arXiv subjects

Beomjong Kwak

Publications and source records attributed to Beomjong Kwak.

5 recordsLinked to original sources

arXiv2026

A universal bound on the blow-up rate for the focusing mass-critical nonlinear Schr\"odinger equation

In this paper, we investigate a universal blow-up bound for the focusing mass-critical nonlinear Schr\"odinger equation for general initial data in $L^2(\mathbb R^d)$, extending previous knowledge for mass near the ground-state threshold due to Merle and Rapha\"el. The main results are twofold. First, we show the nonexistence of self-similar rate blow-up solutions. Second, under radial symmetry, we establish the sharp log--log correction to the self-similar bound on the blow-up rate. The proofs are based on a new analysis of general blow-up solutions, which does not rely on any ansatz or variational structure.

math.AP↗

arXiv2025

Global well-posedness of the cubic nonlinear Schr\"odinger equation on $\mathbb{T}^{2}$

We prove global well-posedness for the cubic nonlinear Schr\"odinger equation for periodic initial data in the mass-critical dimension $d=2$ for initial data of arbitrary size in the defocusing case and data below the ground state threshold in the focusing case. The result is based on a new inverse Strichartz inequality, which is proved by using incidence geometry and additive combinatorics, in particular, the inverse theorems for Gowers uniformity norms by Green-Tao-Ziegler. This allows to transfer the analogous results of Dodson for the non-periodic mass-critical NLS to the periodic setting. In addition, we construct an approximate periodic solution which implies sharpness of the results.

math.AP↗

arXiv2024

Global well-posedness of the energy-critical nonlinear Schr\"odinger equations on $\mathbb{T}^{d}$

In this paper, we prove the global well-posedness of the energy-critical nonlinear Schr\"odinger equations on the torus $\mathbb{T}^{d}$ for general dimensions. This result is new for dimensions $d\ge5$, extending previous results for $d=3,4$ [10,22]. Compared to the cases $d=3,4$, the regularity theory for higher $d$, developed in the underlying local well-posedness result [17], is less understood. In particular, stability theory and inverse inequalities, which are ingredients in [10,22] and more generally in the widely used concentration compactness framework since [13], are too weak to be applied to higher dimensions. Our proof introduces a new strategy for addressing global well-posedness problems. Without relying on perturbation theory, we develop tools to analyze the concentration dynamics of the nonlinear flow. On the way, we show the formation of a nontrivial concentration.

math.AP↗

arXiv2024

Critical local well-posedness of the nonlinear Schr\"odinger equation on the torus

In this paper, we study the local well-posedness of nonlinear Schr\"odinger equations on tori $\mathbb{T}^{d}$ at the critical regularity. We focus on cases where the nonlinearity $|u|^{a}u$ is non-algebraic with small $a>0$. We prove the local well-posedness for a wide range covering the mass-supercritical regime. Moreover, we supplementarily investigate the regularity of the solution map. In pursuit of lowering $a$, we prove a bilinear estimate for the Schr\"odinger operator on tori $\mathbb{T}^{d}$, which enhances previously known multilinear estimates. We design a function space adapted to the new bilinear estimate and a package of Strichartz estimates, which is not based on conventional atomic spaces.

math.AP↗

arXiv2023

Strichartz estimates and global well-posedness of the cubic NLS on $\mathbb{T}^{2}$

The optimal $L^4$-Strichartz estimate for the Schr{\"o}dinger equation on the two-dimensional rational torus $\mathbb{T}^2$ is proved, which improves an estimate of Bourgain. A new method based on incidence geometry is used. The approach yields a stronger $L^4$ bound on a logarithmic time scale, which implies global existence of solutions to the cubic (mass-critical) nonlinear Schr\"odinger equation in $H^s(\mathbb{T}^2)$ for any $s>0$ and data which is small in the critical norm.

math.AP↗