A Theoretical Breakthrough: Exploring Dark Matter and the Cosmic Web with Axions

In a study published today in Journal of Cosmology and AstrophysicsResearchers at the University of Toronto have revealed a theoretical breakthrough that could explain the invisible nature of dark matter and the large-scale structure of the universe known as the cosmic web. The results establish a new relationship between two longstanding problems in astronomy, opening up new possibilities for understanding the universe.

Research suggests that the “clumping problem”, which centers on the unexpectedly even distribution of matter on large scales throughout the universe, may be a sign that dark matter is composed of hypothetical ultralight particles called axions. The implications of proving the existence of such a hard-to-detect axis go far beyond understanding dark matter and could answer fundamental questions about the nature of the universe itself.

“If confirmed by telescope observations and future laboratory experiments, finding the dark matter axion will be one of the most important discoveries of this century,” said lead author Keir Rogers, a Dunlap researcher at the Dunlap Institute for Astronomy and Astrophysics in the College of Arts. and Astrophysics. Science at the University of Toronto.

“At the same time, our results suggest an explanation for why the universe is not as lumpy as we thought, an observation that has become clearer over the past decade, and is currently making our theory of the universe uncertain.”

Dark matter, which makes up 85% of the mass of the universe, is invisible because it doesn’t interact with light. Scientists study the effect of gravity on visible matter to understand how it is distributed in the universe.

One of the leading theories proposes that dark matter is made of axions, which are described in quantum mechanics as “fuzzy” because of their wave-like behavior. Unlike discrete point-like particles, axions can have longer wavelengths than entire galaxies. This ambiguity affects the composition and distribution of dark matter, which may explain why the universe is not as lumpy as would be expected in an axisless universe.

This lack of clumping has been observed in surveys of large galaxies, challenging the prevailing theory that dark matter is composed only of weakly interacting heavy subatomic particles called WIMPs. Apart from experiments such as the Large Hadron Collider, no evidence has been found to support the existence of WIMPs.

“In science, as ideas unravel, new discoveries are made and old problems are solved,” said Rogers.

For the study, the research team — led by Rogers, and including research group member Associate Professor Renee Hluczek at the Dunlap Institute, as well as from the University of Pennsylvania, Institute for Advanced Study, Columbia University and King’s College London — analyzed observations of the residual glow from the Big Bang, otherwise known as the Cosmic Microwave background (CMB), obtained from the 2018 Planck survey and the Atacama Cosmology and South Pole Telescope.

The researchers compared this CMB data with galaxy cluster data from the Baryon Oscillation Spectroscopic Survey (BOSS), which maps the locations of nearly a million galaxies in the nearby universe. By studying the distribution of galaxies, which reflects the behavior of dark matter under gravitational forces, they measured fluctuations in the amount of matter throughout the universe and confirmed its lower mass than predicted.

The researchers then ran computer simulations to predict the appearance of residual light and the distribution of galaxies in the universe with long wavelengths of dark matter. These calculations align with CMB data from the Big Bang and galaxy clustering data, supporting the idea that fuzzy axes can explain clustering problems.

Future research will include large-scale surveys to map millions of galaxies and provide accurate measurements of their clustering, including observations over the next decade with the Rubin Observatory.

The researchers hope to compare their theory to direct observations of dark matter via gravitational lensing, an effect in which dark matter agglomeration is measured by how light from distant galaxies is bent, similar to a giant magnifying glass. They also plan to investigate how galaxies emit gas into space and how this affects the distribution of dark matter to further confirm their findings.

Understanding the nature of dark matter is one of the most pressing fundamental questions and a key to understanding the origin and future of the universe.

Currently, scientists do not have a single theory that would explain gravity and quantum mechanics together – the theory of everything. The most popular theory of everything in recent decades is string theory, which posits another, lower quantum level, in which everything consists of string-like energy excitations. According to Rogers, the discovery of the mysterious axial particle could be a clue that string theory is all right.

“We now have a tool that, even in the next decade, could finally allow us to understand something empirically about a century-old mystery of dark matter — and that can give us clues to answers to bigger theoretical questions,” said Rogers. . “The hope is that the confusing elements of the universe can be solved.”