arXiv subjects

Sangdon Jin

Publications and source records attributed to Sangdon Jin.

10 recordsLinked to original sources

arXiv2024

Weighted isoperimetric ratios and extension problems for fractional conformal Laplacians

We investigate a novel connection between the weighted isoperimetric problems and the weighted Poisson integrals of the extension problems for nonlocal elliptic operators. We first derive sharp inequalities for the weighted Poisson integrals associated with degenerate elliptic equations on the half-space and the unit ball, and classify their extremizers. The equations arise from the Caffarelli-Silvestre extension for the fractional Laplacian on the Euclidean space and its conformal transformation via the Möbius transformation. We next interpret the above sharp inequalities in a conformal geometric viewpoint. For this aim, we formulate a variational problem involving a weighted isoperimetric ratio on a smooth metric measure space induced by a conformally compact Einstein (CCE) manifold. Then, we prove that the variational problem is closely linked to the Chang-González extension for a fractional conformal Laplacian on the conformal infinity of the CCE manifold, and is reduced to the sharp inequality if the CCE manifold is either the Poincaré half-space or ball model. We also find a criterion that ensures the existence of a smooth extremizer of the variational problem, and present a relevant conjecture.

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arXiv2024

Semiclassical equivalence of two white dwarf models as ground states of the relativistic Hartree-Fock and Vlasov-Poisson energies

We are concerned with the semi-classical limit for ground states of the relativistic Hartree-Fock energies (HF) under a mass constraint, which are considered as the quantum mean-field model of white dwarfs \cite{LeLe}. In Jang and Seok \cite{JS}, fermionic ground states of the relativistic Vlasov-Poisson energy (VP) are constructed as a classical mean-field model of white dwarfs, and are shown to be equivalent to the classical Chandrasekhar model. In this paper, we prove that as the reduced Planck constant $\hbar$ goes to the zero, the $\hbar$-parameter family of the ground energies and states of (HF) converges to the fermionic ground energy and state of (VP) with the same mass constraint.

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arXiv2022

Uniqueness and orbital stability of standing waves for the nonlinear Schrodinger equation with a partial confinement

We consider the 3d cubic nonlinear Schrödinger equation (NLS) with a strong 2d harmonic potential. The model is physically relevant to observe the lower-dimensional dynamics of the Bose-Einstein condensate, but its ground state cannot be constructed by the standard method due to its supercritical nature. In Bellazzini-Boussaïd-Jeanjean-Visciglia \cite{BBJV}, the authors constructed a proper ground state introducing a constrained energy minimization problem. In this paper, we further investigate the properties of the ground state. First, we show that as the partial confinement is increased, the 1d ground state is derived from the 3d energy minimizer with a precise rate of convergence. Then, by employing this dimension reduction limit, we prove the uniqueness of the 3d minimizer provided that the confinement is sufficiently strong. Consequently, we obtain the orbital stability of the minimizer, which improves that of the set of minimizers in the previous work \cite{BBJV}.

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arXiv2022

Coron's problem for the critical Lane-Emden system

In this paper, we address the solvability of the critical Lane-Emden system \[\begin{cases} -Δu=|v|^{p-1}v &\mbox{in } Ω_ε,\\ -Δv=|u|^{q-1}u &\mbox{in } Ω_ε,\\ u=v=0 &\mbox{on } \partial Ω_ε, \end{cases}\] where $N \ge 4$, $p \in (1,\frac{N-1}{N-2})$, $\frac{1}{p+1} + \frac{1}{q+1}=\frac{N-2}{N}$, and $Ω_ε$ is a smooth bounded domain with a small hole of radius $ε> 0$. We prove that the system admits a family of positive solutions that concentrate around the center of the hole as $ε\to 0$, obtaining a concrete qualitative description of the solutions as well. To the best of our knowledge, this is the first existence result for the critical Lane-Emden system on a bounded domain, while the non-existence result on star-shaped bounded domains has been known since the early 1990s due to Mitidieri (1993) [30] and van der Vorst (1991) [36].

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arXiv2022

On steady states for the Vlasov-Schrödinger-Poisson system

The Vlasov-Schrödinger-Poisson system is a kinetic-quantum hybrid model describing quasi-lower dimensional electron gases. For this system, we construct a large class of 2D kinetic/1D quantum steady states in a bounded domain as generalized free energy minimizers, and we show their finite subband structure, monotonicity, uniqueness and conditional dynamical stability. Our proof is based on the concentration-compactness principle, but some additional difficulties arise due to lack of compactness originated from the hybrid nature (see Remark 1.9). To overcome the difficulties, we introduce a 3-step refinement of a minimizing sequence by rearrangement and partial minimization problems, and the coercivity lemma for the free energy (Lemma 5.3) is crucially employed.

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arXiv2022

On the nonlinear Schrödinger equation with a toroidal trap in the strong confinement regime

We consider the 3D cubic nonlinear Schrödinger equation (NLS) with a strong toroidal trap. In the first part, we show that as the confinement is strengthened, a large class of global solutions to the time-dependent model can be described by 1D flows solving the 1D periodic NLS (Theorem 1.4). In the second part, we construct a steady state as a constrained energy minimizer, and prove its dimension reduction to the well-known 1D periodic ground state (Theorem 1.6 and 1.7). Then, employing the dimension reduction limit, we establish the local uniqueness and the orbital stability of the 3D ring soliton (Theorem 1.8). These results justify the emergence of stable quasi-1D periodic dynamics for Bose-Einstein condensates on a ring in physics experiments.

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arXiv2021

Solitary waves for the nonlinear Schrödinger-Poisson system with positron-electron interaction

In this paper, we study the existence of positive solutions to the nonlinear elliptic system, which is derived from taking the nonrelativistic limit of the nonlinear Maxwell-Klein-Gordon equations under the decomposition of waves functions into positron and electron parts. We characterize the existence and nonexistence of positive vector solutions, depending on parameters $p$ and $μ_{ij}$.

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arXiv2021

Orbital stability for the mass-critical and supercritical pseudo-relativistic nonlinear Schrodinger equation

For the one-dimensional mass-critical/supercritical pseudo-relativistic nonlinear Schrodinger equation, a stationary solution can be constructed as an energy minimizer under an additional kinetic energy constraint and the set of energy minimizers is orbitally stable in \cite{BGV}. In this study, we proved the local uniqueness and established the orbital stability of the solitary wave by improving that of the energy minimizer set. A key aspect thereof is the reformulation of the variational problem in the non-relativistic regime, which we consider to be more natural because the proof extensively relies on the subcritical nature of the limiting model. Thus, the role of the additional constraint is clarified, a more suitable Gagliardo-Nirenberg inequality is introduced, and the non-relativistic limit is proved. Subsequently, this limit is employed to derive the local uniqueness and orbital stability.

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arXiv2020

Nonrelativistic limit of solitary waves for nonlinear Maxwell-Klein-Gordon equations

We study the nonrelativistic limit of solitary waves from Nonlinear Maxwell-Klein-Gordon equations (NMKG) to Nonlinear Schrodinger-Poisson equations (NSP). It is known that the existence or multiplicity of positive solutions depends on the choices of parameters the equations contain. In this paper, we prove that for a given positive solitary wave of NSP, which is found in Ruiz's work \cite{R}, there corresponds a family of positive solitary waves of NMKG under the nonrelativistic limit. Notably, our results contain a new result of existence of positive solutions to (NMKG) with lower order nonlinearity.

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arXiv2020

Multi-bump standing waves for nonlinear Schrodinger equations with a general nonlinearity: the topological effect of potential wells

In this article, we are interested in multi-bump solutions of the singularly perturbed problem \begin{equation*} -ε^2Δv+V(x)v=f(v) \ \ \mbox{ in }\ \ \R^N. \end{equation*} Extending previous results \cite{B, DLY,W1}, we prove the existence of multi-bump solutions for an optimal class of nonlinearities $f$ satisfying the Berestycki-Lions conditions and, notably, also for more general classes of potential wells than those previously studied. We devise two novel topological arguments to deal with general classes of potential wells. Our results prove the existence of multi-bump solutions in which the centers of bumps converge toward potential wells as $ε\rightarrow 0$. Examples of potential wells include the following: the union of two compact smooth submanifolds of $\R^N$ where these two submanifolds meet at the origin and an embedded topological submanifold of $\R^N$.

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