Electric dipole moments of light nuclei from chiral effective field theory

Abstract

We set up the framework for the calculation of electric dipole moments (EDMs) of light nuclei using the systematic expansion provided by chiral effective field theory (EFT). We take into account parity (P ) and time-reversal (T ) violation which, at the quark-gluon level, originates from the QCD vacuum angle and dimension-six operators capturing physics beyond the Standard Model. We argue that EDMs of light nuclei can be expressed in terms of six low-energy constants that appear in the P -and T -violating nuclear potential and electric current. As examples, we calculate the EDMs of the deuteron, the triton, and 3 He in leading order in the EFT expansion.

Nuclear electric dipole moments in chiral effective field theory

“…The results for the phenomenological potentials considered are also shown in table 1 and agree (where a comparison is possible) with those in refs. [9][10][11][12][13][14][15][16][17]. The values from chiral and phenomenological potentials are in excellent agreement.…”

“…Other irreducible CP-conserving and CP-violating current operators only contribute toJ µ at N 2 LO as discussed in [15,16,18] and are thus irrelevant for this work. For 2N operators we use the definitions…”

“…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.…”

“…The various sources of CP violation at the energy scale Λ χ ∼ 1 GeV induce, in principle, an infinite set of CP-violating terms in the effective low-energy pion-nucleon Lagrangian that, however, can be ordered by a power-counting scheme [8,15,16,18,26]. It was concluded that the leading EDM contributions for nucleons and light nuclei can be expressed in terms of seven interactions:…”

“…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.…”