Konstantinos Bampouras

activity

20232026

collaborators

10 papers

math.CV2026

Failure of Nehari's Theorem for Multiplicative Hankel Forms in Schatten Classes II

Konstantinos Bampouras

We prove that for any $p > 4$ we can find a Schatten class Hankel operator $\Ha_ϕ$ defined on the Hardy space of the infinite torus $H^{2} (T^{\infty})$ that belongs to the Schat…

math.FA2026

Helson Inequality, Hankel Operators, and Weak Factorization on Paley-Wiener spaces of Convex Domains

Konstantinos Bampouras

For any convex set $Ω \subset R^{n}$ that does not contain affine lines, we prove the inequality $$\int_Ω\frac{|\hat{f}(x)|^2}{ω_Ω(x)}\,dx\leq C(n)\|f\|_{L^1}^2,\quad \supp\ha…

math.CA2026

Boundary-Weighted Fourier Inequalities for Convex Domains

Konstantinos Bampouras, Karl-Mikael Perfekt

We consider the natural family of Fourier inequalities for the Paley--Wiener space $PW^{q} (Ω)$ , consisting of $L^{q}$ -functions with Fourier support in a convex set $Ω\subset…

math.CV2026

The norm of the backward shift on $H^{4}$ is $4 φ$

Konstantinos Bampouras, Adrián Llinares

We prove that the backward shift operator on $H^{4}$ has norm equal to $4 φ$ , with $φ = \frac{1 + 5}{2}$ . Furthermore, we characterize all extremal functions; they are pr…

math.FA2026

Recovering Product BMO from Schatten Hankel operators

Konstantinos Bampouras, Karl-Mikael Perfekt

We prove that if a small Hankel operator on the product Hardy space belongs to some Schatten class $S^{p}$ , $p < \infty$ , then it has a symbol in product BMO. In other words, the con…

math.FA2025

Nehari's Theorem and Hardy's inequality for Paley--Wiener spaces

Konstantinos Bampouras

Recently it was proven that for a convex subset of $R^{n}$ that has infinitely many extreme vectors, the Nehari theorem fails, that is, there exists a bounded Hankel opera…

math.CV2025

Inner Functions, Möbius Distortion and Angular Derivatives

Konstantinos Bampouras, Artur Nicolau

We prove that an inner function has finite $L (p)$ -entropy if and only if its accumulated Möbius distortion is in $L^{p}$ , $0 < p < \infty$ . We also study the support of the po…

math.FA2024

Besov spaces and Schatten class Hankel operators for Hardy and Paley--Wiener spaces in higher dimensions

Konstantinos Bampouras, Karl-Mikael Perfekt

We consider Schatten class membership of Hankel operators on Paley--Wiener spaces of convex $Ω \subset R^{n}$ , both for bounded and unbounded domains. In particular, the clas…

math.FA2023

Norm attaining vectors and Hilbert points

Konstantinos Bampouras, Ole Fredrik Brevig

Let $H$ be a Hilbert space that can be embedded as a dense subspace of a Banach space $X$ such that the norm of the embedding is equal to $1$ . We consider the following statements…

math.FA2023

On the failure of the Nehari Theorem for Paley-Wiener spaces

Konstantinos Bampouras

Let $Ω$ be a nonempty, open and convex subset of $R^{n}$ . The Paley-Wiener space with respect to $Ω$ is defined to be the closed subspace of $L^{2} (R^{n})$ of fun…

Failure of Nehari's Theorem for Multiplicative Hankel Forms in Schatten Classes II

Helson Inequality, Hankel Operators, and Weak Factorization on Paley-Wiener spaces of Convex Domains

Boundary-Weighted Fourier Inequalities for Convex Domains

The norm of the backward shift on H4 is 4φ​

Recovering Product BMO from Schatten Hankel operators

Nehari's Theorem and Hardy's inequality for Paley--Wiener spaces

Inner Functions, Möbius Distortion and Angular Derivatives

Besov spaces and Schatten class Hankel operators for Hardy and Paley--Wiener spaces in higher dimensions

Norm attaining vectors and Hilbert points

On the failure of the Nehari Theorem for Paley-Wiener spaces

The norm of the backward shift on $H^{4}$ is $4 φ$