Using the polarization data from ESA’s Planck satellite, a mission that have studied the Cosmic Microwave Background (CMB), the oldest light in the Universe, a duo of astrophysicists has uncovered intriguing signs of new physics beyond the Standard Model of elementary particles and fields.

As the CMB light (left image) travels through the Universe until observed on Earth (right image), the direction in which the electromagnetic wave oscillates (orange line) is rotated by the angle β; the rotation could be caused by dark matter or dark energy interacting with the CMB light, which changes the patterns of polarization (black lines inside the images); the red and blue regions in the images show hot and cold regions of the CMB, respectively. Image credit: Y. Minami / KEK.

As the CMB light (left image) travels through the Universe until observed on Earth (right image), the direction in which the electromagnetic wave oscillates (orange line) is rotated by the angle β; the rotation could be caused by dark matter or dark energy interacting with the CMB light, which changes the patterns of polarization (black lines inside the images); the red and blue regions in the images show hot and cold regions of the CMB, respectively. Image credit: Y. Minami / KEK.

“The laws of physics governing the Universe are thought not to change when flipped around in a mirror,” said Dr. Yuto Minami from Japan’s High Energy Accelerator Research Organization and Dr. Eiichiro Komatsu from the Kavli Institute for the Physics and Mathematics of the Universe and the Max Planck Institute for Astrophysics.

“For example, electromagnetism works the same regardless of whether you are in the original system, or in a mirrored system in which all spatial coordinates have been flipped.”

“If this symmetry, called parity, is violated, it may hold the key to understanding the elusive nature of dark matter and dark energy, which occupy 25 and 70% of the energy budget of the Universe today, respectively.”

“While both dark, these two components have opposite effects on the evolution of the Universe: dark matter attracts, while dark energy causes the Universe to expand ever faster.”

The researchers found hints of a violation of parity symmetry in the CMB radiation.

“The CMB light initially became polarized when scattered by electrons 400,000 years after the Big Bang,” they said.

“As this light traveled through the Universe for 13.8 billion years, its interaction with dark matter or dark energy could cause the plane of polarization to rotate by an angle β.”

“If dark matter or dark energy interact with the CMB light in a way that violates parity symmetry, we can find its signature in the polarization data,” Dr. Minami said.

To measure the rotation angle β, the team needed polarization-sensitive detectors, such as those onboard the Planck satellite, and needed to know their absolute polarization angles.

“We developed a new method to determine the artificial rotation using the polarized light emitted by dust in our Milky Way,” Dr. Minami said.

“With this method, we achieved a precision that is twice that of the previous work, and are finally able to measure β.”

“The distance traveled by the light from dust within the Milky Way is much shorter than that of the CMB,” the scientists said.

“This means that the dust emission is not affected by dark matter or dark energy, i.e. β is present only in the CMB light, while the artificial rotation affects both.”

“The difference in the measured polarization angle between both sources of light can thus be used to measure β.”

Using their new method, the astrophysicists found the angle β to be 0.35 deg, which excludes β=0 with 99.2% confidence level.

“It is clear that we have not found definitive evidence for new physics yet — higher statistical significance is needed to confirm this signal,” Dr. Komatsu said.

“But we are excited because our new method finally allowed us to make this ‘impossible’ measurement, which may point to new physics.”

The results appear in the journal Physical Review Letters.

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Yuto Minami & Eiichiro Komatsu. 2020. New Extraction of the Cosmic Birefringence from the Planck 2018 Polarization Data. Phys. Rev. Lett 125 (22): 221301; doi: 10.1103/PhysRevLett.125.221301