scholarly journals Scalar leptoquarks in leptonic processes

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Andreas Crivellin ◽  
Christoph Greub ◽  
Dario Müller ◽  
Francesco Saturnino

Abstract Leptoquarks are hypothetical new particles, which couple quarks directly to leptons. They experienced a renaissance in recent years as they are prime candidates to explain the so-called flavor anomalies, i.e. the deviations between the Standard Model predictions and measurements in b → sℓ+ℓ− and b → cτν processes and in the anomalous magnetic moment of the muon. At the one-loop level these particles unavoidably generate effects in the purely leptonic processes like Z → ℓ+ℓ−, Z →$$ v\overline{v} $$ v v ¯ , W → ℓν and h → ℓ+ℓ− and can even generate non-zero rates for lepton flavor violating processes such as ℓ → ℓ′γ, Z → ℓ+ℓ′−, h → ℓ+ℓ′− and ℓ → 3ℓ′. In this article we calculate these processes for all five representations of scalar Leptoquarks. We include their most general interaction terms with the Standard Model Higgs boson, which leads to Leptoquark mixing after the former acquires a vacuum expectation value. In our phenomenological analysis we investigate the effects in modified lepton couplings to electroweak gauge bosons, we study the correlations of the anomalous magnetic moment of the muon with h → μ+μ− and Z → μ+μ− as well as the interplay between different lepton flavor violating decays.

2020 ◽  
Vol 2020 (3) ◽  
Author(s):  
Junichi Haruna ◽  
Hikaru Kawai

Abstract In the standard model, the weak scale is the only parameter with mass dimensions. This means that the standard model itself cannot explain the origin of the weak scale. On the other hand, from the results of recent accelerator experiments, except for some small corrections, the standard model has increased the possibility of being an effective theory up to the Planck scale. From these facts, it is naturally inferred that the weak scale is determined by some dynamics from the Planck scale. In order to answer this question, we rely on the multiple point criticality principle as a clue and consider the classically conformal $\mathbb{Z}_2\times \mathbb{Z}_2$ invariant two-scalar model as a minimal model in which the weak scale is generated dynamically from the Planck scale. This model contains only two real scalar fields and does not contain any fermions or gauge fields. In this model, due to a Coleman–Weinberg-like mechanism, the one-scalar field spontaneously breaks the $ \mathbb{Z}_2$ symmetry with a vacuum expectation value connected with the cutoff momentum. We investigate this using the one-loop effective potential, renormalization group and large-$N$ limit. We also investigate whether it is possible to reproduce the mass term and vacuum expectation value of the Higgs field by coupling this model with the standard model in the Higgs portal framework. In this case, the one-scalar field that does not break $\mathbb{Z}_2$ can be a candidate for dark matter and have a mass of about several TeV in appropriate parameters. On the other hand, the other scalar field breaks $\mathbb{Z}_2$ and has a mass of several tens of GeV. These results will be verifiable in near-future experiments.


2003 ◽  
Vol 18 (16) ◽  
pp. 2769-2778
Author(s):  
Graham D. Kribs

I explain the theoretical connection between lepton flavor violation and muon g - 2 in supersymmetry1. Given any central value deviation of muon g - 2 from the standard model that is assumed to be due to weak scale supersymmetry, I show that stringent bounds on lepton flavor violating scalar masses can be extracted. These bounds are essentially independent of supersymmetric parameter space. I then briefly compare this indirect handle on supersymmetric lepton flavor violation with direct observation at a future lepton collider operating in the e- e- mode. This is a summary of a talk given at e- e-01: 4th International Workshop on Electron-Electron Interactions at TeV Energies.


1992 ◽  
Vol 07 (04) ◽  
pp. 279-292 ◽  
Author(s):  
HEINZ KÖNIG

We present a detailed calculation of the contribution ∆aμ to the anomalous magnetic moment of the muon, when charginos and neutralinos are taken into account inside the relevant penguin diagrams. We consider the minimal supersymmetric standard model and include spontaneous R-parity breaking through the vacuum expectation value ντ of the scalar tau neutrino [Formula: see text]. We show that R-parity breaking leads to a result for Δaμ, which is less than a factor 10 below the experimental value.


2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Marzia Bordone ◽  
Oscar Catà ◽  
Thorsten Feldmann ◽  
Rusa Mandal

Abstract We investigate the viability of extending the Standard Model with S1 and S3 scalar leptoquarks when the flavour structure is parametrized in terms of Froggatt-Nielsen charges. In contrast to a similar analysis with a vector leptoquark, we find essentially two solutions for the charges that fit the experimental constraints, which are dominated by the current tensions in B decays. These two scenarios differ in their estimate of the anomalous magnetic moment of the muon, (g − 2), but they both predict sizeable contributions to τ → μγ, $$ {\overline{B}}_s $$ B ¯ s → τ±μ∓ and B+→ K+τ+μ− decays, whose branching ratios are close to the current experimental limits.


2018 ◽  
Vol 179 ◽  
pp. 01015 ◽  
Author(s):  
Dario Müller

While the LHC has not directly observed any new particle so far, experimental results from LHCb, BELLE and BABAR point towards the violation of lepton flavour universality in b ⟶ sℓ+ and b ⟶ c-ℓν. In this context, also the discrepancy in the anomalous magnetic moment of the muon can be interpreted as a sign of lepton flavour universality violation. Here we discuss how these hints for new physics can also be explained by introducing leptoquarks as an extension of the Standard Model. Indeed, leptoquarks are good candidates to explain the anomaly in the anomalous magnetic moment of the muon because of an mg/mμ enhanced contribution giving correlated effects in Z boson decays which is particularly interesting in the light of future precision experiments.


2020 ◽  
Vol 887 ◽  
pp. 1-166 ◽  
Author(s):  
T. Aoyama ◽  
N. Asmussen ◽  
M. Benayoun ◽  
J. Bijnens ◽  
T. Blum ◽  
...  

2018 ◽  
Vol 179 ◽  
pp. 01004 ◽  
Author(s):  
Tim Gorringe

The Fermilab muon g-2 experiment will measure the muon anomalous magnetic moment aμ to 140 ppb – a four-fold improvement over the earlier Brookhaven experiment. The measurement of aμ is well known as a unique test of the standard model with broad sensitivity to new interactions, particles and phenomena. The goal of 140 ppb is commensurate with ongoing improvements in the SM prediction of the anomalous moment and addresses the longstanding 3.5σ discrepancy between the BNL result and the SM prediction. In this article I discuss the physics motivation and experimental technique for measuring aμ, and the current status and the future work for the project.


2018 ◽  
Vol 179 ◽  
pp. 01008 ◽  
Author(s):  
Marc Knecht

Progress made on the theoretical aspects of the standard model contributions to the anomalous magnetic moment of the charged leptons since the first FCCP Workshop on Capri in 2015 is reviewed. Emphasis is in particular given to the various cross-checks that have already become available, or might become available in the future, for several important contributions.


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