Emergent Solution to the Strong CP Problem

Area of Science:

• Theoretical Physics
• Cosmology
• Particle Physics

Background:

• The strong CP problem, a persistent puzzle in particle physics, concerns the unexplained absence of CP violation in the strong nuclear force.
• The axion is a hypothetical particle proposed to solve the strong CP problem, but its experimental detection remains elusive.
• Dark matter constitutes a significant portion of the universe's mass, yet its fundamental nature and interactions are largely unknown.

Purpose of the Study:

• To propose a novel theoretical framework where the strong CP problem is resolved as an emergent phenomenon.
• To explore the possibility of dark matter's properties and interactions providing a solution to the strong CP problem.
• To investigate the role of collective excitations in dark matter as analogous to axion degrees of freedom.

Main Methods:

• Construction of a theory linking dark matter's background properties to the strong CP problem solution.
• Modeling dark matter as a vector particle with low-energy interactions involving its spin density coupled to GG[over ˜].
• Analysis of multibody collective excitations in dark matter, akin to spin waves, acting as effective axions.

Main Results:

• The theory demonstrates that dark matter's spin density can induce a potential that compensates for CP violation (θ[over ¯]) in the strong sector.
• CP violation is effectively removed in regions with sufficient dark matter density.
• Viable parameter space suggests light dark matter masses, approaching the fuzzy dark matter limit, are preferred.

Conclusions:

• The study presents a compelling scenario where dark matter itself offers a natural solution to the strong CP problem.
• Collective excitations within dark matter can mimic axion behavior, providing a mechanism for CP symmetry.
• The proposed model predicts observable signals associated with light dark matter, warranting further investigation.