Noncommutative spectral geometry: A guided tour for theoretical physicists

TL;DR

This paper reviews a noncommutative geometric approach to unifying gravity with the standard model, highlighting the mathematical structure, physical implications, and potential cosmological applications of the spectral action principle.

Contribution

It introduces a geometric model based on noncommutative geometry that naturally incorporates the standard model and gravity, with insights into quantization and cosmology.

Findings

The model reproduces the standard model coupled to gravity.

Doubling of the algebra relates to dissipation and gauge structure.

Potential implications for inflation and cosmological evolution.

Abstract

We review a gravitational model based on noncommutative geometry and the spectral action principle. The space-time geometry is described by the tensor product of a four-dimensional Riemanian manifold by a discrete noncommutative space consisting of only two points. With a specific choice of the finite dimensional involutive algebra, the noncommutative spectral action leads to the standard model of electroweak and strong interactions minimally coupled to Einstein and Weyl gravity. We present the main mathematical ingredients of this model and discuss their physical implications. We argue that the doubling of the algebra is intimately related to dissipation and the gauge field structure. We then show how this noncommutative spectral geometry model, a purely classical construction, carries implicit in the doubling of the algebra the seeds of quantization. After a short review on the phenomenological consequences of this geometric model as an approach to unification, we discuss some of its cosmological consequences. In particular, we study deviations of the Friedmann equation, propagation of gravitational waves, and investigate whether any of the scalar fields in this model could play the role of the inflaton.