Real dimensional spaces in noncommutative geometry

Abstract

In this paper we will extend the product of spectral triples to a product of semifinite spectral triples. We will prove that finite summability and regularity are preserved under taking products. Connes and Marcolli constructed for each $z\in(0,\infty)$ a type ${\rm II}_\infty$-semifinite spectral triple which can be considered as a geometric space of dimension $z$. A small adaption of their construction yields a type ${\rm I}$-semifinite spectral triple. We will investigate the properties of these semifinite spectral triples. At the same time we will also avoid the need for an infra-red cutoff to compute the dimension spectrum. Using this collection of semifinite spectral triples and the product of semifinite spectral triples one can construct a mathematical tool for dimensional and zeta-function regularisation in quantum field theory.