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Indications against Dynamical CPT Symmetry Restoration in Quantum Gravity

Astrid Eichhorn*

Marc Schiffer†

  • Institute for Theoretical Physics, Heidelberg University, Philosophenweg 16, 69120 Heidelberg, Germany

  • High Energy Physics Department, Institute for Mathematics, Astrophysics, and Particle Physics, Radboud University, Nijmegen, The Netherlands

  • *Contact author: eichhorn@thphys.uni-heidelberg.de
  • †Contact author: marc.schiffer@ru.nl
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Phys. Rev. Lett. 136, 091501 – Published 6 March, 2026

DOI: https://doi.org/10.1103/frd8-pg3d

Abstract

CPT symmetry is at the heart of the standard model of particle physics and experimentally very well tested, but expected to be broken in some approaches to quantum gravity. It thus becomes pertinent to explore which of the two alternatives is realized: (i) CPT symmetry is emergent, so that it is restored in the low-energy theory, even if it is broken beyond the Planck scale, (ii) CPT symmetry cannot be emergent and must be fundamental, so that any approach to quantum gravity, in which CPT is broken, is ruled out. We explore this by calculating the renormalization group flow of CPT-violating interactions under the impact of quantum fluctuations of the metric. We find that CPT symmetry cannot be emergent and conclude that quantum-gravity approaches must avoid the breaking of CPT symmetry. As a specific example, we discover that in asymptotically safe quantum gravity CPT symmetry remains intact, if it is imposed as a fundamental symmetry, but it is badly broken at low energies if a tiny amount of CPT violation is present in the transplanckian regime.

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Phys. Rev. Lett. 136, 091501– Published 6 March, 2026
  • Received 2 July 2025
  • Revised 11 December 2025
  • Accepted 30 January 2026
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