arXiv subjects

Xiangjin Xu

Publications and source records attributed to Xiangjin Xu.

5 recordsLinked to original sources

arXiv2025

$L^p$-Logvinenko-Sereda sets and $L^p$-Carleson measures on compact manifolds

Marzo and Ortega-Cerdà gave geometric characterizations for $L^p$-Logvinenko-Sereda sets on the standard sphere for all $1\le p<\infty$. Later, Ortega-Cerdà and Pridhnani further investigated $L^2$-Logvinenko-Sereda sets and $L^2$-Carleson measures on compact manifolds without boundary. In this paper, we characterize $L^p$-Logvinenko-Sereda sets and $L^p$-Carleson measures on compact manifolds with or without boundary for all $1 \frac{2m}{m-1}$. For the range $p < \frac{2m}{m-1}$, we conjecture that $L^p$-Logvinenko-Sereda sets for eigenfunctions on the standard sphere $S^m$ are characterized by the tubular geometric control condition and we provide some evidence. These results provide new progress on an open problem raised by Ortega-Cerdà and Pridhnani.

math.AP↗

arXiv2019

Heat kernel Gaussian bounds on manifolds I: manifolds with non-negative Ricci curvature

This is first of series papers on new two-side Gaussian bounds for the heat kernel $H(x,y,t)$ on a complete manifold $(M,g)$. In this paper, on a complete manifold $M$ with $Ric(M)\geq 0$, we obtain new two-side Gaussian bounds for the heat kernel $H(x,y,t)$, which improve the well-known Li-Yau's two-side bounds. As applications of our new two-side Gaussian bounds, We obtain a sharp gradient estimate and a Laplacian estimate for the heat kernel on a complete manifold with $Ric(M)\geq 0$, and we also give a simpler proof for the result concerning the asymptotic behavior in the time variable for the heat kernel as was proved in \cite{LiP-1} on a complete manifold $M$ with $Ric(M)\geq 0$ and maximal volume growth.

math.DG↗

arXiv2011

Upper and lower bounds for normal derivatives of spectral clusters of Dirichlet Laplacian

In this paper, we prove the upper and lower bounds for normal derivatives of spectral clusters $u=χ_λ^s f$ of Dirichlet Laplacian $Δ_M$, $$c_s λ\|u\|_{L^2(M)} \leq \| \partial_νu \|_{L^2(\partial M)} \leq C_s λ\|u\|_{L^2(M)} $$ where the upper bound is true for any Riemannian manifold, and the lower bound is true for some small $0<s<s_M$, where $s_M$ depends on the manifold only, provided that $M$ has no trapped geodesics (see Theorem \ref{Thm3} for a precise statement), which generalizes the early results for single eigenfunctions by Hassell and Tao.

math.AP↗

arXiv2011

Gradient estimates for $u_t=ΔF(u)$ on manifolds and some Liouville-type theorems

In this paper, we first prove a localized Hamilton-type gradient estimate for the positive solutions of Porous Media type equations: $$u_t=ΔF(u),$$ with $F'(u) > 0$, on a complete Riemannian manifold with Ricci curvature bounded from below. In the second part, we study Fast Diffusion Equation (FDE) and Porous Media Equation (PME): $$u_t=Δ(u^p),\qquad p>0,$$ and obtain localized Hamilton-type gradient estimates for FDE and PME in a larger range of $p$ than that for Aronson-Bénilan estimate, Harnack inequalities and Cauchy problems in the literature. Applying the localized gradient estimates for FDE and PME, we prove some Liouville-type theorems for positive global solutions of FDE and PME on noncompact complete manifolds with nonnegative Ricci curvature, generalizing Yaus celebrated Liouville theorem for positive harmonic functions.

math.AP↗

arXiv2009

Differential Harnack inequalities on Riemannian manifolds I : linear heat equation

In the first part of this paper, we get new Li-Yau type gradient estimates for positive solutions of heat equation on Riemmannian manifolds with $Ricci(M)\ge -k$, $k\in \mathbb R$. As applications, several parabolic Harnack inequalities are obtained and they lead to new estimates on heat kernels of manifolds with Ricci curvature bounded from below. In the second part, we establish a Perelman type Li-Yau-Hamilton differential Harnack inequality for heat kernels on manifolds with $Ricci(M)\ge -k$, which generalizes a result of L. Ni \cite{NL1,NL4}. As applications, we obtain new Harnack inequalities and heat kernel estimates on general manifolds. We also obtain various entropy monotonicity formulas for all compact Riemannian manifolds.

math.DG↗