Dark matter got its name because its components do not interact with ordinary matter in any way. However, scientists still hope that it consists of particles called axions and can manifest themselves in certain types of interaction.
Invisible Dark Matter
Observations show that about 85% of all matter in the universe is invisible and mysterious. They received the name “dark matter” from scientists, although in fact there is no confidence that these are not several different things combined under a common name.
The aim of several experiments is to find out what dark matter is made of, but despite decades of research, astronomers have not been successful. A new experiment by scientists from Yale University may finally provide an opportunity to see these mysterious particles.
Dark matter has existed in the universe since the beginning of time, it causes stars and galaxies to stick together. Invisible and subtle, it doesn’t seem to interact with light or any other kind of matter. In fact, it should be something completely new.
Axions
The key to understanding dark matter may be a well-known particle like the neutron. All attempts to find out if it is really neutral have ended with one result: if it exists, it is too small to be detected. And we are not talking about instrumental flaws, but about a parameter that should be less than one part per 10 billion. From a practical point of view, it can be considered zero one way or another.
In physics, however, mathematical zero is always a strong statement. In the late 70s, particle physicists Roberto Peccei and Helen Quinn (and later Frank Wilczek and Steven Weinberg) tried to reconcile theory and evidence.
They suggested that perhaps the neutron charge was not always zero. Most likely, this is a dynamic quantity that gradually tended to the modern value after the Big Bang. Theoretical calculations show that if such an event occurred, it should have left behind a lot of light and elusive particles.
They were named axions after a brand of detergent because they could “clean up” a neutron problem. And even more. If axions were created in the early universe, then they must still exist somewhere.
Most importantly, their properties meet all expectations regarding dark matter. For these reasons, axions have become one of the most beloved candidate particles for the role of its constituents, but it has not become especially easier, because they still interact with ordinary matter too weakly for easy detection.
How to detect dark matter particles
Many experiments attempt to induce axions in a controlled laboratory environment. Some of them are aimed, for example, at converting light into axions, and then axions back into light.
Now the best approach is aimed at the halo of dark matter permeating the galaxy (and, accordingly, the Earth), using an instrument called a haloscope. It is a capsule with a conductive cavity, immersed in a strong magnetic field. If dark matter really consists of axions, then in this way it can be forced to turn into ordinary matter. As a result, an electromagnetic signal appears inside the cavity, which oscillates with a characteristic frequency depending on the mass of axions.
The system works like a radio receiver. It needs to be set up correctly to intercept the frequency that interests us. In practice, the dimensions of the cavity change to accommodate different characteristic frequencies.
However, there are significant problems along the way. Cosmology indicates that it is best to search for axions at frequencies in the tens of gigahertz. This means that the capsule for such experiments must be tiny, so much so that it is difficult to manufacture.
New experiment will help to detect particles
New experiments try to find alternative ways. Axion Longitudinal Plasma Haloscope (Alpha) uses a new capsule concept based on metamaterials.
Metamaterials are composite materials with global properties that differ from their constituents, they are something more than the sum of their parts. The cavity filled with conductive rods receives a characteristic frequency, as if it has become a million times smaller, while almost not changing its volume. This is exactly what we need. In addition, the rods provide a built-in, easily adjustable tuning system.
Now scientists are building an installation that will be ready to receive data in a few years. The technology is promising, its development is the result of cooperation between solid state physicists, electrical engineers, particle physicists and even mathematicians.
According to phys.org
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