Converting invisible dark matter into visible light

Explorations into dark matter are advancing using new experimental techniques designed to detect axes, and leveraging advanced technology and interdisciplinary collaboration to uncover the secrets of this elusive component of the universe.

A ghost haunts our world. This has been known in astronomy and cosmology for decades. Notes I suggest it about 85% All matter in the universe is mysterious and invisible. These two qualities are reflected in its name: dark matter.

Several experiments They aim to uncover their ingredients, but despite decades of research, scientists have come up short. now Our new experienceunder construction in Yale University In the United States, it offers a new tactic.

Dark matter has been around the universe since the beginning of time. Pull stars and galaxies together. Invisible and subtle, it does not appear to interact with light or any other type of matter. In fact, it should be something completely new.

The Standard Model of particle physics is incomplete, and that's a problem. We have to look for the new Fundamental particles. Surprisingly, the same flaws of the standard model give precious hints about where they might be hiding.

The problem with the neutron

Take the neutron, for example. It forms the atomic nucleus with the proton. Although generally neutral, theory states that it is made up of three charged particles called quarks. For this reason, we expect some parts of the neutron to be positively charged and others negatively – meaning it had what physicists call an electric dipole moment.

Until now, Many attempts Measuring it led to the same conclusion: it is too small to be discovered. Another ghost. We are not talking about shortcomings in the instruments, but rather about a factor that must be smaller than one part in ten billion. It is so small that people wonder if it could be completely zero.

But in physics, mathematical zero is always a strong statement. In the late 1970s, particle physicists Roberto Picci and Helen Coyne (and later Frank Wilczek and Steven Weinberg) attempted to discover Understanding theory and evidence.

They suggested that the parameter is probably not zero. Rather, it is a dynamic quantity that slowly loses its charge, and then evolves to zero the great explosion. Theoretical calculations show that if such an event occurred, it must have left behind a large number of illusory light particles.

They are called “axions” after a brand of detergent because they can “solve” the neutron problem. And even more. If axions were created at the beginning of the universe, they have been around ever since. Most importantly, its properties define all the expected elements of dark matter. For these reasons, the hubs have become one of Preferred candidate particles For dark matter.

Axions will interact with other particles only weakly. However, this means that they will still interact quite a bit. Invisible axes can transform into ordinary particles, including – ironically – photons, the essence of light. This may happen under certain conditions, such as the presence of a magnetic field. This is a godsend for experimental physicists.

Experimental design

Many experiments They attempt to conjure the ghost of Axion in a controlled laboratory environment. Some of them aim to convert light into axis, for example, and then transform the axis into light on the other side of the wall.

At present, the most sensitive approach targets the dark matter halo that permeates the galaxy (and thus the Earth) using a device called a corona. It is a conductive cavity immersed in a strong magnetic field. The former picks up the dark matter surrounding us (assuming it's axons), while the latter prompts it to turn into light. The result is an electromagnetic signal that appears inside the cavity, oscillating at a characteristic frequency depending on the axion's mass.

The system works like a radio receiver. It must be properly adjusted to intercept the frequency of interest. In practice, the dimensions of the cavity are changed to accommodate different characteristic frequencies. If the axion and cavity frequencies do not match, it is like tuning the radio to the wrong channel.

The powerful magnet is transported to the laboratory at Yale University. Credit: Yale University

Unfortunately, the channel we are looking for cannot be predicted in advance. We have no choice but to scan all possible frequencies. It's like selecting a radio station in a sea of ​​white noise – a needle in a haystack – with an old radio that needs to be made larger or smaller every time we turn the frequency knob.

However, these are not the only challenges. Cosmology refers to Tens of gigahertz As the latest promising frontier of the search for axions. Since higher frequencies require smaller cavities, exploring that region would require cavities that are too small to capture a meaningful amount of signal.

New experiments try to find alternative paths. our Longitudinal plasmascope experiment (Alpha). It uses a new concept of cavitation based on metamaterials.

Metamaterials are composite materials with universal properties that differ from their components – they are more than the sum of their parts. A cavity filled with conducting rods gets a distinct frequency as if it were a million times smaller, while its size barely changes. This is exactly what we need. Additionally, the bars offer a built-in, easy-to-adjust adjustment system.

We are currently building the setup, which will be ready to receive data in a few years. The technology is promising. Its development was the result of collaboration between solid-state physicists, electrical engineers, particle physicists, and even mathematicians.

Although far-fetched, axions are fueling progress that no specter will ever be able to eliminate.

Written by Andrea Gallo Russo, Postdoctoral Fellow in Physics, Stockholm University.

Adapted from an article originally published in Conversation.