Dark Matter Decoding: Why Axions Could Solve Our Universe’s Greatest Mystery

by Barbara R. Abercrombie
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Physics is permeated with riddles, which keeps the field going. These mind-bending puzzles promote a race to the truth. But of all the dilemmas, I would say that two undoubtedly fall under Priority A. First, when scientists look at the sky, they constantly see stars and galaxies traveling further from our planet and away from each othe in all directions. The Universe seems like a bubble that blows up, and that’s how we discovered it’s expanding. But something isn’t right.

This brings us to problem two. Space doesn’t seem to have enough stuff — stars, particles, planets, and everything else — to blow up so quickly. In other words, the Universe is expanding much faster than our physics says it can, and it’s even picking up speed as you read this,w

According to the best calculations of experts, galaxies spin so incredibly fast with everything turning that we would expect the spirals to behave like out-of-control carousels, knocking metal horses off the ride. Yet the Milky Way is not drifting apart. There doesn’t seem to be enough material in the Universe to anchor them together.

So what’s going on?

A simulation of dark matter filaments through the Universe.

Zarija Lukic/Lawrence Berkeley National LaboratoryIns general terms, physicists call “missing” things that push the cosmos out dark energy and pieces that hold galaxies together — presumably in a halo-like shape — dark matter. Neither interacts with light or value we can see, so they are invisible. They combined Dark case and up to 95% of the Universe.

The authors of a recent review published in the journal Science Advances elaborate on dark matter, writing that “it may well consist of one or more kinds of fundamental particles … invisible form of matter, such as black holes.”

Black holes or not, dark matter is elusive. To decipher its secrets, scientists have picked a handful of suspects from the cosmic lineup, and one of the most sought-after particles is a strange little speck called the axion.

The wide-open hypothesis of axions

You may have heard of the Standard Model, which is pretty much the holy grail, an ever-growing textbook of particle physics. It outlines how every single particle in the Universe works.

However, the Science Advances review points out that some “particle physicists are restless and dissatisfied with the Standard Model because it has many theoretical shortcomings and leaves many pressing experimental questions unanswered.” More specifically,s, it leads directly to a paradox regarding a well-established scientific concept called CPT invariance. Ah, the physics puzzles continue.

Milky way and associated dark matter halo, illustration.

Mark Garlick/Science Photo Libra

In short, CPT invariance states that the Universe must be symmetric when it comes to C (charge), P (parity), and T (time). If everything had the opposite direction, being left-handed instead of right-handed, and traveling backward through time instead of forward, then the Universe should stay the same. For that reason, it is also called CPT symmetry.

For a long time, CPT symmetry seemed unbreakable. Then came 1956.

Long story short, scientists have found something that violates the P part of CPT symmetry. It’s called the weak force and dictates things like neutrino collisions and element fusion in the sun. Everyone was shocked, confused, and scared.

Almost every fundamental concept of physics is based on CPT symmetry.

About a decade later, researchers discovered the weak force violating C-symmetry. Things fell apart. Physicists might hope and pray that even if P is violated… and CP is violated… maybe CPT still isn’t. Perhaps weak forces need the trio to maintain CPT symmetry. Fortunately, this theory seems correct. For some unknown reason, the weak point follows the overall CPT symmetry despite C and CP blips. Relief.

But here’s the problem. If weak forces violate CP symmetry, you would expect that t too. Well, they don’t, and physicists don’t know why. This is called the big CP proble, where it gets interesting.

Neutrons – uncharged particles in atoms – adhere to the strong force. Moreover, allowing for simplification, their neutral charge means they violate T-symmetry. And “if we find something that violates T symmetry, then it must also violate CP symmetry in such a way that the combination CPT is not violated,” the paper states. But… that’s weird—neutrons, not because of the big CP problem.

And so the idea of ​​the axion was born.

Neutrons are uncharged particles right in the center of atoms.


Years ago, physicists Roberto Peccei and Helen Quinn proposed adding a new dimension to the Standard Model. It involved a field of ultralight particles – axions – that explained the big CP problem, relaxing the conditions for neutrons. Axions seemed to solve everything so well that the duo’s idea became the “most popular solution to the strong CP problem,” the paper states. It was a miracle.

To be clear, axions are still hypothetical but think about what just happened. Physicists added a new particle to the Standard Model, which outlines dots of the entire Universe. What could that mean for everything else?

The key to dark matter?

According to the Peccei-Quinn theory, axions would be “cold” or move slowly through space. And… the study researchers say “the existence of” [dark matter] is inferred from its gravitational effects, and astrophysical observations suggest it is ‘cold’.”

The paper also states, “there are experimental upper limits for how strong… [the axion] interacts with visible matter.”

Sy, axions that help explain the big CP problem also seem to have theoretical properties similar to those of dark matter. Extremely good.

The European Council for Nuclear Research, better known as CERN, which runs the Large Hadron Collider and directs antimatter studies, also underlines that “one of the most evocative properties of axions is that they can be produced naturally in enormous numbers.” shortly after the Big Bang. This population of axions would still be present today and could make up the dark matter of the Universe.”

One area of ​​SLAC research is reconstructing the formation of the Universe. We are familiar with galaxies, but this simulation shows strands of dark matter crisscrossing the cosmos. Galaxies form at the brighter nodes where density is highest.

SLAC National Accelerator Laboratory

There you go. Axons are among the most popular topics in physics because they seem to explain so much. But again, those sought-after bits are still hypothetical.

Will we ever find axions?

It’s been 40 years since scientists started hunting axons.

Most of these searches “mainly exploit the interaction of the action field with the electromagnetic fields,” says the authors of recent Science Advances reviews.

For example, CERN developed the Axion Search Telescope, a machine built to find a hint of the particles produced in the sun’s core. Strong electric fields inside our star could interact with axions — if they’re there.

NASA’s solar-powered sounding rocket mission reveals a stunning image of super-hot magnetic wires in the sun’s atmosphere.

University of Central Lancashire

But the quest has had some pretty big challenges so far. First, “the particle mass is not theoretically predictable,” the authors write — that is, we have very little idea of ​​what an axion might look like. Scientists are still looking for it while assuming an enormously wide range of masses. Recently, however, researchers have provided evidence that the particle is likely between 40 and 180 micro electron volts. That is unimaginably small, about one billionth the mass of an electron.

“In addition,” the team writes, “the axion signal is expected to be very narrow … and extremely weak because of the very weak couplings to Standard Model particles and fields.” Essentially, even if tiny axions go out of their way to signal their existence to us, we could miss them. Their signals can be so weak that we barely notice.

Despite these hurdles, the search for axion continues. Most scientists claim they must be somewhere, but they seem too good to be true when fully explaining dark matter.

“Most experimental attempts assume that axions make up 100% of the dark matter halo,” the study authors point out, suggesting that there may be a way to “look at axion physics without relying on such an assumption.” .”

While they may be the star of the show, what if axions are just one chapter in dark matter history?

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