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arXiv 1702.05995math.APmath-phmath.DGmath.MPmath.SP
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关于能量临界半波映射到$\mathbb{S}^2$

On energy-critical half-wave maps into $\mathbb{S}^2$

Enno Lenzmann, Armin Schikorra

摘要:

我们考虑能量临界半波映象方程$$\partial_t \mathbf{u} + \mathbf{u} \wedge |\nabla| \mathbf{u} = 0$$对于$\mathbf{u} : [0,T) \times \mathbb{R} \to \mathbb{S}^2$ .我们对所有能量有限的孤立波进行了完整的分类。证明是基于这些解决方案的最小曲面(不一定是自由的)边界上$\mathbb{S}^2$的几何特征。特别是,我们发现了一个明确的洛伦兹助推对称性,这是由共形莫比乌斯集团的目标$\mathbb{S}^2$适用于半调和映射从$\mathbb{R}$到$\mathbb{S}^2$。作为对分类结果的补充,我们对半调和映射$\mathbf{Q}$的线性化算子$L$进行了详细的分析,其中半调和映射具有任意次数$m \geq 1$。在这里,我们明确地确定零能量共振的零空间,特别是,我们证明了非简并的$\mathbf{Q}$。此外,我们给出了一个完整的描述$L$的频谱,找到它的所有$L^2$ -特征值,并证明其简单性。此外,我们证明了$L$和我们排除嵌入的本质谱内的特征值的一个估计。我们的谱分析是基于某些Jacobi算子(三对角无限矩阵)从一个共形变换的频谱问题上提出的$\mathbb{R}$单位圆$\mathbb{S}$的重新制定。最后,我们构造了一个酉映射,它可以被看作是一个规范变换,适合于未来的稳定性和爆破分析接近半调和映射。我们的谱结果也有潜在的应用到半调和映射热流,这是半波映射方程的抛物对应。

英文摘要:

We consider the energy-critical half-wave maps equation $$\partial_t \mathbf{u} + \mathbf{u} \wedge |\nabla| \mathbf{u} = 0$$ for $\mathbf{u} : [0,T) \times \mathbb{R} \to \mathbb{S}^2$. We give a complete classification of all traveling solitary waves with finite energy. The proof is based on a geometric characterization of these solutions as minimal surfaces with (not necessarily free) boundary on $\mathbb{S}^2$. In particular, we discover an explicit Lorentz boost symmetry, which is implemented by the conformal Möbius group on the target $\mathbb{S}^2$ applied to half-harmonic maps from $\mathbb{R}$ to $\mathbb{S}^2$. Complementing our classification result, we carry out a detailed analysis of the linearized operator $L$ around half-harmonic maps $\mathbf{Q}$ with arbitrary degree $m \geq 1$. Here we explicitly determine the nullspace including the zero-energy resonances; in particular, we prove the nondegeneracy of $\mathbf{Q}$. Moreover, we give a full description of the spectrum of $L$ by finding all its $L^2$-eigenvalues and proving their simplicity. Furthermore, we prove a coercivity estimate for $L$ and we rule out embedded eigenvalues inside the essential spectrum. Our spectral analysis is based on a reformulation in terms of certain Jacobi operators (tridiagonal infinite matrices) obtained from a conformal transformation of the spectral problem posed on $\mathbb{R}$ to the unit circle $\mathbb{S}$. Finally, we construct a unitary map which can be seen as a gauge transform tailored for a future stability and blowup analysis close to half-harmonic maps. Our spectral results also have potential applications to the half-harmonic map heat flow, which is the parabolic counterpart of the half-wave maps equation.

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