Fock Vacuum Instability and Causality

TL;DR

This paper investigates the stability of the Fock vacuum in theories with massless self-interacting fields, revealing instability in QCD and QED due to infrared effects, but stability in quantum gravity, suggesting different theoretical approaches.

Contribution

It demonstrates how infrared behavior causes vacuum instability in certain theories and proposes quantum gravity as a potentially stable effective theory.

Findings

Vacuum instability in QCD and QED due to infrared effects

Quantum gravity maintains Fock vacuum stability

Implications for treating quantum gravity as an effective theory

Abstract

The vacuum diagram is calculated at second order for theories with self-interacting massless fields in the framework of finite causal perturbation theory. It is pointed out that the infrared behaviour of the vacuum diagram leads to unstable Fock vacua for QCD or massless QED, but not for quantum gravity. Therefore a radical rearrangement of the physical system must take place for such theories. Conversely, stability of the Fock vacuum for massless interacting fields is another hint at the possibility that quantum gravity should be treated as an effective theory.