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- Covariant quantization of CPT-violating photonsPublication . Colladay, D.; McDonald, P.; Noordmans, J. P.; Potting, RobertusWe perform the covariant canonical quantization of the CPT - and Lorentz-symmetry-violating photon sector of the minimal Standard-Model Extension, which contains a general (timelike, lightlike, or spacelike) fixed background tensor k(AF)(u). Well-known stability issues, arising from complex-valued energy states, are solved by introducing a small photon mass, orders of magnitude below current experimental bounds. We explicitly construct a covariant basis of polarization vectors, in which the photon field can be expanded. We proceed to derive the Feynman propagator and show that the theory is microcausal. Despite the occurrence of negative energies and vacuum-Cherenkov radiation, we do not find any runaway stability issues, because the energy remains bounded from below. An important observation is that the ordering of the roots of the dispersion relations is the same in any observer frame, which allows for a frame-independent condition that selects the correct branch of the dispersion relation. This turns out to be critical for the consistency of the quantization. To our knowledge, this is the first system for which quantization has consistently been performed, in spite of the fact that the theory contains negative energies in some observer frames.
- Lorentz and CPT violationPublication . Potting, Robertus; Branco, GC; EmmanuelCosta, D; Felipe, RG; Joaquim, FR; Lavoura, L; PalomaresRuiz, S; Rebelo, MN; Romao, JC; Silva, JP; SilvaMarcos, JIDuring the past two decades there has been a growing interest in the possibility that Lorentz and/or CPT might not be exact symmetries of Nature. In this short review, we present the current state of affairs, addressing both theoretical and experimental/observational issues. We pay particular attention to the role that has been played by the so-called Standard Model Extension