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New Ways Suggested to Probe Lorentz Violation

Lorentz invariance, a basic building block of relativity, holds that the laws of physics remain the same for observers traveling at constant speeds relative to each other, or rotated with respect to each other. Some theoretical models, called standard model extensions, have predicted violations of Lorentz symmetry. At the April Meeting, several theorists reported on ways Lorentz violation might turn up in various experiments.   

“All of known physics depends on Lorentz symmetry,” Matt Mewes of Marquette University said in a press conference at the April Meeting. If that symmetry is not exact, there will be some small defects in everything else. He likened Lorentz symmetry to a building block on which much of the rest of physics rests. If the Lorentz symmetry block was slightly chipped, the whole structure on top of it would lean slightly. So by making very precise measurements of many different physical phenomena, one could expect to see evidence of Lorentz violation.

One way to look for Lorentz violation is in the cosmic microwave background polarization, Mews suggested. Recent experiments have measured the polarization of the CMB at different positions in the sky. An unexpected twist in that polarization would indicate a breakdown of relativity. Mews, in collaboration with Alan Kostelecky of Indiana University, analyzed data from the CMB experiment BOOMERANG, looking at many different parameters. They found that the results hint slightly at a potential unexpected twist in the polarization. Future experiments will be needed to verify this. The CMB polarization is a good way to look for relativity violations because the longer light travels, the more chance it has to undergo this slight rotation, said Mews. No other light has traveled further than the CMB.

Jay Tasson of Indiana University described another way to look for violations of general relativity. Torsion is a warping of space and time in addition to the curvature of spacetime that Einstein’s general relativity predicts. Such a warping, predicted by some alternative theories of gravity, would cause particles’ spins to precess. A University of Washington experiment used a large number of electron spins to detect these effects. A complementary approach by a Harvard group used microwaves emitted by a helium-xenon maser to measure changes in the spin orientation of neutrons. Tasson and Kostelecky used these measurements to determine limits on 15 of the 24 quantities that would describe torsion. So far, no evidence of torsion has been observed in these extremely sensitive measurements, Tasson reported.  

Still another place to look for Lorentz violation is by searching for tiny variations in the moon’s orbit about the earth. Quentin Bailey of Embry-Riddle Aeronautical University described how researchers looked at data from a laser ranging experiment that bounced lasers off mirrors placed on the moon by astronauts. The scientists used that data to measure parameters that would reveal any deviation from general relativity. In addition, another experiment, performed at Stanford, tracked the gravitational force felt by atoms very accurately, looking for tiny deviations from what general relativity predicts. These experiments are all very sensitive, to several parts in ten billion. All measurements were consistent with general relativity, Bailey reported.

Although no solid evidence of Lorentz violation has been found so far in any experiment, there is still room for ever more sensitive experiments to search for the effect, the researchers said.

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