Unraveling models of CP violation through electric dipole moments of light nuclei

Abstract

We show that the proposed measurements of the electric dipole moments of light nuclei in storage rings would put strong constraints on models of flavor-diagonal CP violation. Our analysis is exemplified by a comparison of the Standard Model including the QCD theta term, the minimal left-right symmetric model, a specific version of the so-called aligned two-Higgs doublet model, and briefly the minimal supersymmetric extension of the Standard Model. By using effective field theory techniques we demonstrate to what extent measurements of the electric dipole moments of the nucleons, the deuteron, and helion could discriminate between these scenarios. We discuss how measurements of electric dipole moments of other systems relate to the light-nuclear measurements.

Nuclear electric dipole moments in chiral effective field theory

“…The concept of probing the QCD θ-term and BSM physics using EDMs of light nuclei has attracted much attention in recent years [8][9][10][11][12][13][14][15][16][17][18][19][20] and is the basic idea underlying plans for EDM measurements in dedicated storage rings [21][22][23][24][25]. The main advantage of light nuclei is that the associated nuclear physics is theoretically well under control, such that these systems can be used to probe the underlying CP-violating mechanism.…”

“…the θ-term and dimension-six sources) are expected to contribute to all CP-violating operators in eq. (1.1), but at different strengths based on the field content and chiral-symmetry properties of the source [10,15,16,18,19]. Different sources therefore yield different hierarchies of nucleon and nuclear EDM contributions which can explicitly be probed by EDM measurements.…”

“…or a CP-violating high-energy model (in ref. [19] the minimal left-right symmetric model (mLRSM) and the aligned two-Higgs doublet model were studied) has to be specified. The coefficients of eq.…”

“…In order to focus on the cases of the QCD θ-term and the mLRSM in the two subsequent sections, the discussion in ref. [19] is briefly repeated and updated.…”

“…We do not apply the value for δm str np used in refs. [16,18,19] here, but instead the more refined value δm str np = (2.44 ± 0.18) MeV, which follows from a weighted average of the values compiled in ref. [46] and the newest lattice result of ref.…”