The cosmological CPT theorem, by Harry Goodhew, Ayngaran Thavanesan, Aron C. Wall

SciPost Physics Home Authoring Refereeing Submit a manuscript About The cosmological CPT theorem Harry Goodhew, Ayngaran Thavanesan, Aron C. Wall SciPost Phys. 20, 049 (2026) · published 18 February 2026 doi: 10.21468/SciPostPhys.20.2.049 pdf BiBTeX RIS Submissions/Reports Abstract The CPT theorem states that a unitary and Lorentz-invariant theory must also be invariant under a discrete symmetry CRT which reverses charge, time, and one spatial direction. In this article, we study a $\mathbb{Z}_2 × \mathbb{Z}_2$ symmetry group, in which two of the non-trivial symmetries ("Reflection Reality" and a 180 degree rotation) are implied by Unitarity and Lorentz Invariance respectively, while the third is CRT. (In cosmology, Scale Invariance plays the role of Lorentz Invariance.) This naturally leads to converses of the CPT theorem, as any two of the discrete $\mathbb{Z}_2$ symmetries will imply the third one. Furthermore, in many field theories, the Reflection Reality $\mathbb{Z}_2$ symmetry is actually sufficient to imply the theory is fully unitary, over a generic range of couplings. Building upon previous work on the Cosmological Optical Theorem, we derive non-perturbative reality conditions associated with bulk Reflection Reality (in all flat FLRW models) and CRT (in de Sitter spacetime), in arbitrary dimensions. Remarkably, this CRT constraint suffices to fix the phase of all wavefunction coefficients at future infinity (up to a real sign) — without requiring any analytic continuation, or comparison to past infinity — although extra care is required in cases where the bulk theory has logarithmic UV or IR divergences. This result has significant implications for de Sitter holography, as it allows us to determine the phases of arbitrary $n$-point functions in the dual CFT. × TY - JOURPB - SciPost FoundationDO - 10.21468/SciPostPhys.20.2.049TI - The cosmological CPT theoremPY - 2026/02/18UR - https://scipost.org/SciPostPhys.20.2.049JF - SciPost PhysicsJA - SciPost Phys.VL - 20IS - 2SP - 049A1 - Goodhew, HarryAU - Thavanesan, AyngaranAU - Wall, Aron C.AB - The CPT theorem states that a unitary and Lorentz-invariant theory must also be invariant under a discrete symmetry CRT which reverses charge, time, and one spatial direction. In this article, we study a $\mathbb{Z}_2 × \mathbb{Z}_2$ symmetry group, in which two of the non-trivial symmetries ("Reflection Reality" and a 180 degree rotation) are implied by Unitarity and Lorentz Invariance respectively, while the third is CRT. (In cosmology, Scale Invariance plays the role of Lorentz Invariance.) This naturally leads to converses of the CPT theorem, as any two of the discrete $\mathbb{Z}_2$ symmetries will imply the third one. Furthermore, in many field theories, the Reflection Reality $\mathbb{Z}_2$ symmetry is actually sufficient to imply the theory is fully unitary, over a generic range of couplings. Building upon previous work on the Cosmological Optical Theorem, we derive non-perturbative reality conditions associated with bulk Reflection Reality (in all flat FLRW models) and CRT (in de Sitter spacetime), in arbitrary dimensions. Remarkably, this CRT constraint suffices to fix the phase of all wavefunction coefficients at future infinity (up to a real sign) — without requiring any analytic continuation, or comparison to past infinity — although extra care is required in cases where the bulk theory has logarithmic UV or IR divergences. This result has significant implications for de Sitter holography, as it allows us to determine the phases of arbitrary $n$-point functions in the dual CFT.ER - × @Article{10.21468/SciPostPhys.20.2.049, title={{The cosmological CPT theorem}}, author={Harry Goodhew and Ayngaran Thavanesan and Aron C. Wall}, journal={SciPost Phys.}, volume={20}, pages={049}, year={2026}, publisher={SciPost}, doi={10.21468/SciPostPhys.20.2.049}, url={https://scipost.org/10.21468/SciPostPhys.20.2.049},} Ontology / Topics See full Ontology or Topics database. Correlation functions Cosmic microwave background (CMB) Dualities Expansion of the Universe Gravity Holography Mirror symmetry Parity symmetry Quantum field theory (QFT) Quantum gravity Time-reversal symmetry de Sitter space Authors / Affiliations: mappings to Contributors and Organizations See all Organizations. 1 2 Harry Goodhew, 1 3 Ayngaran Thavanesan, 1 4 Aron C. Wall 1 University of Cambridge 2 National Taiwan University [NTU] 3 Kavli Institute for Theoretical Physics [KITP] 4 Institute for Advanced Study [IAS] Funders for the research work leading to this publication Air Force Office of Scientific Research [AFOSR] Heising-Simons Foundation Isaac Newton Trust Kavli Institute for Theoretical Physics, University of California, Santa Barbara (through Organization: Kavli Institute for Theoretical Physics [KITP]) Ministry of Education National Science Foundation [NSF] Science and Technology Facilities Council [STFC] Simons Foundation University of Cambridge