Flavor-diagonal CP violation: the electric dipole moment

Abstract

The observed baryon asymmetry in the universe cannot be reconciled with the current form of the Standard Model (SM) of particle physics. The Standard Model breaks charge conjugation parity (CP) symmetry, but not in a sufficient amount to explain the observed matter-antimatter asymmetry. Historically one of the first systems to be studied in the search of symmetry breaking within the Standard Model is the electric dipole moment (EDM) of the neutron. The contribution to the neutron EDM coming from the SM is several order of magnitudes smaller than the current experimental bound, thus providing a unique, background-free window for potential discovery of physics Beyond the Standard Model (BSM). The strong CP-violating term can also contribute to the neutron EDM, as can all the CP-violating effective operators describing, at energies below the electro-weak scale, the contributions from BSM. To constrain all these contributions to the neutron EDM we need to precisely determine the hadronic matrix elements of the corresponding renormalized operators. After a brief introduction on baryon asymmetry and baryogenesis, I summarize the current stuatus for experiments in search of a neutron EDM. I then describe in more details the different CP-violating sources, and some results in Chiral Perturbation Theory precede a discussion on the current status of Lattice QCD calculations. I will in particular focus on the 2 main challenges for these type of calculations: the signal-to-noise ratio and the renormalization. I will discuss several improvement techniques trying to improve these two aspects of the calculation and I will conclude with an optimistic view into the future.

Topical issue on Lattice Field Theory during the Covid-19 pandemic

“… Excited states in nucleon structure calculations (K. Ottnad) [ 5 ]. Flavor-diagonal CP violation: the electric dipole moment (A. Shindler) [ 6 ]. Past, present, and future of precision determinations of the QCD parameters from lattice QCD (M. Dalla Brida) [ 7 ].…”

Uncovering an Axion Mechanism with the EDM Portfolio

“…To make the most of existing and future experiments, hadronic and nuclear theory must be improved. Lattice QCD calculations are underway that connect dimension-six operators, such as the quark chromo-EDM, to nucleon EDMs [113,114] but still have a long way to go. Improved nuclear structure calculations of, for example, 199 Hg and 225 Ra EDMs would be very beneficial in connecting observed patterns of EDMs to ultraviolet physics and the nature of the solution to the strong CP problem.…”

Erratum to: Topical issue on Lattice Field Theory during the Covid-19 pandemic

“… Excited states in nucleon structure calculations (K. Ottnad) [ 5 ]. Flavor-diagonal CP violation: the electric dipole moment (A. Shindler) [ 6 ]. Past, present, and future of precision determinations of the QCD coupling from lattice QCD (M. Dalla Brida) [ 7 ].…”