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arXiv 1303.1005math.NT
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多元洛朗级数域的Pythagoras数和$u$ -不变量

The Pythagoras number and the $u$-invariant of Laurent series fields in several variables

Yong Hu

摘要:

我们证明了三变量洛朗级数域$\mathbb{R}((x,y,z))$中的每一个平方和都是4个平方的和,正如Choi,Dai,Lam和Reznick在20世纪80年代的一篇论文中所证明的那样。我们通过证明$\mathbb{R}((x,y))$的有限扩张中的每一个平方和都是$3$平方和来得到这个结果。它已经表明,在崔,戴,林和Reznick的文件,每一个平方和$\mathbb{R}((x,y))$本身是一个总和的两个平方。我们给出了这个结果的一个推广,其中$\mathbb{R}$被替换为任意实域。我们的方法产生类似的结果,$u$不变的字段的相同类型。

英文摘要:

We show that every sum of squares in the three-variable Laurent series field $\mathbb{R}((x,y,z))$ is a sum of 4 squares, as was conjectured in a paper of Choi, Dai, Lam and Reznick in the 1980's. We obtain this result by proving that every sum of squares in a finite extension of $\mathbb{R}((x,y))$ is a sum of $3$ squares. It was already shown in Choi, Dai, Lam and Reznick's paper that every sum of squares in $\mathbb{R}((x,y))$ itself is a sum of two squares. We give a generalization of this result where $\mathbb{R}$ is replaced by an arbitrary real field. Our methods yield similar results about the $u$-invariant of fields of the same type.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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