Synopsis: Distant Bursts Show no Signs of Predicted Light Rotation

Cosmic gamma-ray bursts turn out to be polarized, which rules out the breaking of a fundamental symmetry down to the lowest limits ever observed.
Synopsis figure
Courtesy of the Japanese Aerospace Exploration Agency (JAXA)

Gamma rays from cosmic explosions travel billions of light years to reach us. This makes them excellent probes of extremely small irregularities in the fabric of spacetime, as predicted by some quantum gravity theories. Along these lines, researchers have used the detection of polarization in three distant gamma-ray bursts (GRBs) as evidence that the light did not rotate during its long journey. As described in Physical Review Letters, this lack of rotation puts the most stringent constraints yet on the violation of a fundamental symmetry.

Attempts to unify gravity with quantum mechanics often predict small variations to the laws of relativity. This can open the door to violating CPT, which is a symmetry that relates antimatter, mirror reflections, and the arrow of time. One consequence of CPT breaking would be a speed difference between photons of one polarization and another, observable through an energy-dependent rotation of light traveling through space. 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.

Kenji Toma of Osaka University in Japan and his colleagues have improved on these limits using data from the Japanese IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) spacecraft. Specifically, the on-board gamma-ray burst polarimeter (GAP) has detected linear polarization in the gamma-ray emission of three GRBs. This polarization could only be observed if CPT is respected down to a level of one part in 1015, an improvement of eight orders of magnitude over previous model-independent limits. – Michael Schirber


Announcements

More Announcements »

Subject Areas

Particles and FieldsAstrophysics

Previous Synopsis

Next Synopsis

Biological Physics

Paddling in Sync

Read More »

Related Articles

Synopsis: Anisotropy Limits for the Universe
Cosmology

Synopsis: Anisotropy Limits for the Universe

A new study of the cosmic microwave background places the strictest limits to date on a rotating Universe and other forms of cosmic anisotropy. Read More »

Synopsis: Spotting Dark Matter with Supermaterials
Particles and Fields

Synopsis: Spotting Dark Matter with Supermaterials

Superconducting aluminum or superfluid helium could be used to detect superlight dark matter particles. Read More »

Synopsis: Strange Mesonic Atoms Detected
Particles and Fields

Synopsis: Strange Mesonic Atoms Detected

The DIRAC collaboration at CERN reports the first statistically significant observation of an atom formed from a 𝜋 meson and a K meson. Read More »

More Articles