Standard Model Extension
Another, more extensive, model is the Standard Model Extension (SME) by Alan Kostelecký and others. Contrary to the Roberson-Mansouri-Sexl (RMS) framework, which is kinematic in nature and restricted to special relativity, SME not only accounts for special relativity, but for dynamical effects of the standard model and general relativity as well. It investigates possible spontaneous breaking of both Lorentz invariance and CPT symmetry. RMS is fully included in SME, though the latter has a much larger group of parameters that can indicate any Lorentz or CPT violation.
For instance, a couple of SME parameters was tested in a 2007 study sensitive to 10-16. It employed two simultaneous interferometers over a year's observation: Optical in Berlin at 52°31'N 13°20'E and microwave in Perth at 31°53'S 115°53E. A preferred background (leading to Lorentz Violation) could never be at rest relative to both of them. A large number of other tests has been carried out in recent years, such as the Hughes–Drever experiments. A list of derived and already measured SME-values was given by Kostelecký and Russell.
Read more about this topic: Test Theories Of Special Relativity
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