Axions

Definition

Axions are hypothetical, extremely lightweight particles that were first proposed to resolve an apparent conflict in the theory of quantum chromodynamics (QCD), the fundamental theory of strong interactions. These particles are of great interest in the context of cosmology and astrophysics, as they may provide insights into the nature of dark matter and the overall composition of the universe.

5 Must Know Facts For Your Next Test

1. Axions were originally proposed in 1977 as a solution to the so-called 'strong CP problem' in quantum chromodynamics (QCD), which relates to the observed lack of charge-parity (CP) violation in the strong interaction.
2. Axions are predicted to be extremely light, with a mass that is many orders of magnitude smaller than the masses of other known subatomic particles, such as electrons or protons.
3. Axions are theorized to be a type of weakly interacting, low-mass particle that could potentially make up a significant portion of the dark matter in the universe.
4. Experiments are currently underway to try to directly detect axions, which would provide important insights into the nature of dark matter and the overall composition of the universe.
5. The search for axions is a major focus of research in particle physics and cosmology, as their discovery could have profound implications for our understanding of the fundamental laws of nature.

Review Questions

• Explain how the concept of axions relates to the mass of the galaxy, as discussed in Topic 25.3.
  • Axions are hypothesized to be a component of dark matter, which makes up the majority of the mass of galaxies. If axions exist, they could account for a significant fraction of the unobserved, or 'missing', mass in galaxies that is inferred from the motion of visible matter and the gravitational effects it experiences. The detection of axions would therefore provide important clues about the overall mass distribution and composition of galaxies, as discussed in Topic 25.3.
• Describe how the properties of axions, as discussed in Topic 29.5, could inform our understanding of the overall composition of the universe.
  • Topic 29.5 explores the fundamental constituents of the universe, including the nature of dark matter. If axions are confirmed to exist and make up a portion of dark matter, it would provide valuable insights into the composition of the universe. Axions are predicted to be extremely lightweight particles that interact only weakly with normal matter, which could explain why dark matter has not been directly observed. The detection of axions would therefore be an important step in unraveling the mystery of what the universe is really made of, as discussed in Topic 29.5.
• Analyze how the potential discovery of axions could impact our understanding of the properties of galaxies, as outlined in Topic 26.3.
  • $$\text{If axions are confirmed to exist and make up a significant fraction of dark matter}, \text{it would have profound implications for our understanding of the properties of galaxies, as discussed in Topic 26.3.} \text{Dark matter is known to play a crucial role in the formation and evolution of galaxies,} \text{providing the gravitational scaffolding upon which galaxies are built.} \text{The detection of axions could shed light on the nature of this dark matter,} \text{potentially revealing new insights into the structure, dynamics, and overall properties of galaxies.}$$

Related terms

Dark Matter: The mysterious, invisible substance that makes up approximately 85% of the total matter in the universe, whose nature is not yet fully understood.

Quantum Chromodynamics (QCD): The fundamental theory that describes the strong interaction, one of the four fundamental forces in nature, which governs the behavior of quarks and gluons inside atomic nuclei.

Particle Physics: The branch of physics that studies the most fundamental constituents of matter and energy, and the interactions between them.