Boundary regularity for manifold constrained $p(x)$-harmonic maps

凸环中从p-调和势到∞-调和势的正则性

Regularity from $p$-harmonic potentials to $\infty$-harmonic potentials in convex rings

本文在任意凸环域中研究从p-调和势到∞-调和势的正则性，证明了∞-调和势的内部C^1正则性及部分Sobolev正则性。

C^1-Regularity of planar \infty-harmonic functions - REVISIT

In the seminal paper [Arch. Ration. Mech. Anal. 176 (2005), 351--361], Savin proved the $C^1$-regularity of planar $\infty$-harmonic functions $u$. Here we give a new understanding of it from a capacity viewpoint and drop several high technique arguments therein. Our argument is essentially based on a topological lemma of Savin, a flat estimate by Evans and Smart, % \cite{es11a}, $W^{1,2}_{loc}$-regularity of $|Du|$ and Crandall's flow for infinity harmonic functions.

On the $C^{1,α}$ Regularity of $p$-Harmonic Functions in the Heisenberg Group

We present a proof of the local Hölder regularity of the horizontal derivatives of weak solutions to the $p$-Laplace equation in the Heisenberg group $\mathbb{H}^1$ for $p>4 $.

Boundary regularity for $p$-harmonic functions and solutions of obstacle problems on unbounded sets in metric spaces

The theory of boundary regularity for $p$-harmonic functions is extended to unbounded open sets in complete metric spaces with a doubling measure supporting a $p$-Poincaré inequality, $1<p<\infty$. The barrier classification of regular boundary points is established, and it is shown that regularity is a local property of the boundary. We also obtain boundary regularity results for solutions of the obstacle problem on open sets, and characterize regularity further in several other ways.

Partial regularity for manifold constrained p(x)-harmonic maps

We prove that manifold constrained $p(x)$-harmonic maps are $C^{1,β}$-regular outside a set of zero $n$-dimensional Lebesgue's measure, for some $β\in (0,1)$. We also provide an estimate from above of the Hausdorff dimension of the singular set.

Regularity and Uniqueness of p-harmonic Maps with Small Range

We prove the uniqueness of solutions to Dirichlet problem for p-harmonic maps with images in a small geodesic ball of the target manifold. As a consequence, we show that such maps have Hoelder continuous derivatives. This gives an extension of a result by S. Hildebrandt et al concerning harmonic maps.

$HW^{2,2}_{\rm loc}$-regularity for $p$-harmonic functions in Heisenberg groups

Let $1<p\le4$ when $n=1$ and $1<p< 3+\frac{1}{n-1} $ when $n\ge2$. We obtain the second-order horizontal Sobolev $HW^{2,2}_{\rm loc} $-regularity of $p$-harmonic functions in the Heisenberg group $\mathbb H^n$. This improves the known range of $p$ obtained by Domokos and Manfredi in 2005.

3-Commutators Estimates and the Regularity of 1/2 Harmonic Maps into Spheres

We prove the regularity of weak 1/2-harmonic maps from the real line into a sphere. The key point in our result is first a formulation of the 1/2-harmonic map equation in the form of a non-local linear Schrödinger type equation with a 3-terms commutators in the right-hand-side . We then establish a sharp estimate for these 3-commutators.

Uniqueness and Regularity of the Fractional Harmonic Gradient Flow in $S^{n-1}$

In this paper, we study the fractional harmonic gradient flow on $S^1$ taking values in $S^{n-1} \subset \mathbb{R}^n$ for every $n \geq 2$, in particular addressing uniqueness and regularity of solutions in the so-called energy class with sufficiently small energy, adding to the existing body of knowledge which includes existence of solutions and certain bubbling phenomena.

Regularity issues for Cosserat continua and $p$-harmonic maps

For minimizers in a geometrically nonlinear Cosserat model for micropolar elasticity of continua, we prove interior Hölder regularity, up to isolated singular points that may be possible if the exponent $p$ from the model is $2$ or in $(\frac{32}{15},3)$. The obstacle to full continuity turns out to be the existence of certain minimizing homogeneous $p$-harmonic maps to $S^3$. For those, we slightly improve existing regularity theorems in order to achieve our result on the Cosserat model.

Global second order Sobolev-regularity of $p$-harmonic functions

We prove a global version of the classical result that $p$-harmonic functions belong to $W^{2,2}_{loc}$ for $1<p<3+\frac{2}{n-2}$. The proof relies on Cordes' matrix inequalities [7] and techniques from the work of Cianchi and Maz'ya [5,6].

调和映照到球面在奇异或退化自由边界处的部分正则性

Partial Regularity for Harmonic Maps into Spheres at a Singular or Degenerate Free Boundary

本文证明了在域度量沿自由边界以$d^α$速率退化或奇异时，具有自由边界数据的弱平稳调和映照的部分正则性。

$\mathcal{A}$-harmonic approximation and partial regularity, revisited

We give a direct harmonic approximation lemma for local minima of quasiconvex multiple integrals that entails their $\mathrm{C}^{1,α}$ or $\mathrm{C}^{\infty}$-partial regularity. Different from previous contributions, the method is fully direct and elementary, only hinging on the $\mathrm{L}^{p}$-theory for strongly elliptic linear systems and Sobolev's embedding theorem. Especially, no heavier tools such as Lipschitz truncations are required.

极小化内蕴分数阶调和映射的定量正则性

Quantitative regularity for minimizing intrinsic fractional harmonic maps

本文研究极小化内蕴分数阶调和映射，结合修正Luckhaus引理与定量分层理论证明紧性、奇异集体积估计及改进的维数界。

极小调和映射正则性理论简介

A brief introduction to the regularity theory of minimising harmonic maps

本文综述极小调和映射正则性理论的核心结果，涵盖变分、正则性定理、爆破与奇异集分析，并延伸至平稳情形及近期进展。

n/p-Harmonic maps: regularity for the sphere case

We introduce n/p-harmonic maps as critical points of E(v) the Lp-Norm of the alpha-laplacian of v, where pointwise v maps Rn into a sphere, and alpha = n/p. This energy combines the non-local behaviour of the fractional harmonic maps introduced by Riviere and the first author with the degenerate arguments of the n-laplacian. In this setting, we will prove Holder continuity.

Partial regularity of harmonic maps from a Riemannian manifold into a Lorentzian manifold

In this paper, we will study the partial regularity theorem for stationary harmonic maps from a Riemannian manifold into a Lorentzian manifold. For a weakly stationary harmonic map $(u,v)$ from a smooth bounded open domain $Ω\subset\R^m$ to a Lorentzian manifold with Dirichlet boundary condition, we prove that it is smooth outside a closed set whose $(m-2)$-dimension Hausdorff measure is zero. Moreover, if the target manifold $N$ does not admit any harmonic sphere $S^l$, $l=2,...,m-1$, we will show $(u,v)$ is smooth.

平稳二值调和函数的正则性理论

A Regularity Theory for Stationary Two-valued Harmonic Functions

本文研究平稳二值调和函数的正则性，利用 Almgren 单调性公式和爆破方法证明其 Lipschitz 连续性，并刻画节点集的解析结构，可用于分离模型极限问题。

球值分数阶调和映射的全局正则性理论

A global regularity theory for shpere-valued fractional harmonic maps

本文针对球值分数阶调和映射，利用 Cheeger-Naber 定量微分方法建立奇异集的定量分层理论，从而获得全局正则性估计。

Existence, Uniqueness and Regularity of the Fractional Harmonic Gradient Flow in General Target Manifolds

In this paper, we continue to study the fractional harmonic gradient flow on $S^{n-1}$ taking values in a general closed manifold $N \subset \mathbb{R}^n$, addressing global existence and uniqueness of solutions of energy class with sufficiently small energy, adding to the existing body of knowledge pertaining to the half-harmonic gradient flow and expanding upon our previous work in [34]. We extend the techniques by Struwe in [30] and Rivière in [22] to the non-local framework analogous to [34] to derive uniqueness, employ commutator estimates as in [8] for regularity and follow [30] for a ge…

Elliptic regularity theory applied to time harmonic anisotropic Maxwell's equations with less than Lipschitz complex coefficients

The focus of this paper is the study of the regularity properties of the time harmonic Maxwell's equations with anisotropic complex coefficients, in a bounded domain with $C^{1,1}$ boundary. We assume that at least one of the material parameters is $W^{1,3+δ}$ for some $δ>0$. Using regularity theory for second order elliptic partial differential equations, we derive $W^{1,p}$ estimates and Hölder estimates for electric and magnetic fields up to the boundary. We also derive interior estimates in bi-anisotropic media.

具有 Hölder 及各类低于 Hölder 连续系数的时谐 Maxwell 系统解的正则性

Regularity of solutions to time-harmonic Maxwell's system with Hölder and various lower than Hölder continuous coefficients

本文为二阶线性椭圆方程与时谐 Maxwell 系统建立完整 Schauder 理论，并在 Hölder 连续系数下证明时谐各向异性 Maxwell 方程解的全局 Hölder 正则性，将 Hölder 指数提升至 (0,1)。

An asymtotic sharp Sobolev regularity for planar infinity harmonic functions

Given an arbitrary planar $\infty$-harmonic function $u$, for each $α>0$ we establish a quantitative local $W^{1,2}$-estimate of $|Du|^α$, which is sharp as $α\to0$. We also show that the distributional determinant of $u$ is a Radon measure enjoying some quantitative lower and upper bounds. As a by-product, for each $p>2$ we obtain some quantitative local $W^{1,p}$-estimates of $u$, and consequently, an $L^p$-Liouville property for $\infty$-harmonic functions in whole plane.

Epsilon-regularity for p-harmonic maps at a free boundary on a sphere

We prove an $ε$-regularity theorem for vector-valued p-harmonic maps, which are critical with respect to a partially free boundary condition, namely that they map the boundary into a round sphere. This does not seem to follow from the reflection method that Scheven used for harmonic maps with free boundary (i.e., the case $p=2$): the reflected equation can be interpreted as a $p$-harmonic map equation into a manifold, but the regularity theory for such equations is only known for round targets. Instead, we follow the spirit of the last-named author's recent work on free boundary harmonic maps …

On regularity theory for n/p-harmonic maps into manifolds

In this paper we continue the investigation of the regularity of the so-called weak $\frac{n}{p}$-harmonic maps in the critical case. These are critical points of the following nonlocal energy \[ {\mathcal{L}}_s(u)=\int_{\mathbb{R}^n}| ( {-Δ})^{\frac{s}{2}} u(x)|^p dx\,, \] where $u\in \dot{H}^{s,p}(\mathbb{R}^n,\mathcal{N})$ and ${\mathcal{N}}\subset\mathbb{R}^N$ is a closed $k$ dimensional smooth manifold and $s=\frac{n}{p}$. We prove Hölder continuity for such critical points for $p \leq 2$. For $p > 2$ we obtain the same under an additional Lorentz-space assumption. The regularity theory i…

Regularity for solutions of H-systems and n-harmonic maps with n/2 square integrable derivatives

We study the regularity of weak solutions for two elliptic systems involving the $n$-Laplacian and a critical nonlinearity in the right hand side: $H$-systems and $n$-harmonic maps into compact Riemannian manifolds. Under the assumptions that the solutions belong to $W^{n/2,2}$ in an even dimension $n$, we prove their continuty. The tools used in the proof involve Hardy spaces and BMO, and the Rivière--Uhlenbeck decomposition (with estimates in Morrey spaces). A prominent role is played by the Coifman--Rochberg--Weiss commutator theorem.

分数调和映射的细密正则性及其应用

Fine regularity of fractional harmonic maps and applications

本文研究分数调和映射的正则性问题，通过非局部方程理论改进了已知结果，并应用于具有自由边界的调和映射及热流的可微性研究。

Partial regularity of $p(x)$-harmonic maps

Let $(g^{αβ}(x))$ and $(h_{ij}(u))$ be uniformly elliptic symmetric matrices, and assume that $h_{ij}(u)$ and $p(x) \, (\, \geq 2)$ are sufficiently smooth. We prove partial regularity of minimizers for the functional [ {\mathcal F}(u) = \int_Ω(g^{αβ}(x) h_{ij}(u) D_αu^iD_βu^j)^{p(x)/2} dx, \] under the non-standard growth conditions of $p(x)$-type. If $g^{αβ}(x)$ are in the class $VMO$, we have partial Hölder regularity. Moreover, if $g^{αβ}$ are Hölder continuous, we can show partial $C^{1,α}$-regularity.

分数阶 $p$-调和函数的 $C^{1+α}$ 正则性

$C^{1+α}$ regularity for fractional $p$-harmonic functions

该研究证明了当 $p$ 位于 $[2,2/(1-s))$ 时，分数阶 $p$-Laplace 方程的解具有内部 $C^{1,α}$ 正则性。

Interior and Boundary-Regularity for Fractional Harmonic Maps on Domains

We prove continuity on domains up to the boundary for n/2-polyharmonic maps into manifolds. Technically, we show how to adapt Helein's direct approach to the fractional setting. This extends a remark by the author that this is possible in the setting of Riviere's famous regularity result for critical points of conformally invariant variational functionals. Moreover, pointwise behavior for the involved three-commutators is established. Continuity up to the boundary is then obtained via an adaption of Hildebrandt and Kaul's technique to the non-local setting.

$(s,p)$-调和函数的梯度正则性

Gradient regularity for $(s,p)$-harmonic functions

本文研究$(s,p)$-调和函数的局部正则性，证明其弱可微、弱梯度任意阶局部可积，并得到任意Hölder连续性及分数阶可微性，且估计在$s\to1$时稳定并恢复$p$-调和函数的已知正则性。

Regularity for harmonic maps into certain Pseudo-Riemannian manifolds

In this article, we investigate the regularity for certain elliptic systems without a $L^2$-antisymmetric structure. As applications, we prove some $ε$-regularity theorems for weakly harmonic maps from the unit ball $B= B(m) \subset \mathbb{R}^m $ $(m\geq2)$ into certain pseudo-Riemannian manifolds: standard stationary Lorentzian manifolds, pseudospheres $\mathbb{S}^n_ν\subset \mathbb{R}^{n+1}_ν$ $(1\leqν\leq n)$ and pseudohyperbolic spaces $\mathbb{H}^n_ν\subset \mathbb{R}^{n+1}_{ν+1}$ $(0\leqν\leq n-1)$. Consequently, such maps are shown to be Hölder continuous (and as smooth as the regulari…

通过分数阶差商研究极弱s-调和函数的局部正则性

Local Regularity of very weak $s$-harmonic functions via fractional difference quotients

本文提出通过改进局部可和性、适配分数阶差商方法消除积分核奇异性并结合标准椭圆正则性方法，新证单位球中极弱s-调和函数的实解析性，相关差商技术为首次提出。

Regularity of n/2-harmonic maps into spheres

We prove Hoelder continuity for n/2-harmonic maps from subsets of Rn into a sphere. This extends a recent one-dimensional result by F. Da Lio and T. Riviere to arbitrary dimensions. The proof relies on compensation effects which we quantify adapting an approach for Wente's inequality by L. Tartar, instead of Besov-space arguments which were used in the one-dimensional case. Moreover, fractional analogues of Hodge decomposition and higher order Poincare inequalities as well as several localization effects for nonlocal operators similar to the fractional laplacian are developed and applied.

A conditional regularity result for p-harmonic flows

We prove an $\varepsilon$-regularity result for a wide class of parabolic systems $$ u_t-\text{div}\big(|\nabla u|^{p-2}\nabla u) = B(u, \nabla u) $$ with the right hand side $B$ growing like $|\nabla u|^p$. It is assumed that the solution $u(t,\cdot)$ is uniformly small in the space of functions of bounded mean oscillation. The crucial tool is provided by a sharp nonlinear version of the Gagliardo-Nirenberg inequality which has been used earlier in an elliptic context by T. Rivière and the last named author.

Regularity at the free boundary for Dirac-harmonic maps from surfaces

We establish the regularity theory for certain critical elliptic systems with an anti-symmetric structure under inhomogeneous Neumann and Dirichlet boundary constraints. As applications, we prove full regularity and smooth estimates at the free boundary for weakly Dirac-harmonic maps from spin Riemann surfaces. Our methods also lead to the full interior $ε$-regularity and smooth estimates for weakly Dirac-harmonic maps in all dimensions.

1/2-调和映射的定量分层与全局正则性

Quantitative stratification and global regularity for 1/2-harmonic mappings

本文将Naber-Valtorta的全局正则性理论扩展到映射中的1/2-调和映射，通过改进的缺陷测度理论和Caffarelli-Silverstre的调和扩展方法，实现了奇异点的定量分层，并建立了奇异层的可测性。

Regularity for Dirac-harmonic maps into certain pseudo-Riemannian manifolds

We show the smoothness of weakly Dirac-harmonic maps from a closed spin Riemann surface into stationary Lorentzian manifolds, and obtain a regularity theorem for a class of critical elliptic systems without anti-symmetry structures.

Partial regularity for harmonic maps, and related problems

Via Gauge theory, we give a new proof of partial regularity for harmonic maps in dimension m>2 into arbitrary targets. This proof avoids the use of adapted frames and permits to consider targets of "minimal" C^2 regularity. The proof we present moreover extends to a large class of elliptic systems of quadratic growth.

$C^1$ regularity of orthotropic $p-$harmonic functions in the plane

We prove that local weak solutions of the orthotropic $p-$harmonic equation in $\mathbb{R}^2$ are $C^1$ functions.

Regularity for minimizers of functionals with nonstandard growth by $A$-harmonic approximation

We prove partial regularity for minimizers of quasiconvex functionals of the type $\int_Ωf(x,Du) dx$ with $p(x)$ growth with respect to the second variable. The proof is direct and uses a method of $A$-harmonic approximation.

Regularity results for the time-harmonic Maxwell equations with impedance boundary condition

This paper considers the time-harmonic Maxwell equations with impedance boundary condition.We present $H^2$-norm bound and other high-order norm bounds for strong solutions. The $H^2$-estimate have been derived in [M. Dauge, M. Costabel and S. Nicaise, Tech. Rep. 10-09, IRMAR (2010)] for the case with homogeneous boundary condition. Unfortunately, their method can not be applied to the inhomogeneous case. The main novelty of this paper is that we follow the spirit of the $H^1$-estimate in [R. Hiptmair, A. Moiola and I. Perugia, Math. Models Methods Appl. Sci., 21(2011), pp. 2263-2287] and modi…

Regularity of Minimizers for a General Class of Constrained Energies in Two-Dimensional Domains with Applications to Liquid Crystals

We investigate minimizers defined on a bounded domain $Ω$ in $\mathbb{R}^2$ for singular constrained energy functionals that include Ball and Majumdar's modification of the Landau-de Gennes Q-tensor model for nematic liquid crystals. We prove regularity of minimizers with finite energy and show that their range on compact subdomains of $Ω$ does not intersect the boundary of the constraining set.

The Kellogg property and boundary regularity for p-harmonic functions with respect to the Mazurkiewicz boundary and other compactifications

In this paper boundary regularity for p-harmonic functions is studied with respect to the Mazurkiewicz boundary and other compactifications. In particular, the Kellogg property (which says that the set of irregular boundary points has capacity zero) is obtained for a large class of compactifications, but also two examples when it fails are given. This study is done for complete metric spaces equipped with doubling measures supporting a p-Poincaré inequality, but the results are new also in unweighted Euclidean spaces.

Partial regularity of the heat flow of half-harmonic maps and applications to harmonic maps with free boundary

We introduce a heat flow associated to half-harmonic maps, which have been introduced by Da Lio and Rivière. Those maps exhibit integrability by compensation in one space dimension and are related to harmonic maps with free boundary. We consider a new flow associated to these harmonic maps with free boundary which is actually motivated by a rather unusual heat flow for half-harmonic maps. We construct then weak solutions and prove their partial regularity in space and time via a Ginzburg-Landau approximation. The present paper complements the study initiated by Struwe and Chen-Lin.

在Lyapunov域之间谐波拟共形映射的Lipschitz正则性

Lipschitz regularity of harmonic quasiconformal maps between Lyapunov domains in $\mathbb{R}^n$

研究在Lyapunov域之间谐波拟共形映射的Lipschitz正则性，通过边界迭代方案和调和测度界证明其全局Lipschitz性质。

Regularity of Dirac-harmonic maps

For any $n$-dimensional compact spin Riemannian manifold $M$ with a given spin structure and a spinor bundle $ΣM$, and any compact Riemannian manifold $N$, we show an $ε$-regularity theorem for weakly Dirac-harmonic maps . As a consequence, any weakly Dirac-harmonic map is proven to be smooth when n = 2. A weak convergence theorem for approximate Dirac-harmonic maps is established when $n = 2$. For $n \ge 3$, we introduce the notation of stationary Dirac-harmonic maps and obtain a Liouville theorem for stationary Dirac-harmonic maps in $R^n$. If, additions, $ψ\in W^{1,p}$ for some $p>2n/3$, th…

Regularity of solutions to time-harmonic Maxwell's system with various lower than Lipschitz coefficients

In this paper, we study the regularity of the solutions of Maxwell's equations in a bounded domain. We consider several different types of low regularity assumptions to the coefficients which are all less than Lipschitz. We first develop a new approach by giving $\mathcal{H}^1$ estimate when the coefficients are $\mathcal{L}^{\infty}$ bounded; and then we derive $\mathcal{W}^{1,p}$ estimates for every $p > 2$ when one of the leading coefficients is simply continuous; Finally, we extend the result to $\mathcal{C}^{1,α}$ almost everywhere for the solution of the homogeneous Maxwell's equations w…

Regularity of harmonic discs in spaces with quadratic isoperimetric inequality

We study harmonic and quasi-harmonic discs in metric spaces admitting a uniformly local quadratic isoperimetric inequality for curves. The class of such metric spaces includes compact Lipschitz manifolds, metric spaces with upper or lower curvature bounds in the sense of Alexandrov, some sub-Riemannian manifolds, and many more. In this setting, we prove local Hoelder continuity and continuity up to the boundary of harmonic and quasi-harmonic discs.

关于具有任意坐标个数的调和特征映射的正则性估计

Regularity estimates on harmonic eigenmaps with arbitrary number of coordinates

本文重新审视曲面上调和映射的正则性估计对目标流形维数的独立性，研究映射到目标椭球体的 Laplace 调和特征映射，并收集工具处理几乎临界度量的收敛，为特征值无限组合的临界点的一般正则性理论提供初步步骤。

谐波近复结构的定量分层与最优正则性

Quantitative stratification and optimal regularity for harmonic almost complex structures

本文通过定量分层方法改进了谐波近复结构的正则性理论，建立了最优正则性结果。

Almost Everywhere Regularity for the Free Boundary of the Normalized p-harmonic Obstacle problem $p>2$

Let $u$ be a solution to the normalized p-harmonic obstacle problem with $p>2$. That is, $u\in W^{1,p}(B_1(0))$, $2<p<\infty$, $u\ge 0$ and $$ \d\left( |\nabla u|^{p-2}\nabla u\right)=χ_{\{u>0\}}\textrm{ in }B_1(0) $$ where $u(x)\ge 0$ and $χ_A$ is the characteristic function of the set $A$. Our main result is that for almost every free boundary point, with respect to the $(n-1)-$Hausdorff measure, there is a neighborhood where the free boundary is a $C^{1,β}-$graph. That is, for $\H^{n-1}-$a.e. point $x^0\in \partial \{u>0\}\cap B_1(0)$ there is an $r>0$ such that $B_r(x^0)\cap \partial \{u>0…

Regularity and decay of solutions of nonlinear harmonic oscillators

We prove sharp analytic regularity and decay at infinity of solutions of variable coefficients nonlinear harmonic oscillators. Namely, we show holomorphic extension to a sector in the complex domain, with a corresponding Gaussian decay, according to the basic properties of the Hermite functions in R^d. Our results apply, in particular, to nonlinear eigenvalue problems for the harmonic oscillator associated to a real-analytic scattering, or asymptotically conic, metric in R^d, as well as to certain perturbations of the classical harmonic oscillator.

Regularity for a geometrically nonlinear flat Cosserat micropolar membrane shell with curvature

We consider the rigorously derived thin shell membrane $Γ$-limit of a three-dimensional isotropic geometrically nonlinear Cosserat micropolar model and deduce full interior regularity of both the midsurface deformation $m:ω\subset{\mathbb R}^2\to{\mathbb R}^3$ and the orthogonal microrotation tensor field $R:ω\subset{\mathbb R}^2\to SO(3)$. The only further structural assumption is that the curvature energy depends solely on the uni-constant isotropic Dirichlet type energy term $|DR|^2$. We use Rivière's regularity techniques of harmonic map type systems for our system which couples harmonic m…