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Discrete spacetime symmetries and particle mixing in non-Hermitian scalar quantum field theories

Research output: Contribution to journalArticlepeer-review

Jean Alexandre, John Ellis, Peter Millington

Original languageUndefined/Unknown
JournalPhys. Rev. D
Published11 Jun 2020

Bibliographical note

44 pages, revtex format; to match published version, including a revised discussion of particle mixing and oscillations


  • 2006.06656v3

    2006.06656v3.pdf, 429 KB, application/pdf

    Uploaded date:18 Jan 2021

King's Authors


We discuss second quantization, discrete symmetry transformations and inner products in free non-Hermitian scalar quantum field theories with PT symmetry, focusing on a prototype model of two complex scalar fields with anti-Hermitian mass mixing. Whereas the definition of the inner product is unique for theories described by Hermitian Hamiltonians, its formulation is not unique for non-Hermitian Hamiltonians. Energy eigenstates are not orthogonal with respect to the conventional Dirac inner product, so we must consider additional discrete transformations to define a positive-definite norm. We clarify the relationship between canonical-conjugate operators and introduce the additional discrete symmetry C', previously introduced for quantum-mechanical systems, and show that the C'PT inner product does yield a positive-definite norm, and hence is appropriate for defining the Fock space in non-Hermitian models with PT symmetry in terms of energy eigenstates. We also discuss similarity transformations between PT-symmetric non-Hermitian scalar quantum field theories and Hermitian theories, showing that they would require modification in the presence of interactions. As an illustration of our discussion, we compare particle mixing in a Hermitian theory and in the corresponding non-Hermitian model with PT symmetry, showing how the latter maintains unitarity and exhibits mixing between scalar and pseudoscalar bosons.

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