Strong P invariance, neutron EDM and minimal Left-Right parity at LHC

TL;DR

This paper investigates constraints on Left-Right symmetric models from neutron EDM measurements, showing that parity symmetry imposes strong bounds, while charge conjugation symmetry remains less constrained, affecting the potential discovery reach at the LHC.

Contribution

It provides a detailed analysis of how different left-right symmetries impact neutron EDM constraints and explores possible mechanisms to relax these bounds.

Findings

Parity symmetry leads to strong constraints from neutron EDMs.

Charge conjugation symmetry is less constrained, allowing lower right-handed scale.

Updated calculations of neutron EDM contributions refine the bounds on $W_R$ mass.

Abstract

In the minimal Left-Right model the choice of left-right symmetry is twofold: either generalized parity $\mathcal P$ or charge conjugation $\mathcal C$. In the minimal model with spontaneously broken strict $\mathcal P$, a large tree-level contribution to strong CP violation can be computed in terms of the spontaneous phase $\alpha$. Searches for the neutron electric dipole moments then constrain the size of $\alpha$. Following the latest update on indirect CP violation in the kaon sector, a bound on $W_R$ mass at $20 \text{TeV}$ is set. Possible ways out of this bound, either by an additional relaxation mechanism or explicit breaking of $\mathcal P$ are considered. To this end, the chiral loop of the neutron electric dipole moment at next-to-leading order is re-computed and provides an estimate of the weak contribution. Combining this constraint with other CP violating observables in the kaon sector allows for $M_{W_R} \gtrsim 3 \text{TeV}$. On the other hand, $\mathcal C$-symmetry is free from such constraints, leaving the right-handed scale within the experimental reach.