Astronomers have probed the Perseus galaxy cluster in search of an (so far) undetected particle that would help to support string theory.
String theory is the idea that all known forces, particles and interactions can be connected through a single framework to understand the physical universe. A team of astronomers using NASA's Chandra X-ray Observatory studied galaxy clusters — the largest structures in the universe held together by gravity — for signs of an ultra-low-mass particle called an axion, which many models of string theory predict should exist.
"While it may sound like a long shot to look for tiny particles like axions in gigantic structures like galaxy clusters, they are actually great places to look," David Marsh, co-author of the study from Stockholm University in Sweden, said in a statement from the Chandra X-ray Observatory.
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Axion particles are believed to have incredibly low masses, potentially ranging from a millionth of the mass of an electron down to zero mass. The team also looked for signs of "axion-like particles," which are a broader class of ultra-low-mass particles with similar properties to axions, according to the statement.
Additionally, these ultra-low-mass particles may sometimes convert into photons — the particles that make up light — when they pass through magnetic fields. In turn, photons may also convert into axions under certain conditions. Both scenarios depend on the mass of the particles and how easily they can make the conversion, also known as convertibility, according to the statement.
As part of this new study, astronomers using the Chandra space telescope studied the spectrum of X-ray emissions produced by material falling towards the supermassive black hole at the center of the Perseus galaxy cluster.
"Galaxy clusters contain magnetic fields over giant distances, and they also often contain bright X-ray sources," Marsh said in the statement. "Together these properties enhance the chances that conversion of axion-like particles would be detectable."
However, the team did not detect any distortions in the X-ray emissions that would indicate axion-like particles were present, according to the statement.
"Our research doesn't rule out the existence of these particles, but it definitely doesn't help their case," Helen Russell, co-author of the study from the University of Nottingham in the UK, said in the statement. "These constraints dig into the range of properties suggested by string theory, and may help string theorists weed their theories."
One possible explanation for these recent observations is that the particles have either a lower or higher convertibility than the Chandra space telescope is able to detect, the researchers said.
"Until recently I had no idea just how much X-ray astronomers bring to the table when it comes to string theory, but we could play a major role," Christopher Reynolds, lead author of the study from the University of Cambridge in the United Kingdom, said in the statement. "If these particles are eventually detected it would change physics forever."
Their findings were published Feb. 10 in The Astrophysical Journal.
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There is a convergence of problems for extensions of our current quantum field theory for particles, such as these. Axions in of itself would solve the so called strong CP problem of why quarks are not part of the particles that give the universe matter, it looks like neutrinos are but why not some of both? And supersymmetry axion-like particles are generic for string extensions of the standard model of particles.
But there are many results that fail to turn up axions or axion-like particles, such as nuclear spin measurements or gamma ray spectra of galaxies https://www.forbes.com/sites/briankoberlein/2020/03/22/astronomers-rule-out-a-theory-of-everything/#516194464f6a ]. And now X-ray emissions from galaxy clusters.
Here they join experiments of particle collisions in LHC and electron sphericity in ACME in making string theory - as well as axions - much less appetizing. If absence of natural energy scale WIMPs in LHC and ACME count as rejecting strings, absence of natural consequence axion/axion-like particles counts too.
And so it counts as absence of a solution for the strong CP finetuning. Some of the references to the new work describes the strong CP as *very* finetuned if axions or something similar do not exist. (Technically and AFAIU those technicalities, cancellation of non-linearity causing CP asymmetry happens up to order 14 in quark field theory. There is some CP asymmetry among quarks and gluons, but it is virtually zero in comparison to what is needed for having matter.)
Instead of the notion that something must be added to our current quantum field theory for particles, I note that inflation excel in solving such apparent finetuning in the same way that it solves for finetuning the amount of dark energy.
So instead of finetuning cancellations, it is easier to think that when the universe cooled down and putatively the fields froze out by way of non-linear phase transitions, it was a coin toss whether quarks or neutrinos would have the chirality asymmetry that solves the CP asymmetry for having matter. In our universe it was the neutrinos.
A key statement is made in this report concerning the test(s) ""After all this time and effort, no evidence for ALPs was found."
QFT, String Theory, inflation field(s), inflatons, magnetic monopoles, etc. The list is abundant and needs a complete, documented list of all the exotic particles created that are tested or not confirmed - published that the cosmology department invokes to explain the origin of everything. There is 1E+200,000 Calabi-Yao manifolds reported by space.com, 10 or 11 dimensions and 1E+200 curls for strings too. In astronomy, I can see the Galilean moons orbiting Jupiter using my telescopes and so far, tests do not show strings or many dimensions that the light passes through to reach my telescopes when I view but the finite speed of light was determined at Jupiter in the 1670s using telescope observations of the moons and eclipse events. This latest effort to find axion like particles (ALPs), not axions, did not confirm their existence in nature.