Modern searches for Lorentz violation
These models introduce Lorentz and CPT violations through spontaneous symmetry breaking caused by hypothetical background fields, resulting in some sort of preferred frame effects.
No Lorentz violations have been measured thus far, and exceptions in which positive results were reported have been refuted or lack further confirmations.
[3] In addition, a series of test theories of special relativity and effective field theories (EFT) for the evaluation and assessment of many experiments have been developed, including: However, the Standard-Model Extension (SME) in which Lorentz violating effects are introduced by spontaneous symmetry breaking, is used for most modern analyses of experimental results.
[12] Many terrestrial experiments have been conducted, mostly with optical resonators or in particle accelerators, by which deviations from the isotropy of the speed of light are tested.
In modern variants of the Michelson–Morley experiment, the dependence of light speed on the orientation of the apparatus and the relation of longitudinal and transverse lengths of bodies in motion is analyzed.
Also modern variants of the Kennedy–Thorndike experiment, by which the dependence of light speed on the velocity of the apparatus and the relation of time dilation and length contraction is analyzed, have been conducted; the recently reached limit for Kennedy-Thorndike test yields 7 10−12.
In addition, the Standard-Model Extension (SME) can be used to obtain a larger number of isotropy coefficients in the photon sector.
related one-way light speed isotropy in combination with the electron sector of the SME was conducted by Bocquet et al.
[17] They searched for fluctuations in the 3-momentum of photons during Earth's rotation, by measuring the Compton scattering of ultrarelativistic electrons on monochromatic laser photons in the frame of the cosmic microwave background radiation, as originally suggested by Vahe Gurzadyan and Amur Margarian [18] (for details on that 'Compton Edge' method and analysis see,[19] discussion e.g.[20]).
[44] However, since these measurements are based on the assumption that the speed of light is constant, they can also be used as tests of special relativity by analyzing potential distance and orbit oscillations.
For instance, Zoltán Lajos Bay and White (1981) demonstrated the empirical foundations of the Lorentz group and thus special relativity by analyzing the planetary radar and LLR data.
One possibility is to investigate otherwise forbidden effects at threshold energy in connection with particles having a charge structure (protons, electrons, neutrinos).
Depending on which of these particles travels faster or slower than the speed of light, effects such as the following can occur:[77][78] Since astronomic measurements also contain additional assumptions – like the unknown conditions at the emission or along the path traversed by the particles, or the nature of the particles –, terrestrial measurements provide results of greater clarity, even though the bounds are wider (the following bounds describe maximal deviations between the speed of light and the limiting velocity of matter): By this kind of spectroscopy experiments – sometimes called Hughes–Drever experiments as well – violations of Lorentz invariance in the interactions of protons and neutrons are tested by studying the energy levels of those nucleons in order to find anisotropies in their frequencies ("clocks").
[90] Such experiments are currently the most sensitive terrestrial ones, because the precision by which Lorentz violations can be excluded lies at the 10−33 GeV level.
[16] Chou et al. (2010) even managed to measure a frequency shift of ~10−16 due to time dilation, namely at everyday speeds such as 36 km/h.
For instance, Altschul (2007) placed upper limits on Lorentz violation of the tau of 10−8, by searching for anomalous absorption of high energy astrophysical radiation.
They showed that the cross section production of these pairs doesn't depend on sidereal time during Earth's rotation.
[138] They showed that differential cross sections for the vector and axial couplings in QED become direction dependent in the presence of Lorentz violation.
The standard framework for such investigations is the Parameterized post-Newtonian formalism (PPN), in which Lorentz violating preferred frame effects are described by the parameters
level by examining Keplerian orbital elements of a test particle acted upon by Lorentz-violating gravitomagnetic accelerations.
[141] Xie (2012) analyzed the advance of periastron of binary pulsars, setting limits on Lorentz violation at the
[143] Additionally, a series of investigations have been published in which a sidereal dependence of the occurrence of neutrino oscillations was tested, which could arise when there were a preferred background field.
Direct velocity measurements indicated an upper limit for relative speed differences between light and neutrinos of
[9] In 2001, the LSND experiment observed a 3.8σ excess of antineutrino interactions in neutrino oscillations, which contradicts the standard model.
[160] First results of the more recent MiniBooNE experiment appeared to exclude this data above an energy scale of 450 MeV, but they had checked neutrino interactions, not antineutrino ones.
[163][164] Whether those anomalies can be explained by sterile neutrinos, or whether they indicate Lorentz violations, is still discussed and subject to further theoretical and experimental researches.
[168][169][170] However, in 2011 MINOS updated their antineutrino results; after evaluating additional data, they reported that the difference is not as great as initially thought.
[172] In 2007, the MAGIC Collaboration published a paper, in which they claimed a possible energy dependence of the speed of photons from the galaxy Markarian 501.
[52][173] However, the MAGIC result was superseded by the substantially more precise measurements of the Fermi-LAT group, which couldn't find any effect even beyond the Planck energy.
In 1997, Nodland & Ralston claimed to have found a rotation of the polarization plane of light coming from distant radio galaxies.
