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arXiv 1508.04784math-phmath.MP
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分形的复维数与分形 zeta 函数的亚纯延拓

Complex dimensions of fractals and meromorphic extensions of fractal zeta functions

Michel L. Lapidus, Goran Radunović, Darko Žubrinić

AI总结:

本文研究分形距离、管及分形弦几何 zeta 函数的亚纯延拓,利用管函数渐近展开界定延拓域并联系留数与 Minkowski 容度,还构造了具高阶主复维数和无穷本质奇点的分形弦。

摘要:

我们研究距离 zeta 函数和管 zeta 函数,以及分形弦的几何 zeta 函数的亚纯延拓。距离 zeta 函数 $ζ_A(s):=\int_{A_δ} d(x,A)^{s-N}\mathrm{d}x$(其中固定 $δ>0$,$d(x,A)$ 表示从 $x$ 到 $A$ 的欧氏距离)将与有界分形弦相关的 zeta 函数定义推广到 $\mathbb{R}^N$ 的任意有界子集 $A$。Lebesgue 收敛横坐标 $D(ζ_A)$ 与 $D:=\overline\dim_BA$(即 $A$ 的上盒维数)一致。$A$ 的复维数是 $A$ 的分形 zeta 函数向“临界线”$\{\Re(s)=D\}$ 的某个适当连通邻域作亚纯延拓后的极点。在假定掌握管函数 $|A_t|$(其中 $A_t$ 是 $A$ 的欧氏 $t$-邻域)当 $t\to0^+$ 时渐近展开第二项的适当信息的条件下,我们建立了若干亚纯延拓结果。我们特别关注一类 Minkowski 可测集,满足当 $t\to0^+$ 时 $|A_t|=t^{N-D}(\mathcal M+O(t^γ))$,其中 $γ>0$;以及一类 Minkowski 不可测集,满足当 $t\to0^+$ 时 $|A_t|=t^{N-D}(G(\log t^{-1})+O(t^γ))$,其中 $G$ 是非常值周期函数且 $γ>0$。在两种情形下,我们都证明 $ζ_A$ 可以亚纯延拓(至少)到开右半平面 $\{\Re(s)>D-γ\}$。此外,我们证明,在相差一个乘法常数的意义下,$ζ_A$ 在 $s=D$ 处的留数分别等于 $\mathcal M$($A$ 的 Minkowski 容度)和 $G$ 的平均值($A$ 的平均 Minkowski 容度)。而且,我们构造了一类分形弦,其具有任意指定阶数的主复维数,并在临界线 $\{\Re(s)=D\}$ 上具有无穷多个本质奇点。

英文摘要:

We study meromorphic extensions of distance and tube zeta functions, as well as of geometric zeta functions of fractal strings. The distance zeta function $ζ_A(s):=\int_{A_δ} d(x,A)^{s-N}\mathrm{d}x$, where $δ>0$ is fixed and $d(x,A)$ denotes the Euclidean distance from $x$ to $A$ extends the definition of the zeta function associated with bounded fractal strings to arbitrary bounded subsets $A$ of $\mathbb{R}^N$. The abscissa of Lebesgue convergence $D(ζ_A)$ coincides with $D:=\overline\dim_BA$, the upper box dimension of $A$. The complex dimensions of $A$ are the poles of the meromorphic continuation of the fractal zeta function of $A$ to a suitable connected neighborhood of the "critical line" $\{\Re(s)=D\}$. We establish several meromorphic extension results, assuming some suitable information about the second term of the asymptotic expansion of the tube function $|A_t|$ as $t\to0^+$, where $A_t$ is the Euclidean $t$-neighborhood of $A$. We pay particular attention to a class of Minkowski measurable sets, such that $|A_t|=t^{N-D}(\mathcal M+O(t^γ))$ as $t\to0^+$, with $γ>0$, and to a class of Minkowski nonmeasurable sets, such that $|A_t|=t^{N-D}(G(\log t^{-1})+O(t^γ))$ as $t\to0^+$, where $G$ is a nonconstant periodic function and $γ>0$. In both cases, we show that $ζ_A$ can be meromorphically extended (at least) to the open right half-plane $\{\Re(s)>D-γ\}$. Furthermore, up to a multiplicative constant, the residue of $ζ_A$ evaluated at $s=D$ is shown to be equal to $\mathcal M$ (the Minkowski content of $A$) and to the mean value of $G$ (the average Minkowski content of $A$), respectively. Moreover, we construct a class of fractal strings with principal complex dimensions of any prescribed order, as well as with an infinite number of essential singularities on the critical line $\{\Re(s)=D\}$.

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