Closing the window on single leptoquark solutions to the B-physics anomalies

133

126

Models of radiative Majorana neutrino masses require new scalars and/or fermions to induce lepton number violating interactions. We show that these new particles also generate observable neutrino nonstandard interactions (NSI) with matter. We classify radiative models as type-I or II, with type-I models containing at least one Standard Model (SM) particle inside the loop diagram generating neutrino mass, and type-II models having no SM particle inside the loop. While type-II radiative models do not generate NSI at tree-level, popular models which fall under the type-I category are shown, somewhat surprisingly, to generate observable NSI at tree-level, while being consistent with direct and indirect constraints from colliders, electroweak precision data and charged-lepton flavor violation (cLFV). We survey such models where neutrino masses arise at one, two and three loops. In the prototypical Zee model which generates neutrino masses via one-loop diagrams involving charged scalars, we find that diagonal NSI can be as large as (8%, 3.8%, 9.3%) for (ε ee , ε µµ , ε τ τ ), while off-diagonal NSI can be at most (1.5 × 10 −3 %, 0.56%, 0.34%) for (ε eµ , ε eτ , ε µτ ). In one-loop neutrino mass models using leptoquarks (LQs), (ε µµ , ε τ τ ) can be as large as (21.6%, 51.7%), while ε ee and (ε eµ , ε eτ , ε µτ ) can at most be 0.6%. Other twoand three-loop LQ models are found to give NSI of similar strength. The most stringent constraints on the diagonal NSI are found to come from neutrino oscillation and scattering experiments, while the off-diagonal NSI are mostly constrained by low-energy processes, such as atomic parity violation and cLFV. We also comment on the future sensitivity of these radiative models in long-baseline neutrino experiments, such as DUNE. While our analysis is focused on radiative neutrino mass models, it essentially covers all NSI possibilities with heavy mediators. arXiv:1907.09498v2 [hep-ph] 3 Oct 2019 Contents 7 Other type-I radiative models 76 7.1 One-loop models 77 7.1.1 Minimal radiative inverse seesaw model 77 7.1.2 One-loop model with vectorlike leptons 80 7.1.3 SU (2) L -singlet leptoquark model with vectorlike quark 82 7.1.4 SU (2) L -doublet leptoquark model with vectorlike quark 83 7.1.5 Model with SU (2) L -triplet leptoquark and vectorlike quark 84 7.1.6 A new extended one-loop leptoquark model 85 7.2 Two-loop models 87 7.2.1 Zee-Babu model 87 7.2.2 Leptoquark/diquark variant of the Zee-Babu model 88 7.2.3 Model with SU (2) L -doublet and singlet leptoquarks 89 7.2.4 Leptoquark model with SU (2) L -singlet vectorlike quark 90 7.2.5 Angelic model 91 7.2.6 Model with singlet scalar and vectorlike quark 92 7.2.7 Leptoquark model with vectorlike lepton 93 7.2.8 Leptoquark model with SU (2) L -doublet vectorlike quark 93 7.2.9 A new two-loop leptoquark model 94 7.3 Three-loop models 95 7.3.1 KNT Model 95 7.3.2 AKS model 96 7.3.3 Cocktail Model 97 7.3.4 Leptoquark variant of the KNT model 98 -ii -7.3.5 SU (2) L -singlet three-loop model 99 7.4 Four-and higher-loop models 100 8 Type II r...

Section: Nsi In One-loop Leptoquark Modelmentioning

confidence: 99%

Non-standard interactions in radiative neutrino mass models

Babu

Dev

Jana

et al. 2020

133

126

“…As leptoquarks, they appear together in models which tackle the flavour anomalies in the R K ( * ) and R D ( * ) observables [38][39][40][41][42]. S 1 coupling as a leptoquark is able to explain R D ( * ) (see, for example [43,44]) while S 3 coupling as a leptoquark is able explain R K ( * ) [45][46][47][48][49][50][51]. However, in order to generate neutrino mass in this model, the fermion content of the chosen effective operators forces us to have one of either S 1 or S 3 coupling as a leptoquark, and the other as a diquark.…”

Section: The Modelmentioning

confidence: 99%

Radiative neutrino mass model from a mass dimension-11 ∆L = 2 effective operator

Gargalionis

Popa-Mateiu

Volkas

2020

We present the first detailed phenomenological analysis of a radiative Majorana neutrino mass model constructed from opening up a ∆L = 2 mass-dimension-11 effective operator constructed out of standard model fields. While three such operators are generated, only one dominates neutrino mass generation, namely O 47 = L C LQ C QQQ C HH, where L denotes lepton doublet, Q quark doublet and H Higgs doublet. The underlying renormalisable theory contains the scalars S 1 ∼ (3, 1, 1/3) coupling as a diquark, S 3 ∼ (3, 3, 1/3) coupling as a leptoquark, and Φ 3 ∼ (3, 3, 2/3), which has no Yukawa couplings but does couple to S 1 and S 3 in addition to the gauge fields. Neutrino masses and mixings are generated at two-loop order. A feature of this model that is different from many other radiative models is the lack of proportionality to any quark and charged-lepton masses of the neutrino mass matrix. One consequence is that the scale of new physics can be as high as 10 7 TeV, despite the operator having a high mass dimension. This raises the prospect that ∆L = 2 effective operators at even higher mass dimensions may, when opened up, produce phenomenologically-viable radiative neutrino mass models. The parameter space of the model is explored through benchmark slices that are subject to experimental constraints from charged lepton flavour-violating decays, rare meson decays and neutral-meson mixing. The acceptable parameter space can accommodate the anomalies in R K ( * ) and the anomalous magnetic moment of the muon.

“…As an illustration of the method, we consider in detail the minimally extended MFV scenario that accounts for the present flavour anomalies. Since one of the most promising setups to fit the anomalies is a U 1 leptoquark model [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], one simply needs to consider the spurions which are associated with the fermion currents that the U 1 leptoquark is coupling to (see below). These spurions will be referred to as ∆ QL and ∆ DE in the following.…”

Section: Introductionmentioning

confidence: 99%

Effective theory approach to new physics with flavour: general framework and a leptoquark example

Bordone

Catà

Feldmann

2020

Extending the Standard Model with higher-dimensional operators in an effective-fieldtheory (EFT) approach provides a systematic framework to study new-physics (NP) effects from a bottom-up perspective, as long as the NP scale is sufficiently large compared to the energies probed in the experimental observables. However, when taking into account the different quark and lepton flavours, the number of free parameters increases dramatically, which makes generic studies of the NP flavour structure infeasible. In this paper, we address this issue in view of the recently observed "flavour anomalies" in B-meson decays, which we take as a motivation to develop a general framework that allows us to systematically reduce the number of flavour parameters in the EFT. This framework can be easily used in global fits to flavour observables at Belle II and LHCb as well as in analyses of flavour-dependent collider signatures at the LHC. Our formalism represents an extension of the well-known minimal-flavour-violation approach, and uses Froggatt-Nielsen charges to define the flavour power-counting. As a relevant illustration of the formalism, we apply it to the flavour structures which could be induced by a U 1 vector leptoquark, which represents one of the possible explanations for the recent hints of flavour non-universality in semileptonic B-decays. We study the phenomenological viability of this specific framework performing a fit to low-energy flavour observables.