Abstract
The latest measurements of rare b → s decays in the LHCb experiment have led to results in tension with the predictions of the standard model (SM), including a tentative indication of the violation of lepton flavor universality. Assuming that this situation will persist because of new physics, we explore some of the potential consequences in the context of the SM extended with the seesaw mechanism involving right-handed neutrinos plus effective dimension-six lepton-quark operators under the framework of minimal flavor violation. We focus on a couple of such operators which can accommodate the LHCb anomalies and conform to the minimal flavor violation hypothesis in both their lepton and quark parts. We examine specifically the lepton-flavor-violating decays B → K(∗)ℓℓ′, B s → ϕℓℓ′, B → (π, ρ)ℓℓ′, and B d,s → ℓℓ′, as well as K L → eμ and K → πeμ, induced by such operators. The estimated branching fractions of some of these decay modes with μτ in the final states are allowed by the pertinent experimental constraints to reach a few times 10−7 if other operators do not yield competitive effects. We also look at the implications for B → K(∗)νν and K → πνν, finding that their rates can be a few times larger than their SM values. These results are testable in future experiments.
Highlights
JHEP08(2015)123 dimension-six lepton-quark operators with tensor structures are excluded by the measurements andscalar operators can explain them only with much fine-tuning [14], while the counterpart of LSM+NP with right-handed quark chirality leads to much poorer fits to the data [15, 16]
Assuming that this situation will persist because of new physics, we explore some of the potential consequences in the context of the standard model (SM) extended with the seesaw mechanism involving right-handed neutrinos plus effective dimension-six lepton-quark operators under the framework of minimal flavor violation
Adopting the effective theory framework of minimal flavor violation (MFV) based on the SM plus 3 heavy right-handed neutrinos participating in the seesaw mechanism, we concentrate on a couple of dimension-six 4-fermion operators which accommodate the interactions that can yield one of the best fits to the b → s data
Summary
In the SM supplemented with three right-handed Majorana neutrinos, the renormalizable Lagrangian for fermion masses can be written as. El,R represent right-handed up- and down-type quarks (neutrinos and charged leptons), respectively, H stands for the Higgs doublet, H = iτ2H∗ with τ2 being the second Pauli matrix, Mν is a matrix for the Majorana masses of νl,R, and νkc,R ≡ (νk,R)c, the superscript referring to charge conjuga√tion. Where the objects ∆qj and ∆lj are, respectively, of the same form as ∆q and ∆l in eq (2.9), but have their own independent coefficients ζrj and ξrj, and a = 1, 2, 3 is implicitly summed over These generalize operators that were previously introduced under the assumption of MFV only in the quark [38] or lepton [40] part.
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