Searcharxiv⌕ Search

arXiv subjects

Sasikarn Yeepo

Publications and source records attributed to Sasikarn Yeepo.

5 recordsLinked to original sources
arXiv2024

Calderon-Zygmund theory for strongly coupled linear system of nonlocal equations with Holder-regular coefficient

We extend the Calderón-Zygmund theory for nonlocal equations to strongly coupled system of linear nonlocal equations $\mathcal{L}^{s}_{A} u = f$, where the operator $\mathcal{L}^{s}_{A}$ is formally given by \[ \mathcal{L}^s_{A}u = \int_{\mathbb{R}^n}\frac{A(x, y)}{\vert x-y\vert ^{n+2s}} \frac{(x-y)\otimes (x-y)}{\vert x-y\vert ^2}(u(x)-u(y))dy. \] For $0 < s < 1$ and $A:\mathbb{R}^{n} \times \mathbb{R}^{n} \to \mathbb{R}$ taken to be symmetric and serving as a variable coefficient for the operator, the system under consideration is the fractional version of the classical Navier-Lamé linearized elasticity system. The study of the coupled system of nonlocal equations is motivated by its appearance in nonlocal mechanics, primarily in peridynamics. Our regularity result states that if $A(\cdot, y)$ is uniformly Holder continuous and $\inf_{x\in \mathbb{R}^n}A(x, x) > 0$, then for $f\in L^{p}_{loc},$ for $p\geq 2$, the solution vector $u\in H^{2s-δ,p}_{loc}$ for some $δ\in (0, s)$.

math.AP↗
arXiv2021

Calderon-Zygmund theory for non-convolution type nonlocal equations with continuous coefficient

Given $2\leq p<\infty$, $s\in (0, 1)$ and $t\in (1, 2s)$, we establish interior $W^{t,p}$ Calderon-Zygmund estimates for solutions of nonlocal equations of the form \[ \int_Ω \int_Ω K\left (x,|x-y|,\frac{x-y}{|x-y|}\right ) \frac{(u(x)-u(y))(φ(x)-φ(y))}{|x-y|^{n+2s}} dx dy = g[φ], \quad \forall ϕ\in C_c^{\infty}(Ω) \] where $Ω\subset \mathbb{R}^{n}$ is an open set. Here we assume $K$ is bounded, nonnegative and continuous in the first entry -- and ellipticity is ensured by assuming that $K$ is strictly positive in a cone. The setup is chosen so that it is applicable for nonlocal equations on manifolds, but the structure of the equation is general enough that it also applies to the certain fractional $p$-Laplace equations around points where $u \in C^1$ and $|\nabla u| \neq 0$.

math.AP↗
arXiv2020

On the Calderon-Zygmund property of Riesz-transform type operators arising in nonlocal equations

We show that the operator \[ T_{K,s_1,s_2}f(z) := \int_{\mathbb{R}^n} A_{K,s_1,s_2}(z_1,z_2) f(z_2)\, dz_2 \] is a Calderon-Zygmund operator. Here for $K \in L^\infty(\mathbb{R}^n \times \mathbb{R}^n)$, and $s,s_1,s_2 \in (0,1)$ with $s_1+s_2 = 2s$ we have \[ A_{K,s_1,s_2}(z_1,z_2) = \int_{\mathbb{R}^n} \int_{\mathbb{R}^n} \frac{K(x,y) \left (|x-z_1|^{s_1-n} -|y-z_1|^{s_1-n} \right )\, \left (|x-z_2|^{s_2-n} -|y-z_2|^{s_2-n}\right )}{|x-y|^{n+2s}}\, dx\, dy. \] This operator is motivated by the recent work by Mengesha-Schikorra-Yeepo where it appeared as analogue of the Riesz transforms for the equation \[ \int_{\mathbb{R}^n} \int_{\mathbb{R}^n} \frac{K(x,y) (u(x)-u(y))\, (φ(x)-φ(y))}{|x-y|^{n+2s}}\, dx\, dy = f[φ]. \]

math.AP↗
arXiv2020

Calderon-Zygmund type estimates for nonlocal PDE with Hölder continuous kernel

We study interior $L^p$-regularity theory, also known as Calderon-Zygmund theory, of the equation \[ \int_{\mathbb{R}^n} \int_{\mathbb{R}^n} \frac{K(x,y)\ (u(x)-u(y))\, (φ(x)-φ(y))}{|x-y|^{n+2s}}\, dx\, dy = \langle f, φ\rangle \quad φ\in C_c^\infty(\mathbb{R}^n). \] For $s \in (0,1)$, $t \in [s,2s]$, $p \in [2,\infty)$, $K$ an elliptic, symmetric, Hölder continuous kernel, if $f \in \left (H^{t,p'}_{00}(Ω)\right )^\ast$, then the solution $u$ belongs to $H^{2s-t,p}_{loc}(Ω)$ as long as $2s-t < 1$. The increase in differentiability is independent of the Hölder coefficient of $K$. For example, our result shows that if $f\in L^{p}_{loc}$ then $u\in H^{2s-δ,p}_{loc}$ for any $δ\in (0, s]$ as long as $2s-δ< 1$. This is different than the classical analogue of divergence-form equations ${\rm div}(\bar{K} \nabla u) = f$ (i.e. $s=1$) where a $C^γ$-Hölder continuous coefficient $\bar{K}$ only allows for estimates of order $H^{1+γ}$. In fact, it is another appearance of the differential stability effect observed in many forms by many authors for this kind of nonlocal equations -- only that in our case we do not get a "small" differentiability improvement, but all the way up to $\min\{2s-t,1\}$. The proof argues by comparison with the (much simpler) equation \[ \int_{\mathbb{R}^n} K(z,z) (-Δ)^{\frac{t}{2}} u(z) \, (-Δ)^{\frac{2s-t}{2}} φ(z)\, dz = \langle g,φ\rangle \quad φ\in C_c^\infty(\mathbb{R}^n). \] and showing that as long as $K$ is Hölder continuous and $s,t, 2s-t \in (0,1)$ then the "commutator" \[ \int_{\mathbb{R}^n} K(z,z) (-Δ)^{\frac{t}{2}} u(z) \, (-Δ)^{\frac{2s-t}{2}} φ(z)\, dz - c\int_{\mathbb{R}^n} \int_{\mathbb{R}^n} \frac{K(x,y)\ (u(x)-u(y))\, (φ(x)-φ(y))}{|x-y|^{n+2s}}\, dx\, dy \] behaves like a lower order operator.

math.AP↗