Flavor-diagonal CP violation: the electric dipole moment

Area of Science:

• Particle Physics
• Cosmology
• Quantum Chromodynamics

Background:

• The Standard Model (SM) of particle physics does not account for the observed baryon asymmetry in the universe.
• The SM's charge conjugation parity (CP) symmetry violation is insufficient to explain the matter-antimatter imbalance.
• The neutron electric dipole moment (EDM) is a sensitive probe for physics Beyond the Standard Model (BSM).

Purpose of the Study:

• To investigate the sources of CP violation beyond the Standard Model using the neutron EDM.
• To constrain contributions to the neutron EDM from BSM physics by calculating hadronic matrix elements.
• To review the current status of experimental searches for the neutron EDM and theoretical calculations.

Main Methods:

• Review of experimental efforts searching for the neutron EDM.
• Analysis of CP-violating sources, including the strong CP-violating $\theta$ term.
• Discussion of Chiral Perturbation Theory and Lattice Quantum Chromodynamics (QCD) calculations.
• Focus on challenges in Lattice QCD: signal-to-noise ratio and renormalization.
• Exploration of techniques to improve Lattice QCD calculations.

Main Results:

• The SM contribution to the neutron EDM is significantly smaller than current experimental limits.
• CP-violating operators from BSM physics can contribute to the neutron EDM.
• Lattice QCD calculations are crucial for constraining these BSM contributions.
• Key challenges in Lattice QCD include managing the signal-to-noise ratio and renormalization procedures.

Conclusions:

• The neutron EDM provides a promising, background-free avenue for discovering new physics.
• Precise determination of hadronic matrix elements is essential for interpreting neutron EDM experiments.
• Advancements in Lattice QCD, despite challenges, offer optimistic prospects for future discoveries.