Strict limit on CPT violation from gamma-ray bursts

Dec 07, 2012
IKAROS Spacecraft

Kenji Toma (Osaka Univ.), Shinji Mukohyama (Kavli IPMU, Univ. of Tokyo), Daisuke Yonetoku (Kanazawa Univ.) and their colleagues have used the photon polarization in three distant gamma-ray bursts detected by Japanese spacecraft as evidence that the polarization did not rotate during its long journey. This lack of rotation puts the most stringent constraints yet on the violation of a fundamental symmetry. This work is going to be published and highlighted in Physical Review Letters.

Photons produced by gamma-ray bursts (GRBs) that occur in the universe travel billions of light-years to reach us. This makes them excellent probes of space-time structures on extremely small scales that are being actively studied in theories.

Some quantum gravity theories, trying to unify Einstein's with , (e.g., ) predict that structures of space-time at extremely short distances may be totally different from what we think we know. On the scales treated by terrestrial experiments, the world looks exactly the same as its mirror image if the roles of particles and anti-particles are exchanged and the direction of time is reversed (i.e., CPT symmetry is conserved). If this symmetry is broken at extremely short distances, as predicted in some quantum gravity theories, polarization of photons from distant celestial objects would rotate during its long journey to us. However, several attempts to detect this rotation have come up empty, implying that nature obeys CPT at least to a level of one part in 10 million.

In this work, Toma and his colleagues have improved on these limits using data from the Japanese IKAROS spacecraft. Specifically, the on-board Gamma-ray burst Polarimeter has detected linear polarization in the gamma-ray emission of three GRBs at the most precise levels so far. This result leads to the most stringent constraint on CPT violation, a level of one part in 10^15, i.e., an improvement of 8 orders of magnitude over previous limits.

"We have confirmed that the CPT symmetry is not violated even at extremely small distances," Toma comments about the importance of this work. "This result puts a fundamental constraint on quantum gravity, a dream theory reconciling Einstein's theory of relativity and quantum theory."

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User comments : 6

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not rated yet Dec 08, 2012
This is so far off from the plank scale that it's not even funny. Once that is confirmed quantum gravity is dead.
3 / 5 (2) Dec 09, 2012
AEGIS (Antimatter experiment: Gravity, interferometry, spectroscopy)
She has a say in the too.
3.7 / 5 (3) Dec 09, 2012
We worry about future events.
Past events are deadly too.
Forced to wait and see.
Nature's irony.
vlaaing peerd
not rated yet Dec 10, 2012
Natures finest example of antialiasing on Planck scale and immediately we go dismissing some good theories. :P

Apart from string theory/QG theories shouldn't it question the existence of anything on the planck scale and therefore also parts of QM in general?
not rated yet Dec 10, 2012
The interpretation of this finding is as wrong, as the interpretation of photon delay in observations of GRB. What is measured is indeed not an absence of polarization of gamma ray bursts during their journey, because the polarization of their original source is unachievable. What is measured here is the difference in polarization of gamma ray photons of different frequency. The quantum gravity theories consider, that the low energy photons will be scattered and depolarized more, than the high energy ones. And this is actually the difference measured here.

But the Nature can employ an easy trick, how to keep the polarization of all photons in synchrony: these photons revolve itself mutually like particles in vortex ring, which travels through wast cosmic space as a single body. Therefore not only all photons will arrive to Earth in a single moment, but they all keep the same plane of polarization.
not rated yet Dec 10, 2012
The quantum gravity theories extrapolate the behavior of general relativity toward quantum mechanics at the extreme scales of distance or energy density. But the gamma ray bursts are unique with the fact, they do represents the highest energy density observable traveling at the largest distances observable. In such situation both types of QG corrections tend to compensate mutually in some aspects. This indicates the fact, the short distance or less energetic gamma ray bursts fit the QG predictions better. But the attempt to confirm such a results with their confirmation at larger distance/energy density scales not only improve the QG predictions - they wipe them all.

It corresponds the observation of ripples at the water surface, which should scatter differently in accordance to their wavelength. But when we try to observe such a scattering from largest distance, they we always get a solitons formed with mixture of wavelengths, because just such a solitons scatter in least extent.

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