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arXiv math/0201232math.APmath.DG
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黎曼流形上的一个尖锐Sobolev不等式

A sharp Sobolev inequality on Riemannian manifolds

YanYan Li, Tonia Ricciardi

摘要:

设(M,g)是n ≥ 6维无边界的光滑紧致黎曼流形.证明了{align*} u L^{2^*}(M,g)}^2 \le K^2 \int_M| \nabla_g使用|对于所有的\in H^1(M),有^2+c(n)R_gu^2\}dv_g +A\|u\|_{L^{2n/(n+2)}(M,g)}^2,{align*},其中2^*=2n/(n-2),c(n)=(n-2)/[4(n-1)],R_g是标量曲率,$K^{-1}=\inf\|\nabla u\|_{L^2(\R^n)}\|u\|_{L^{2n/(n-2)}(\R^n)}^{-1}$,A>0是只依赖于(M,g)的常数.这个不等式是{ \em sharp},即在任何(M,g)上,$K$不能被任何更小的数代替,R_g不能被任何在某点小于R_g的连续函数代替.如果(M,g)不是局部共形平坦的,则指数2n/(n+2)不能用任何更小的数代替.如果(M,g)是局部共形平坦的,则一个更强的不等式,将2n/(n+2)替换为1,在所有维数n>=3中成立。

英文摘要:

Let (M,g) be a smooth compact Riemannian manifold without boundary of dimension n>=6. We prove that {align*} \|u\|_{L^{2^*}(M,g)}^2 \le K^2\int_M\{|\nabla_g u|^2+c(n)R_gu^2\}dv_g +A\|u\|_{L^{2n/(n+2)}(M,g)}^2, {align*} for all u\in H^1(M), where 2^*=2n/(n-2), c(n)=(n-2)/[4(n-1)], R_g is the scalar curvature, $K^{-1}=\inf\|\nabla u\|_{L^2(\R^n)}\|u\|_{L^{2n/(n-2)}(\R^n)}^{-1}$ and A>0 is a constant depending on (M,g) only. The inequality is {\em sharp} in the sense that on any (M,g), $K$ can not be replaced by any smaller number and R_g can not be replaced by any continuous function which is smaller than R_g at some point. If (M,g) is not locally conformally flat, the exponent 2n/(n+2) can not be replaced by any smaller number. If (M,g) is locally conformally flat, a stronger inequality, with 2n/(n+2) replaced by 1, holds in all dimensions n>=3.

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