Twisted reality and the second-order condition

TL;DR

This paper explores the second-order condition in spectral triples related to the Standard Model, proposing a twist to the reality operator J on manifolds and analyzing product behaviors.

Contribution

It introduces a twist to the reality operator J in spectral triples and examines the impact on the second-order condition and product structures.

Findings

Twist is necessary for the reality operator J to implement self-Morita equivalence.

Weakening an axiom of real spectral triples enables the twist on manifolds.

Behavior of second-order conditions under spectral triple products is characterized.

Abstract

An interesting feature of the finite-dimensional real spectral triple (A,H,D,J) of the Standard Model is that it satisfies a ``second-order'' condition: conjugation by J maps the Clifford algebra Cl_D(A) into its commutant, which in fact is isomorphic to the Clifford algebra itself (H is a self-Morita equivalence Cl_D(A)-bimodule). This resembles a property of the canonical spectral triple of a closed oriented Riemannian manifold: there is a dense subspace of H which is a self-Morita equivalence Cl_D(A)-bimodule. In this paper we argue that on manifolds, in order for the self-Morita equivalence to be implemented by a reality operator J, one has to introduce a ``twist'' and weaken one of the axioms of real spectral triples. We then investigate how the above mentioned conditions behave under products of spectral triples.