The anatomy of Z′ and Z with flavour changing neutral currents in the flavour precision era

By Andrzej Buras, F. Fazio, J. Girrbach. 2012

165 citations recorded by the source corpus.

A bstractThe simplest extension of the Standard Model (SM) that generally introduces new sources of flavour violation and CP violation as well as right-handed (RH) currents is the addition of a U(1) gauge symmetry to the SM gauge group. If the corresponding heavy gauge boson (Z′) mediates FCNC processes in the quark sector at tree-level, these new physics (NP) contributions imply a pattern of deviations from SM expectations for FCNC processes that depends only on the couplings of Z′ to fermions and on its mass. This implies stringent correlations between ΔF = 2 and ΔF = 1 observables which govern the landscape of the allowed parameter space for Z′-models. Anticipating the Flavour Precision Era (FPE) ahead of us we illustrate this by searching for allowed oases in this landscape assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. To this end we analyze ΔF = 2 observables in $ {K^0}-{{\overline{K}}^0} $ and $ B_{s,d}^0-\overline{B}_{s,d}^0 $ systems and rare K and B decays including both left-handed and right-handed Z′-couplings to quarks in various combinations. We identify a number of correlations between various flavour observables that could test and distinguish these different Z′ scenarios. The important role of b → sℓ+ℓ− and $ b\to s\nu \overline{\nu} $ transitions in these studies is emphasized. Imposing the existing flavour constraints, a rich pattern of deviations from the SM expectations in Bs,d and K meson systems emerges provided MZ′ ≤ 3 TeV. While for MZ′ ≥ 5 TeV Z′ effects in rare Bs,d decays are found typically below 10% and hard to measure even in the FPE, $ K\to s\nu \overline{\nu} $ and KL → π0ℓ+ℓ− decays provide an important portal to scales beyond those explored by the LHC. We apply our formalism to NP scenarios with induced flavour changing neutral Z-couplings to quarks. We find that in the case of Bd and K decays such Z-couplings still allow for sizable departures from the SM. On the other hand in the Bs system, constraints on b → sℓ+ℓ− transitions basically eliminate NP effects from such couplings.

Subfields: Artificial Intelligence, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/38b3add0af6fed0f32edacf8c8ded6f7e5267607

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Citations in the corpus

Improved anatomy of ε′/ε in the Standard Model (2015, methodology): “In several models, like littlest Higgs model with T-parity (LHT) [47], and generally Z–models with new FCNCs, only in left-handed currents [20, 48], enhancement of the branching ratio for KL → πνν̄ is significantly constrained by ε′/ε because in these models such an enhancement is correlated with th”
Rare $B$ Decays as Tests of the Standard Model (2016, background): “[79]) or various types of scalar or vector leptoquarks [72].”
Electroweak constraints on flavorful effective theories (2015, background): “For the down sector, following [71], the strongest constrained are coming from ∆MK = (0.”
331 models facing new b → sμ+μ− data (2013, methodology): “(5)These coefficients are defined as in [19] and the same definitions are used in [10, 11].”
Patterns of flavour violation in models with vector-like quarks (2016, methodology): “[35], increasing the impact of |∆F | = 2 constraints on |∆F | = 1 processes relative to the one found in [35].”
New physics in B→K∗μμ? (2013, methodology): “To arrive at (13), we took the matching scale to be 1 TeV and used the hadronic matrix elements collected in [48].”