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A bstract Axions and axion-like particles (ALPs) are well-motivated low-energy relics of high-energy extensions of the Standard Model (SM). We investigate the phenomenology of an ALP with flavor-changing couplings, and present a comprehensive analysis of quark and lepton flavor-changing observables within a general ALP effective field theory. Observables studied include rare meson decays, flavor oscillations of neutral mesons, rare lepton decays, and dipole moments. We derive bounds on the general ALP couplings as a function of its mass, consistently taking into account the ALP lifetime and branching ratios. We further calculate quark flavor-changing effects that are unavoidably induced by running and matching between the new physics scale and the scale of the measurements. This allows us to derive bounds on benchmark ALP models in which only a single (flavorless or flavor-universal) ALP coupling to SM particles is present at the new physics scale, and in this context we highlight the complementarity and competitiveness of flavor bounds with constraints derived from collider, beam dump and astrophysical measurements. We find that searches for ALPs produced in meson decays provide some of the strongest constraints in the MeV-GeV mass range, even for the most flavorless of ALP models. Likewise, we discuss the interplay of flavor-conserving and flavor-violating couplings of the ALP to leptons, finding that constraints from lepton flavor-violating observables generally depend strongly on both. Additionally, we analyze whether an ALP can provide an explanation for various experimental anomalies including those observed in rare B -meson decays, measurements at the ATOMKI and KTeV experiments, and in the anomalous magnetic moments of the muon and the electron.

A bstract Motivated by the recent LHCb announcement of a 3 . 1 σ violation of lepton- flavor universality in the ratio R K = Γ( B → Kμ + μ − ) / Γ( B → Ke + e − ), we present an updated, comprehensive analysis of the flavor anomalies seen in both neutral-current ( b → sℓ + ℓ − ) and charged-current ( b → cτ ν ¯ ) decays of B mesons. Our study starts from a model-independent effective field-theory approach and then considers both a simplified model and a UV-complete extension of the Standard Model featuring a vector leptoquark U 1 as the main mediator of the anomalies. We show that the new LHCb data corroborate the emerging pattern of a new, predominantly left-handed, semileptonic current-current interaction with a flavor structure respecting a (minimally) broken U(2) 5 flavor symmetry. New aspects of our analysis include a combined analysis of the semileptonic operators involving tau leptons, including in particular the important constraint from B s - B ¯ s mixing, a systematic study of the effects of right-handed leptoquark couplings and of deviations from minimal flavor-symmetry breaking, a detailed analysis of various rare B -decay modes which would provide smoking-gun signatures of this non-standard framework (LFV decays, di-tau modes, and B → K (*) ν ν ¯ ), and finally an updated analysis of collider bounds on the leptoquark mass and couplings.

A bstract Motivated by additional experimental hints of Lepton Flavour Universality violation in B decays, both in charged- and in neutral-current processes, we analyse the ingredients necessary to provide a combined description of these phenomena. By means of an Effective Field Theory (EFT) approach, based on the hypothesis of New Physics coupled predominantly to the third generation of left-handed quarks and leptons, we show how this is possible. We demonstrate, in particular, how to solve the problems posed by electroweak precision tests and direct searches with a rather natural choice of model parameters, within the context of a U(2) q ×U(2) ℓ flavour symmetry. We further exemplify the general EFT findings by means of simplified models with explicit mediators in the TeV range: coloured scalar or vector leptoquarks and colour-less vectors. Among these, the case of an SU(2) L -singlet vector leptoquark emerges as a particularly simple and successful framework.

A bstract In recent years, experiments revealed intriguing hints for new physics (NP) in semi-leptonic B decays. Both in charged current processes, involving b → cτν transitions, and in the neutral currents b → sℓ + ℓ − , a preference for NP compared to the standard model (SM) of more that 3 σ and 5 σ was found, respectively. In addition, there is the long-standing tension between the theory prediction and the measurement of the anomalous magnetic moment (AMM) of the muon ( a μ ) of more than 3 σ . Since all these observables are related to the violation of lepton flavor universality (LFU), a common NP explanation seems not only plausible but is even desirable. In this context, leptoquarks (LQs) are especially promising since they give tree-level effects in semi-leptonic B decays, but only loop-suppressed effects in other flavor observables that agree well with their SM predictions. Furthermore, LQs can lead to a m t / m μ enhanced effect in a μ , allowing for an explanation even with (multi) TeV particles. However, a single scalar LQ representation cannot provide a common solution to all three anomalies. In this article we therefore consider a model in which we combine two scalar LQs: the SU(2) L singlet and the SU(2) L triplet. Within this model we compute all relevant 1-loop effects and perform a comprehensive phenomenological analysis, pointing out various interesting correlations among the observables. Furthermore, we identify benchmark points which are in fact able to explain all three anomalies ( b → cτν , b → sℓ + ℓ − and a μ ), without violating bounds from other observables, and study their predictions for future measurements.

A bstract We provide a comprehensive global analysis of Run II top measurements at the LHC in terms of dimension-6 operators. A distinctive feature of the top sector as compared to the Higgs-electroweak sector is the large number of four-quark operators. We discuss in detail how they can be tested and how quadratic terms lead to a stable limit on each individual Wilson coefficient. Predictions for all observables are computed at NLO in QCD. Our SF itter analysis framework features a detailed error treatment, including correlations between uncertainties.

A bstract Stringent relations between the B (∗) → D (∗) form factors exist in the heavy quark limit and the leading symmetry breaking corrections are known. We reconsider their uncertainty and role in the analysis of recent Belle data for B → D (∗) ℓ ν with model-independent parametrizations and in the related prediction of R ( D (∗) ). We find | V cb | = 41.5(1.3) 10 −3 and | V cb | = 40.6( − 1.3 + 1.2 ) 10 −3 using input from Light Cone Sum Rules, and R ( D ∗ ) = 0.260(8).

A bstract We extract | V cb | from the available data in the decay B → D (∗) ℓν ℓ . B → D ∗ ℓν ℓ , the unfolded binned differential decay rates of four kinematic variables including the q 2 bins have been used. In the CLN and BGL parameterizations of the form factors, the combined fit to all the available data along with their correlations yields | V cb | = (39.77 ± 0.89) × 10 −3 and (40.90 ± 0.94) × 10 −3 respectively. In these fits, we have used the inputs from lattice and light cone sum rule (LCSR) along with the data. Using our fit results and the HQET relations (with the known corrections included) amongst the form factors, and parameterizing the unknown higher order corrections (in the ratios of HQET form factors) with a conservative estimate of the normalizing parameters, we obtain R ( D ∗ ) = 0.259 ± 0.006 (CLN) and R ( D ∗ ) = 0.257 ± 0.005 (BGL).

A bstract Strengthening constraints on new physics from the B ¯ → X s γ branching ratio requires improving accuracy in the measurements and the Standard Model predictions. To match the expected Belle-II accuracy, Next-to-Next-to-Leading Order (NNLO) QCD corrections must be calculated without the so-far employed interpolation in the charm- quark mass m c . In the process of evaluating such corrections at the physical value of mc , we have finalized the part coming from diagrams with closed fermion loops on the gluon lines that contribute to the interference of the current-current and photonic dipole operators. We confirm several published results for corrections of this type, and supplement them with a previously uncalculated piece. Taking into account the recently improved estimates of non-perturbative contributions, we find ℬ sγ = (3 . 40 ± 0 . 17) × 10 − 4 and R γ ≡ ℬ s + d γ / ℬ c ℓ v ¯ = (3 . 35 ± 0 . 16) × 10 − 3 for E γ > 1 . 6 GeV in the decaying meson rest frame.

A bstract We provide a systematic treatment of the previously discovered power- enhanced QED corrections to the leptonic decay B q → μ + μ − ( q = d, s ) in the frame- work of soft-collinear effective theory (SCET). Employing two-step matching on SCETI and SCET II , and the respective renormalization group equations, we sum the leading- logarithmic QED corrections and the mixed QED-QCD corrections to all orders in the couplings for the matrix element of the semileptonic weak effective operator Q 9 . We pro- pose a treatment of the B -meson decay constant and light-cone distribution amplitude in the presence of process-specific QED corrections. Finally we include ultrasoft photon radiation and provide updated values of the non-radiative and radiative branching fractions of B q → μ + μ − decay that include the double-logarithmic QED and QCD corrections.

A bstract We perform a complete study of the low-energy phenomenology of S 1 and S 3 leptoquarks, aimed at addressing the observed deviations in B -meson decays and the muon magnetic dipole moment. Leptoquark contributions to observables are computed at one-loop accuracy in an effective field theory approach, using the recently published complete one-loop matching of these leptoquarks to the Standard Model effective field theory. We present several scenarios, discussing in each case the preferred parameter space and the most relevant observables.