is conjugate to an upper triangular automorphism of $\mathbb{C}^k.$ This generalizes a theorem of Fornaess-Sibony. Secondly, we define recurrent domains for semigroups and provide a description of such domains under some conditions.

math.DS↗

arXiv2013

Some aspects of shift-like automorphisms of C^k

The goal of this article is two fold. First, using transcendental shift-like automorphisms of C^k, k > 2 we construct two examples of non-degenerate entire mappings with prescribed ranges. The first example exhibits an entire mapping of C^k, k > 2 whose range avoids a given polydisc but contains the complement of a slightly larger concentric polydisc. This generalizes a result of Dixon-Esterle in C^2. The second example shows the existence of a Fatou--Bieberbach domain in C^k,k > 2 that is constrained to lie in a prescribed region. This is motivated by similar results of Buzzard and Rosay-Rudin. In the second part we compute the order and type of entire mappings that parametrize one dimensional unstable manifolds for shift-like polynomial automorphisms and show how they can be used to prove a Yoccoz type inequality for this class of automorphisms.

math.DS↗