Journal of Pure and Applied Algebra ( IF 0.8 ) Pub Date : 2020-09-11 , DOI: 10.1016/j.jpaa.2020.106569 A.S. Sivatski
Let F be a field, . Assume that are such that are linearly independent over . As usual stands for the Witt ring of F. For an element denote by dim φ the dimension of the corresponding anisotropic quadratic form. Define as the maximum of dim φ, where φ runs over the set of elements in , which become zero in . This is a version of the classical notion of the u-invariant of the field F. It turns out that for any , where the sequence is defined recurrently as , and .
We compute in certain cases, and show that , where . However, in general there is no lower bound for via , even though we prove that .
Let be the maximum of , where a runs over all elements of . We show that if b is a sum of two squares. In particular, the last inequality holds if .
中文翻译:
字段的U不变量的某些版本
设F为一个场,。假使,假设 如此 线性独立于 。照常代表F的Witt环。对于元素在昏暗的表示 φ相应的各向异性二次型的尺寸。定义作为最大暗淡 φ,其中φ运行在集合中的元素的,在其中变为零 。这是u不变量的经典概念的一个版本F的场。事实证明 对于任何 ,其中顺序 经常被定义为 和 。
我们计算 在某些情况下,并表明 ,在哪里 。但是,通常没有下限 通过 ,即使我们证明 。
让 是最大的 ,其中a遍历了所有元素。我们证明如果b是两个平方的和。特别是,如果。