Abstract
The neutral kaon system is a very peculiar system that offers unique possibilities to perform precise tests of the CPT symmetry. The entanglement of neutral kaon pairs that are produced at a ϕ-factory opens up new ways and scenarios in order to test this fundamental discrete symmetry. In this paper, the results of the most recent and significant CPT tests are reviewed. Experiments have set stringent limits on the CPT-violating parameters of different phenomenological models, some of them associated to possible decoherence mechanisms or Lorentz symmetry violation which might be justified in a quantum gravity framework. The present results show no violation of CPT symmetry, while their accuracy in some cases reaches the interesting level at which–in the most optimistic scenarios–quantum gravity effects might show up.
Highlights
Rigorous proofs of the CPT theorem (with CPT the combination of charge conjugation (C), parity (P), and time reversal (T) transformations) were provided in the 50’s by the founding Fathers of the Quantum Field Theory [1,2,3,4]
We notice that, in this case, the result is compatible with no CPT violation, while the experimental sensitivity is in the range of interest for testing quantum gravity in the most optimistic scenarios, and it could be used to loosely bound the phenomenological parameter ξand the corresponding effective quantum gravity scale MQG = MPlanck /ξ
The entanglement of neutral kaon pairs that are produced at a φ-factory represents an ideal tool to push forward these studies, and an excellent opportunity for testing the basic principles of Quantum Mechanics as well as the Lorentz symmetry
Summary
Rigorous proofs of the CPT theorem (with CPT the combination of charge conjugation (C), parity (P), and time reversal (T) transformations) were provided in the 50’s by the founding Fathers of the Quantum Field Theory [1,2,3,4] ( see Refs. [5,6,7] for some recent developments). The theorem ensures that exact CPT invariance holds for any quantum field theory that is formulated on flat space-time while assuming (1) Lorentz invariance, (2) Locality, and (3) Unitarity (i.e., conservation of probability). This theorem constitutes one of the most important results at the foundation of relativistic quantum field theory. On the surface, the two theorems appear to involve completely different subjects, they are, intimately linked, and both deeply connected to space-time symmetries [8,9] The latter constitutes an additional confirmation that testing the validity of CPT invariance means probing the most fundamental assumptions underpinning the Standard Model of elementary particles and their interactions.
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