Best constants in a borderline case of second-order Moser type inequalities

Cassani, Daniele ; Ruf, Bernhard  ; Tarsi, Cristina 

Annales de l'I.H.P. Analyse non linéaire, Tome 27 (2010) no. 1, pp. 73-93

Résumé

We study optimal embeddings for the space of functions whose Laplacian Δu belongs to $L^1\left(\Omega \right)$, where $\Omega \subset {ℝ}^N$ is a bounded domain. This function space turns out to be strictly larger than the Sobolev space $W^{2,1}\left(\Omega \right)$ in which the whole set of second-order derivatives is considered. In particular, in the limiting Sobolev case, when $N=2$, we establish a sharp embedding inequality into the Zygmund space $L_{\mathrm{𝑒𝑥𝑝}}\left(\Omega \right)$. On one hand, this result enables us to improve the Brezis–Merle (Brezis and Merle (1991) [13]) regularity estimate for the Dirichlet problem $\Delta u=f\left(x\right)\in L^1\left(\Omega \right)$, $u=0$ on ∂Ω; on the other hand, it represents a borderline case of D.R. Adams' (1988) [1] generalization of Trudinger–Moser type inequalities to the case of higher-order derivatives. Extensions to dimension $N⩾3$ are also given. Besides, we show how the best constants in the embedding inequalities change under different boundary conditions.

Détail

DOI : 10.1016/j.anihpc.2009.07.006

Classification : 46E35, 35B65
Keywords: Sobolev embeddings, Pohožaev, Strichartz and Trudinger–Moser inequalities, Best constants, Elliptic equations, Regularity estimates in $ {L}^{1}$, Brezis–Merle type results