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Chang-Shou Lin

Publications and source records attributed to Chang-Shou Lin.

At least 55 records · Page 3Linked to original sources
arXiv2017

Unitary monodromy implies the smoothness along the real axis for some Painlevé VI equation, I

In this paper, we study the Painlevé VI equation with parameter $(\frac {9}{8},\frac{-1}{8},\frac{1}{8},\frac{3}{8})$. We prove (i) An explicit formula to count the number of poles of an algebraic solution with the monodromy group $D_{N}$, where $D_{N}$ is the dihedral group of order $2N$. (ii) There are only four solutions without poles in $\mathbb{C}\backslash \left \{ 0,1\right \} $. (iii) If the monodromy group of the associated linear ODE of a solution $λ\left( t\right) $ is unitary, then $λ( t) $ has no poles in $\mathbb{R}% \backslash \{ 0,1\} $.

math.CA↗
arXiv2016

Toda systems and hypergeometric equations

This paper establishes certain existence and classification results for solutions to $SU(n)$ Toda systems with three singular sources at 0, 1, and $\infty$. First, we determine the necessary conditions for such an $SU(n)$ Toda system to be related to an $n$th order hypergeometric equation. Then, we construct solutions for $SU(n)$ Toda systems that satisfy the necessary conditions and also the interlacing conditions from Beukers and Heckman. Finally, for $SU(3)$ Toda systems satisfying the necessary conditions, we classify, under a natural reality assumption, that all the solutions are related to hypergeometric equations. This proof uses the Pohozaev identity.

math.AP↗
arXiv2016

Real-root property of the spectral polynomial of the Treibich-Verdier potential and related problems

We study the spectral polynomial of the Treibich-Verdier potential. Such spectral polynomial, which is a generalization of the classical Lame polynomial, plays fundamental roles in both the finite-gap theory and the ODE theory of Heun's equation. In this paper, we prove that all the roots of such spectral polynomial are real and distinct under some assumptions. The proof uses the classical concept of Sturm sequence and isomonodromic theories. We also prove an analogous result for a polynomial associated with a generalized Lame equation. Differently, our new approach is based on the viewpoint of the monodromy data.

math.CA↗
arXiv2016

Geometric quantities arising from bubbling analysis of mean field equations

Let $E = \Bbb C/Λ$ be a flat torus and $G$ be its Green function with singularity at $0$. Consider the multiple Green function $G_n$ on $E^n$: $$G_{n}(z_1,\cdots,z_n) := \sum_{i < j} G(z_{i} - z_{j}) - n \sum_{i = 1} ^{n} G(z_{i}).$$ A critical point $a = (a_1, \cdots, a_n)$ of $G_n$ is called trivial if $\{a_1, \cdots, a_n\} = \{-a_1, \cdots, -a_n\}$. For such a point $a$, two geometric quantities $D(a)$ and $H(a)$ arising from bubbling analysis of mean field equations are introduced. $D(a)$ is a global quantity measuring asymptotic expansion and $H(a)$ is the Hessian of $G_n$ at $a$. By way of geometry of Lamé curves developed in our previous paper (Cambridge J. Math 3, 2015), we derive precise formulas to relate these two quantities.

math.AP↗
arXiv2016

Mean field equations, hyperelliptic curves and modular forms: II

A pre-modular form $Z_n(σ; τ)$ of weight $\tfrac{1}{2} n(n + 1)$ is introduced for each $n \in \Bbb N$, where $(σ, τ) \in \Bbb C \times \Bbb H$, such that for $E_τ= \Bbb C/(\Bbb Z + \Bbb Z τ)$, every non-trivial zero of $Z_n(σ; τ)$, namely $σ\not\in E_τ[2]$, corresponds to a (scaling family of) solution to the mean field equation \begin{equation} \tag{MFE} \triangle u + e^u = ρ\, δ_0 \end{equation} on the flat torus $E_τ$ with singular strength $ρ= 8πn$. In Part I (Cambridge J. Math. 3, 2015), a hyperelliptic curve $\bar X_n(τ) \subset {\rm Sym}^n E_τ$, the Lamé curve, associated to the MFE was constructed. Our construction of $Z_n(σ; τ)$ relies on a detailed study on the correspondence $\Bbb P^1 \leftarrow \bar X_n(τ) \to E_τ$ induced from the hyperelliptic projection and the addition map. As an application of the explicit form of the weight 10 pre-modular form $Z_4(σ; τ)$, a counting formula for Lamé equations of degree $n = 4$ with finite monodromy is given in the appendix (by Y.-C. Chou).

math.AP↗
arXiv2015

Hamiltonian system for the elliptic form of Painlevé VI equation

In literature, it is known that any solution of Painlevé VI equation governs the isomonodromic deformation of a second order linear Fuchsian ODE on $\mathbb{CP}^{1}$. In this paper, we extend this isomonodromy theory on $\mathbb{CP}^{1}$ to the moduli space of elliptic curves by studying the isomonodromic deformation of the generalized Lamé equation. Among other things, we prove that the isomonodromic equation is a new Hamiltonian system, which is equivalent to the elliptic form of Painlevé VI equation for generic parameters. For Painlevé VI equation with some special parameters, the isomonodromy theory of the generalized Lamé equation greatly simplifies the computation of the monodromy group in $\mathbb{CP}^{1}$. This is one of the advantages of the elliptic form.

math.AG↗
arXiv2015

Local profile of fully bubbling solutions to SU(n+1) Toda Systems

In this article we prove that for locally defined singular SU(n+1) Toda systems in R^2, the profile of fully bubbling solutions near the singular source can be accurately approximated by global solutions. The main ingredients of our new approach are the classification theorem of Lin-Wei-Ye and the non-degeneracy of the linearized Toda system, which make us overcome the difficulties that come from the lack of symmetry and the singular source.

math.AP↗
arXiv2015

Resolution of Chern--Simons--Higgs Vortex Equations

It is well known that the presence of multiple constraints of non-Abelian relativisitic Chern--Simons--Higgs vortex equations makes it difficult to develop an existence theory when the underlying Cartan matrix $K$ of the equations is that of a general simple Lie algebra and the strongest result in the literature so far is when the Cartan subalgebra is of dimension 2. In this paper we overcome this difficulty by implicitly resolving the multiple constraints using a degree-theorem argument, utilizing a key positivity property of the inverse of the Cartan matrix deduced in an earlier work of Lusztig and Tits, which enables a process that converts the equality constraints to inequality constraints in the variational formalism. Thus this work establishes a general existence theorem which settles a long-standing open problem in the field regarding the general solvability of the equations.

math-ph↗
arXiv2015

Mean field equations, hyperelliptic curves and modular forms: I

We develop a theory connecting the following three areas: (a) the mean field equation (MFE) $\triangle u + e^u = ρ\, δ_0$, $ρ\in \mathbb R_{>0}$ on flat tori $E_τ= \mathbb C/(\mathbb Z + \mathbb Zτ)$, (b) the classical Lamé equations and (c) modular forms. A major theme in part I is a classification of developing maps $f$ attached to solutions $u$ of the mean field equation according to the type of transformation laws (or monodromy) with respect to $Λ$ satisfied by $f$. We are especially interested in the case when the parameter $ρ$ in the mean field equation is an integer multiple of $4π$. In the case when $ρ= 4π(2n + 1)$ for a non-negative integer $n$, we prove that the number of solutions is $n + 1$ except for a finite number of conformal isomorphism classes of flat tori, and we give a family of polynomials which characterizes the developing maps for solutions of mean field equations through the configuration of their zeros and poles. Modular forms appear naturally already in the simplest situation when $\,ρ=4π$. In the case when $ρ= 8πn$ for a positive integer $n$, the solvability of the MFE depends on the \emph{moduli} of the flat tori $E_τ$ and leads naturally to a hyperelliptic curve $\bar X_n=\bar X_{n}(τ)$ arising from the Hermite-Halphen ansatz solutions of Lamé's differential equation $\frac{d^2 w}{dz^2}-(n(n+1)\wp(z;Λ_τ) + B) w=0$. We analyse the curve $\bar X_n$ from both the analytic and the algebraic perspective, including its local coordinate near the point at infinity, which turns out to be a smooth point of $\bar{X}_n$. We also specify the role of the branch points of the hyperelliptic projection $\bar X_n \to \mathbb P^1$ when the parameter $ρ$ varies in a neighborhood of $ρ= 8πn$.

math.AP↗
arXiv2014

Uniqueness of topological solutions of self-dual Chern-Simons equation with collapsing vortices

We consider the following Chern-Simons equation, \begin{equation} \label{0.1} Δu+\frac 1{\varepsilon^2} e^u(1-e^u)=4π\sum_{i=1}^N δ_{p_i^\varepsilon},\quad \text{in}\quad Ω, \end{equation} where $Ω$ is a 2-dimensional flat torus, $\varepsilon>0$ is a coupling parameter and $δ_p$ stands for the Dirac measure concentrated at $p$. In this paper, we proved that the topological solutions of \eqref{0.1} are uniquely determined by the location of their vortices provided the coupling parameter $\varepsilon$ is small and the collapsing velocity of vortices $p_i^\varepsilon$ is slow enough or fast enough comparing with $\varepsilon$. This extends the uniqueness results of Choe \cite{Choe2005} and Tarantello \cite{Tarantello2007}. Meanwhile, for any topological solution $ψ$ defined in $\mathbb R^2$ whose linearized operator is non-degenerate, we construct a sequence topological solutions $u_\varepsilon$ of \eqref{0.1} whose asymptotic limit is exactly $ψ$ after rescaling around $0$. A consequence is that non-uniqueness of topological solutions in $\mathbb R^2$ implies non-uniqueness of topological solutions on torus with collapsing vortices.

math.AP↗
arXiv2014

Infinitely many sign-changing and semi-nodal solutions for a nonlinear Schrodinger system

We study the following coupled Schrödinger equations which have appeared as several models from mathematical physics: {displaymath} {cases}-Δu_1 +\la_1 u_1 = μ_1 u_1^3+βu_1 u_2^2, \quad x\in Ω, -Δu_2 +\la_2 u_2 =μ_2 u_2^3+βu_1^2 u_2, \quad x\in \Om, u_1=u_2=0 \,\,\,\hbox{on \,$\partial\Om$}.{cases}{displaymath} Here $\Om$ is a smooth bounded domain in $\R^N (N=2, 3)$ or $\Om=\RN$, $\la_1,\, \la_2$, $μ_1,\,μ_2$ are all positive constants and the coupling constant $\bb<0$. We show that this system has infinitely many sign-changing solutions. We also obtain infinitely many semi-nodal solutions in the following sense: one component changes sign and the other one is positive. The crucial idea of our proof, which has never been used for this system before, is turning to study a new problem with two constraints. Finally, when $\Om$ is a bounded domain, we show that this system has a least energy sign-changing solution, both two components of which have exactly two nodal domains, and we also study the asymptotic behavior of solutions as $β\to -\infty$ and phase separation is expected.

math.AP↗
arXiv2014

Uniqueness of topological multi-vortex solutions for a skew-symmetric Chern-Simons system

Consider the following skew-symmetric Chern-Simons system \begin{equation*}\left \{ \begin{split} &Δu_{1}+\frac{1}{\varepsilon^2} e^{u_{2}}(1-e^{u_{1}})=4π\sum^{N_1}_{j=1}δ_{p_{j,1}}\\ &Δu_{2}+\frac{1}{\varepsilon^2} e^{u_{1}}(1-e^{u_{2}})=4π\sum^{N_2}_{j=1}δ_{p_{j,2}} \end{split}\right.\quad\text{ in }\quadΩ, \end{equation*} where $Ω$ is a flat 2-dimensional torus $\mathbb{T}^2$ or $\mathbb{R}^2$, $\varepsilon> 0$ is a coupling parameter, and $δ_p$ denotes the Dirac measure concentrated at $p$. In this paper, we prove that, when the coupling parameter $\varepsilon$ is small, the topological type solutions to the above system are uniquely determined by the location of their vortex points. This result follows by the bubbling analysis and the non-degency of linearized equations.

math.AP↗
arXiv2014

Degree counting and shadow system for $SU(3)$ Toda system: one bubbling

Here we initiate the program for computing the Leray-Schauder topological degree for $SU(3)$ Toda system. This program still contains a lot of challenging problems for analysts. The first step of our approach is to answer whether concentration phenomena holds or not. In this paper, we prove the concentration phenomena holds while $ρ_1$ crosses $4π$, and $ρ_2\notin 4π\mathbb{N}$. However, for $ρ_1\geq 8π$, the question whether concentration holds or not still remains open up to now. The second step is to study the corresponding shadow system and its degree counting formula. The last step is to construct bubbling solution of $SU(3)$ Toda system via a non-degenerate solution of the shadow system. Using this construction, we succeed to calculate the degree for $ρ_1\in(0,4π)\cup(4π,8π)$ and $ρ_2\notin 4π\mathbb{N}$.

math.AP↗
arXiv2014

Removable singularity of positive solutions for a critical elliptic system with isolated singularity

We study qualitative properties of positive singular solutions to a two-coupled elliptic system with critical exponents. This system is related to coupled nonlinear Schrodinger equations with critical exponents for nonlinear optics and Bose-Einstein condensates. We prove a sharp result on the removability of the same isolated singularity for both two components of the solutions. We also prove the nonexistence of positive solutions with one component bounded near the singularity and the other component unbounded near the singularity. These results will be applied in a subsequent work where the same system in a punctured ball will be studied.

math.AP↗
arXiv2014

On Non-topological Solutions of the ${\bf G}_2$ Chern-Simons System

For any rank 2 of simple Lie algebra, the relativistic Chern-Simons system has the following form: \begin{equation}\label{e001} \left\{\begin{array}{c} Δu_1+(\sum_{i=1}^2K_{1i}e^{u_i} -\sum_{i=1}^2\sum_{j=1}^2e^{u_i}K_{1i}e^{u_j}K_{ij})=4π\displaystyle \sum_{j=1}^{N_1}δ_{p_j}\\ Δu_2+ (\sum_{i=1}^2K_{2i}e^{u_i}-\sum_{i=1}^2\sum_{j=1}^2e^{u_i}K_{2i}e^{u_j}K_{ij})=4π\displaystyle \sum_{j=1}^{N_2}δ_{q_j} \end{array} \right.\mbox{in}\; \mathbb{R}^2, \end{equation} where $K$ is the Cartan matrix of rank $2$. There are three Cartan matrix of rank 2: ${\bf A}_2$, ${\bf B}_2$ and ${\bf G}_2$. A long-standing open problem for \eqref{e001} is the question of the existence of non-topological solutions. In a previous paper \cite{ALW}, we have proven the existence of non-topological solutions for the ${\bf A}_2$ and ${\bf B}_2$ Chern-Simons system. In this paper, we continue to consider the ${\bf G}_2$ case. We prove the existence of non-topological solutions under the condition that either $N_2\displaystyle\sum_{j=1}^{N_1} p_j=N_1\displaystyle \sum_{j=1}^{N_2} q_j $ or $N_2\displaystyle\sum_{j=1}^{N_1}p_j \not =N_1\displaystyle \sum_{j=1}^{N_2} q_j$ and $N_1,N_2>1$, $ |N_1-N_2|\neq 1$. We solve this problem by a perturbation from the corresponding ${\bf G}_2$ Toda system with one singular source. Combining with \cite{ALW}, we have proved the existence of non-topological solutions to the Chern-Simons system with Cartan matrix of rank $2$.

math.AP↗
arXiv2014

Isomonodromy aspects of the tt* equations of Cecotti and Vafa I. Stokes data

We describe all smooth solutions of the two-function tt*-Toda equations (a version of the tt* equations, or equations for harmonic maps into SL(n,R)/SO(n)) in terms of (i) asymptotic data, (ii) holomorphic data, and (iii) monodromy data. This allows us to find all solutions with integral Stokes data. These include solutions associated to nonlinear sigma models (quantum cohomology) or Landau-Ginzburg models (unfoldings of singularities), as conjectured by Cecotti and Vafa.

math.DG↗
arXiv2014

Existence of non-topological solutions for a skew-symmetric Chern-Simons system

We investigate the existence of non-topological solutions $(u_1,u_2)$ satisfying $$u_{i}(x)=-2β_i\ln|x|+O(1),\quad\text{as }|x|\rightarrow +\infty,$$ such that $β_i>1$ and $$(β_1-1)(β_2-1)>(N_1+1)(N_2+1),$$ for a skew-symmetric Chern-Simons system. By the bubbling analysis and the Leray-Schauder degree theory, we get the existence results except for a finite set of curves: $$\frac{N_1}{β_1+N_1}+\frac{N_2}{β_2+N_2}=\frac{k-1}{k},k=2,\cdots,\max(N_1,N_2).$$ This generalizes a previous work by Choe-Kim-Lin \cite{ChoeKimLin2011}.

math.AP↗