Low-energy phenomenology of scalar leptoquarks at one-loop accuracy

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.

Section: Jhep03(2021)122supporting

confidence: 89%

Section: Flavour Spurions For Scalar Leptoquarksmentioning

confidence: 99%

Section: Jhep03(2021)122mentioning

confidence: 99%

Section: Jhep03(2021)122mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Constraining flavour patterns of scalar leptoquarks in the effective field theory

Bordone

Catà

Feldmann

et al. 2021

Scalar leptoquarks in leptonic processes

Crivellin

Greub

Müller

et al. 2021

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.

Leptoquark manoeuvres in the dark: a simultaneous solution of the dark matter problem and the $$ {R}_{D^{\left(\ast \right)}} $$ anomalies

Bélanger

Bharucha

Fuks

et al. 2022

The measured branching fractions of B-mesons into leptonic final states derived by the LHCb, Belle and BaBar collaborations hint towards the breakdown of lepton flavour universality. In this work we take at face value the so-called $$ {R}_{D^{\left(\ast \right)}} $$ R D ∗ observables that are defined as the ratios of neutral B-meson charged-current decays into a D(*)-meson, a charged lepton and a neutrino final state in the tau and light lepton channels. A well-studied and simple solution to this charged current anomaly is to introduce a scalar leptoquark S1 that couples to the second and third generation of fermions. We investigate how S1 can also serve as a mediator between the Standard Model and a dark sector. We study this scenario in detail and estimate the constraints arising from collider searches for leptoquarks, collider searches for missing energy signals, direct detection experiments and the dark matter relic abundance. We stress that the production of a pair of leptoquarks that decays into different final states (i.e. the commonly called “mixed” channels) provides critical information for identifying the underlying dynamics, and we exemplify this by studying the tτbν and the resonant S1 plus missing energy channels. We find that direct detection data provides non-negligible constraints on the leptoquark coupling to the dark sector, which in turn affects the relic abundance. We also show that the correct relic abundance can not only arise via standard freeze-out, but also through conversion-driven freeze-out. We illustrate the rich phenomenology of the model with a few selected benchmark points, providing a broad stroke of the interesting connection between lepton flavour universality violation and dark matter.