Sharp Sobolev inequalities on the complex sphere

Abstract

This paper is devoted to establish a class of sharp Sobolev inequalities on the unit complex sphere as follows: 1) Case $0<d<Q=2n+2$: for any $f\in C^{\infty }$ and $2\le q\le \frac{2Q}{Q-d}$, \begin{equation*} \|f\|_q^2\leq \frac{8(q-2)}{d(Q-d)} \frac{Γ^2((Q-d)/4+1)} {Γ^2((Q+d)/4)}\left( \int_{\mathbb{S}^{2n+1}} f\mathcal{A}_df dξ -\frac{Γ^2((Q+d)/4)} {Γ^2((Q-d)/4)} \int_{\mathbb{S}^{2n+1}} |f|^2 dξ\right) +\int_{\mathbb{S}^{2n+1}} |f|^2 dξ; \end{equation*} 2) Case $d=Q$: for any $f\in C^{\infty }\cap \mathbb{R}\mathcal{P}$ and $2\le q<+\infty$, \begin{equation*} \|f\|_q^2\leq \frac{q-2}{(n+1)!} \int_{\mathbb{S}^{2n+1}} f \mathcal{A}'_Q f dξ+\int_{\mathbb{S}^{2n+1}} |f|^2 dξ, \end{equation*} where ${\mathcal{A}}_d(0<d<Q)$ are the intertwining operator, ${\mathcal{A}}_Q^{\prime }$ is the conditional intertwinor introduced in \cite{BFM2013}, and $d\xi$ is the normalized surface measure of ${\mathbb{S}}^{2n+1}$.