English

A real-valued measure on non-Archimedean field extensions of $\mathbb{R}$

Functional Analysis 2020-09-30 v1

Abstract

We introduce a real-valued measure mL{m_L} on non-Archimedean ordered fields (F,<)(\mathbb{F},<) that extend the field of real numbers (R,<)(\mathbb{R},<). The definition of mL{m_L} is inspired by the Loeb measures of hyperreal fields in the framework of Robinson's analysis with infinitesimals. The real-valued measure mL{m_L} turns out to be general enough to obtain a canonical measurable representative in F\mathbb{F} for every Lebesgue measurable subset of R\mathbb{R}, moreover, the measure of the two sets is equal. In addition, mLm_L it is more expressive than a class of non-Archimedean uniform measures. We focus on the properties of the real-valued measure in the case where F=R\mathbb{F}=\mathcal{R}, the Levi-Civita field. In particular, we compare mL{m_L} with the uniform non-Archimedean measure over R\mathcal{R} developed by Shamseddine and Berz, and we prove that the first is infinitesimally close to the second, whenever the latter is defined. We also define a real-valued integral for functions on the Levi-Civita field, and we prove that every real continuous function has an integrable representative in R\mathcal{R}. Recall that this result is false for the current non-Archimedean integration over R\mathcal{R}. The paper concludes with a discussion on the representation of the Dirac distribution by pointwise functions on non-Archimedean domains.

Keywords

Cite

@article{arxiv.2009.14086,
  title  = {A real-valued measure on non-Archimedean field extensions of $\mathbb{R}$},
  author = {Emanuele Bottazzi},
  journal= {arXiv preprint arXiv:2009.14086},
  year   = {2020}
}