2009/08/12 by Vincenzo Cirigliano, Martín González-Alonso, James Jenkins · 1 citation
Physics and Astronomy · #hep-ph
paper · pdf · doi:10.1016/j.nuclphysb.2009.12.020
23 pages, 1 table and 5 eps figures
arxiv created 2009/08/12 · arxiv updated 2015/05/13
We describe non-standard contributions to semileptonic processes in a model independent way in terms of an SU(2)L X U(1)Y invariant effective lagrangian at the weak scale, from which we derive the low-energy effective lagrangian governing muon and beta decays. We find that the deviation from Cabibbo universality, ΔCKM = |Vud|2 + |Vus|2 + |Vub|2 - 1, receives contributions from four effective operators. The phenomenological bound of ΔCKM = -1E-4 +- 6E-4 provides strong constraints on all four operators, corresponding to an effective scale greater than 11 TeV (90% CL). Depending on the operator, this constraint is at the same level or better then the Z pole observables. Conversely, precision electroweak constraints alone would allow universality violations as large as ΔCKM = -0.01 (90% CL). An observed nonzero ΔCKM at this level could be explained in terms of a single four-fermion operator which is relatively poorly constrained by electroweak precision measurements.