Quark flavour mixing with right-handed currents: an effective theory approach

The impact of right-handed currents in both charged- and neutral-current flavour-violating processes is analysed by means of an effective theory approach. More explicitly, we analyse the structure of dimension-six operators assuming a left-right symmetric flavour group, commuting with an underlying $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ global symmetry, broken only by two Yukawa couplings. The model contains a new unitary matrix controlling flavour-mixing in the right-handed sector. We determine the structure of this matrix by charged-current data, where the tension between inclusive and exclusive determinations of $|V_{ub}|$ can be solved. Having determined the size and the flavour structure of right-handed currents, we investigate how they would manifest themselves in neutral current processes, including particle-antiparticle mixing, $Z\to b \bar b$, $B_{s,d}\to \mu^+\mu^-$, $B\to {Xs,K,K*} \nu\bar\nu$, and $K\to \pi\nu\bar\nu$ decays. The possibility to explain a non-standard CP-violating phase in $B_s$ mixing in this context, and the comparison with other predictive new-physics frameworks addressing the same problem, is also discussed. While a large $S_{\psi \phi}$ asymmetry can easily be accommodated, we point out a tension in this framework between $|V_{ub}|$ and $S_{\psi K}$.