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Shlomo Sternberg (math professor at Harvard) wrote a book called "Group theory and physics". On p156 (link) there's a strange offhand comment:

"Experiments done in 1964 by Fitch and Cronin seem to indicate that CP is not conserved. I do not fully understand the issues involved in the correct interpretation of this experiment, which clearly shows that CP and CPT are not both conserved. It follows from the locality axioms, that quantum field theory implies that CPT is a symmetry of nature, and hence that CP is violated in the Fitch-Cronin experiment. But other, group theoretical, hypotheses might favor CP. I have my own views on the subject, which I will not expand on in this book."

I cannot find any other publication where Prof. Sternberg elaborated his views on this. But he obviously suspects that CP is an exact symmetry while CPT is not.

So the question is: (1) Does the Fitch-Cronin experiment (or any other) disprove CP? Or does it only "show that CP and CPT are not both conserved"? (2) If the latter, is it remotely plausible that CPT is false? (How universal is the CPT theorem? Does it hold even in string theory?)

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OK, I just found this PDG review. I don't understand the details but here's my impression: CP-violation and CPT-violation both affect kaon decay but with different experimental signatures; people have measured both independently; the CPT-violation is zero while the CP-violation is nonzero. Can anyone confirm that I'm understanding this properly? Thanks! – Steve B Jun 2 '11 at 7:11

CPT is a general theorem of quantum field theories:

Specifically, the CPT theorem states that any Lorentz invariant local quantum field theory with a Hermitian Hamiltonian must have CPT symmetry.

Questioning CPT invariance is questioning the foundations of modern physics theory, which is probably the reason you cannot find anything on this. The label "crackpot" is easily stuck on theories denying Lorenz invariance, for example, because is is founded on solid experimental evidence. Hermitian Hamiltonians describe the plethora of physics data and are a basis of the quantum mechanical description of nature. Locality is also a sine qua non in mainstream physics theory.

There are now a number of experiments showing CP violation, {a particle is interchanged with its antiparticle (C symmetry), and left and right is swapped (P symmetry).}, not needing to invoke the CPT theorem, except to point out that time reversal does not hold for these reactions.

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Plus one, Anna! ;-) – Luboš Motl Jun 2 '11 at 8:49
My main question was, Do the CP-violation experiments actually prove "CP violation" or just "CP or CPT violation". Your response is, "a number of experiments show CP violation", and you link to the wikipedia article on CP-violating experiments. This isn't helpful: My main question is whether these experiments were interpreted correctly. Is the CPT assumption necessary or not? Even if we're 100% confident in CPT, I can still ask "Is the assumption of CPT a part of the experimental data analysis?" Have you worked through the details of the experiment to confirm that CPT is not involved? – Steve B Jun 2 '11 at 17:04

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