The Neutron and the Electron Electric Dipole Moment in N=1 Supergravity Unification

TL;DR

This work analyzes neutron and electron EDMs within minimal N=1 supergravity unification, incorporating two CP-violating phases and full one-loop contributions from gluino, chargino, and neutralino exchanges, as well as chromoelectric and Weinberg gluonic operators. By mapping the six-dimensional parameter space under radiative electroweak breaking and experimental EDM bounds, the authors demonstrate robust internal cancellations between gluino and chargino contributions, and among electric, chromoelectric, and gluonic terms, which can suppress the neutron EDM well below the electron EDM in certain regions. These cancellations alleviate the usual fine-tuning concerns for SUSY phases and allow natural-range superpartner spectra to remain consistent with current EDM constraints. The findings have implications for SUSY discovery at the LHC and motivate consideration of non-universal soft-breaking scenarios where similar cancellation mechanisms could operate.

Abstract

An analysis of the neutron EDM and of the electron EDM in minimal N=1 supergravity unification with two CP violating phases is given. For the neutron the analysis includes the complete one loop gluino, chargino, and neutralino exchange diagrams for the electric dipole and the chromoelectric dipole operators, and also the contribution of the purely gluonic dimension six operator. It is shown that there exist significant regions in the six dimensional parameter space of the model where cancellations between the gluino and the chargino exchanges reduce the electric and the chromoelectric contributions, and further cancellations among the electric, the chromoelectric, and the purely gluonic parts lead to a dramatic lowering of the neutron EDM sometimes below the electron EDM value. This phenomenon gives a new mechanism, i.e., that of internal cancellations, for the suppression of the neutron EDM in supersymmetric theories. The cancellation mechanism can significantly reduce the severe fine tuning problem associated with CP violating phases in SUSY and SUGRA unified models.