Kaon CP violation and neutron EDM in the minimal left-right symmetric model

Abstract

Within the minimal Left-Right (LR) symmetric model we revisit the predictions for the kaon CP violating observables ε and ε in correlation with the neutron electric dipole moment. We perform a complete study of the cross constraints on the model parameters, phases and the MW R scale, considering the two cases of extended parity or charge conjugation as LR discrete symmetries, together with the possible presence of a Peccei-Quinn symmetry. We discuss in particular two scenarios: whether the Standard Model saturates the experimental value of ε /ε or whether new physics is needed, still an open issue after the recent lattice results on the QCD penguin matrix elements. Within the first scenario, we find no constraints on the LR scale in the charge-conjugation case while in the parity case we show that MW R can be as low as 13 TeV. On the other side, the request that new physics contributes dominantly to ε implies strong correlations among the model parameters, with an upper bound of MW R < 8-100 TeV depending on tan β in the case of charge conjugation and a range of MW R 7-45 TeV in the parity setup. Both scenarios may be probed directly at future colliders and only indirectly at the LHC. * stefano.bertolini@sissa.it † Alessio.Maiezza@irb.hr ‡ fabrizio.nesti@aquila.infn.it Right (LR) symmetric theories, based on the gauge groupA particular role is played by the minimal version of the Left-Right symmetric models (LRSM) [9]. Besides being predictive, the model provides a natural rationale for the origin and smallness of the neutrino mass [10,11], a setup for the restoration of parity at high scale [12], and a novel source for neutrinoless double-beta decay [13,14]. The LRSM has aroused a renewed interest in the era of LHC, because of the possibility of a direct detection via the Keung-Senjanovic (KS) process [15], which violates lepton number in full analogy with the low energy neutrinoless double-beta decay.

Constraining the gauge and scalar sectors of the doublet left-right symmetric model

“…[45] TLRM with an additional discrete symmetry. Together with the requirement of model perturbativity [53] and constraints on CP violation [32], the W scale is pushed to at least 7 TeV. This value is somewhat larger than the ones quoted before and is similar to what is generally found in other models.…”

“…Studies in the framework of flavour physics suggest also that the structure for the right-handed "CKMlike" matrix should be quite different from the left-handed one [22][23][24][25][26]. A particularly important indirect constraint comes from kaon-meson mixing, pushing again the mass scale for the new scalar particles up to a few TeV or beyond [27][28][29][30][31][32], for which we reassessed short-distance QCD corrections in order to reach the accuracy now requested for such processes [33].…”

Pati-Salam axion

“…The difference between the two choices mainly regards the structure of CP violation (see e.g. [59][60][61]). 2 Since the key results of this work concerning Pati-Salam breaking dynamics will not be affected by this choice, we will stick for definiteness to the case of P.…”

Parity and the origin of neutrino mass

“…The knowledge of V q R leads furthermore to precise predictions for low energy processes, see e.g. [24].…”

“…The number of possible non-diagonal symmetric blocks and their combination will grow and can easily be calculated for each particular dimension. The general formulas (40) and (44) are valid in any dimension, and the task is greatly simplified by conditions (24), which tell us that s i are either real or come in complex conjugate pairs.…”