QCD axion from a higher dimensional gauge field theory

Area of Science:

• Particle Physics
• Cosmology
• String Theory

Background:

• The strong CP problem in Quantum Chromodynamics (QCD) requires a solution.
• Axions are hypothetical particles proposed to solve the strong CP problem.
• Existing axion models often face challenges with unwanted U(1)PQ breaking couplings.

Purpose of the Study:

• To propose a natural origin for a QCD axion within a five-dimensional (5D) orbifold field theory.
• To demonstrate how the axion coupling to the QCD anomaly can be derived from fundamental principles.
• To explain how unwanted axion couplings can be avoided and to predict a specific axion scale.

Main Methods:

• Utilizing a parity-odd gauge field in a 5D orbifold field theory.
• Deriving axion couplings from a 5D Chern-Simons coupling.
• Leveraging 5D gauge symmetry and locality to eliminate unwanted couplings.
• Incorporating a warped fifth dimension to suppress the axion scale.

Main Results:

• A natural mechanism for generating a QCD axion from a 5D gauge field is identified.
• The axion's coupling to the QCD anomaly is naturally explained via the Chern-Simons term.
• Unwanted U(1)PQ breaking axion couplings are successfully avoided.
• A warped extra dimension leads to a naturally suppressed intermediate axion scale (fa) between 10^10-10^12 GeV.

Conclusions:

• The proposed 5D orbifold field theory provides a compelling framework for a natural QCD axion.
• The model elegantly solves the strong CP problem while avoiding problematic axion couplings.
• The prediction of an intermediate axion scale is a significant outcome with potential observational consequences.