Anomalous solutions to the strong CP problem.

Area of Science:

• High Energy Physics
• Particle Physics
• Theoretical Physics

Background:

• The strong CP problem is a major unsolved puzzle in the Standard Model of particle physics.
• Existing solutions often require fine-tuning or introduce new, unobserved particles.
• Anomalous U(1) symmetries offer a potential framework for addressing this problem.

Purpose of the Study:

• To propose a new mechanism for solving the strong CP problem.
• To explore the implications of Z_{2} discrete and anomalous U(1) symmetries in this context.
• To present concrete, testable predictions for new physics.

Main Methods:

• Utilizing a Z_{2} discrete symmetry to equate theta angles of two gauge groups.
• Employing an anomalous U(1) symmetry to render the difference between theta angles physical.
• Developing two distinct models illustrating the infrared manifestation of the anomalous symmetry.

Main Results:

• The first model features massless bifundamental quarks, with the η^{'} boson relaxing the QCD theta angle to zero.
• The second model realizes the anomalous U(1) symmetry as a dynamically generated mass term that cancels the theta angle.
• Both models predict the existence of new colored particles at the TeV scale.

Conclusions:

• The proposed mechanism offers a compelling solution to the strong CP problem.
• The predicted TeV-scale colored particles provide a direct experimental signature for these models.
• This work opens new avenues for exploring solutions to fundamental problems in particle physics.