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arXiv math/0008088math.SPmath-phmath.MP
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S^n中半球区域的前两个Dirichlet特征值之比的一个精确界

A Sharp Bound for the Ratio of the First Two Dirichlet Eigenvalues of a Domain in a Hemisphere of S^n

Mark S. Ashbaugh, Rafael D. Benguria

摘要:

对于域$Ω$包含在一个半球的$n$维球体$\SS^n$,我们证明了最佳结果$λ_2/λ_1(Ω) \le λ_2/λ_1(Ω^{\star})$的第一个两个Dirichlet特征值的比例,其中$Ω^{\star}$,对称重排的$Ω$在$\SS^n$,是一个测地球在$\SS^n$具有相同的$n$体积的$Ω$。我们还表明,$λ_2/λ_1$测地球的测地半径$θ_1$小于或等于$π/2$是$θ_1$之间运行的值$(j_{n/2,1}/j_{n/2-1,1})^2$ $θ_1=0$(这是欧几里德值)和$2(n+1)/n$为$θ_1=π/2$的$θ_1$的增函数。这里,$j_{ν,k}$表示贝塞尔函数$J_ν(t)$的$k^{th}$正零点。这一结果推广了Payne-Pólya-Weinberger猜想,该猜想适用于欧氏空间中的有界域,并且我们已经证明了。我们的方法利用对称重排的功能和各种技术性能的特殊功能。我们还证明了在包含在一个半球的$\SS^n$,并有一个固定的$λ_1$值的所有域的$λ_2$的最大值是适当半径的测地线球。这是一个比$λ_2/λ_1$更强的等周结果,但稍难获得。在我们的工作过程中,证明了在$\SS^n$中测地球的$λ_1$和$λ_2$的各种其他结果。

英文摘要:

For a domain $Ω$ contained in a hemisphere of the $n$-dimensional sphere $\SS^n$ we prove the optimal result $λ_2/λ_1(Ω) \le λ_2/λ_1(Ω^{\star})$ for the ratio of its first two Dirichlet eigenvalues where $Ω^{\star}$, the symmetric rearrangement of $Ω$ in $\SS^n$, is a geodesic ball in $\SS^n$ having the same $n$-volume as $Ω$. We also show that $λ_2/λ_1$ for geodesic balls of geodesic radius $θ_1$ less than or equal to $π/2$ is an increasing function of $θ_1$ which runs between the value $(j_{n/2,1}/j_{n/2-1,1})^2$ for $θ_1=0$ (this is the Euclidean value) and $2(n+1)/n$ for $θ_1=π/2$. Here $j_{ν,k}$ denotes the $k^{th}$ positive zero of the Bessel function $J_ν(t)$. This result generalizes the Payne-Pólya-Weinberger conjecture, which applies to bounded domains in Euclidean space and which we had proved earlier. Our method makes use of symmetric rearrangement of functions and various technical properties of special functions. We also prove that among all domains contained in a hemisphere of $\SS^n$ and having a fixed value of $λ_1$ the one with the maximal value of $λ_2$ is the geodesic ball of the appropriate radius. This is a stronger, but slightly less accessible, isoperimetric result than that for $λ_2/λ_1$. Various other results for $λ_1$ and $λ_2$ of geodesic balls in $\SS^n$ are proved in the course of our work.

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