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In all known space, between stars and galaxies, an extremely faint glow pervades, a relic left behind by the dawn of the Universe. This is the microwave cosmic background (CMB), the first light that could travel through the Universe when it cooled sufficiently about 380,000 years after the Big Bang for the ions and electrons to combine into atoms.
But now scientists have discovered something peculiar about CMB. A new measurement technique has revealed evidence of torsion in the light – which could be indicative of a violation of parity symmetry, hinting at physics outside the Standard Model.
According to the Standard Model of physics, if we were to turn the Universe upside down as if it were a mirror of itself, the laws of physics would hold. Subatomic interactions should occur in exactly the same way in the mirror as in the real universe. This is called parity symmetry.
As far as we have been able to measure so far, there is only one fundamental interaction that breaks the parity symmetry; it is the weak interaction between the subatomic particles which is responsible for the radioactive decay. But finding another place where parity symmetry breaks down could lead us to new physics beyond the Standard Model.
And two physicists – Yuto Minami from the High Energy Accelerator Research Organization in Japan; and Eiichiro Komatsu of the Max Planck Institute for Astrophysics in Germany and the Kavli Institute for Physics and Mathematics of the Universe in Japan – believe they have found clues to this in the polarization angle of the CMB.
Polarization occurs when light is scattered, causing its waves to propagate in a certain orientation.
Reflective surfaces such as glass and water polarize light. You are probably familiar with polarized sunglasses, which are designed to block certain orientations to reduce the amount of light reaching the eye.
Even water and particles in the atmosphere can scatter and polarize light; a rainbow is a good example.
The first Universe, for the first 380,000 years or so, was so hot and dense that atoms could not exist. Protons and electrons flew like ionized plasma, and the Universe was opaque, like thick smoky fog.
It wasn’t until the Universe cooled down enough for these protons and electrons to combine into a neutral gas, the hydrogen atoms, that space became clear, allowing photons to travel freely.
During the transition from ionized plasma to neutral gas, the photons scattered over the electrons, causing the CMB to polarize. The polarization of the CMB can tell us a lot about the Universe. Especially if it is turned at an angle.
This angle, described as β, could indicate a CMB interaction with dark matter or dark energy, the mysterious inner and outer forces that seem to dominate the Universe, but which we cannot directly detect.
(Y. Minami / KEK)
“If dark matter or dark energy interacts with light from the microwave cosmic background in a way that violates parity symmetry, we can find its signature in the polarization data,” Minami explained.
The problem with identifying β with certainty lies in the technology we use to detect the polarization of the CMB. The European Space Agency’s Planck satellite, which published its most recent CMB observations in 2018, is equipped with polarization-sensitive detectors.
But unless you know exactly how these detectors are oriented relative to the sky, it’s impossible to tell if what you are looking at is actually β, or a spin in the detector that just looks like β.
The team’s technique relies on studying a different source of polarized light and comparing the two to extract the false signal.
“We have developed a new method to determine artificial rotation using polarized light emitted by dust in our Milky Way,” Minami said. “With this method, we have achieved twice the accuracy of previous work, and are finally able to measure β.”
The Milky Way’s radiation sources are much closer than the CMB, so they are unaffected by dark matter or dark energy. Any rotation of the polarization should therefore only result from a rotation of the detector.
The CMB is affected by both β and artificial rotation – so if you subtract the artificial rotation observed in the Milky Way sources from the observations of the CMB, you should only be left with β.
Using this technique, the team determined that β is non-zero, with 99.2% certainty. Sounds high enough, but it’s still not enough to claim a discovery of new physics. For this, a confidence level of 99.99995% is required.
But the discovery certainly demonstrates that CMB deserves further study.
“It is clear that we have yet to find definitive evidence for new physics; higher statistical significance is needed to confirm this signal,” said astrophysicist Eiichiro Komatsu of the Kavli Institute for Physics and Physics. mathematics of the universe.
“But we are excited because our new method finally allowed us to make this measurement ‘impossible’, which may indicate new physics.”
The research was published in Physical examination letters.
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