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We perform a general model-independent analysis of b → cτν τ transitions, including measurements of R D , R D * , their q 2 differential distributions, the recently measured longitudinal D * polarization F D * L , and constraints from the B c → τν τ lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected b → cτν τ observables, such as the baryonic transition Λ b → Λ c τν τ , the ratio R J/ψ , the forward-backward asymmetries A D ( * ) FB , the τ polarization asymmetries P D ( * ) τ , and the longitudinal D * polarization fraction F D * L . The latter shows presently a slight tension with any new-physics model, such that an improved measurement could have an important impact. We also discuss the potential change due the very recently announced preliminary R D ( * ) measurement by the Belle collaboration.

The alignment in flavour space of the Yukawa matrices of a general two-Higgsdoublet model results in the absence of tree-level flavour-changing neutral currents. In addition to the usual fermion masses and mixings, the aligned Yukawa structure only contains three complex parameters ς f , which are potential new sources of CP violation [1]. For particular values of these three parameters all known specific implementations of the model based on discrete Z 2 symmetries are recovered. One of the most distinctive features of the two-Higgs-doublet model is the presence of a charged scalar H ± . In this work, we discuss its main phenomenological consequences in flavour-changing processes at low energies and derive the corresponding constraints on the parameters of the aligned two-Higgs-doublet model.

We analyze the recent experimental evidence for an excess of τ -lepton production in several exclusive semileptonic B-meson decays in the context of two-Higgs-doublet models. These decay modes are sensitive to the exchange of charged scalars and constrain strongly their Yukawa interactions. While the usual Type-II scenario cannot accommodate the recent BaBar data, this is possible within more general models in which the charged-scalar couplings to up-type quarks are not as suppressed. Both the B → D ( * ) τ ν τ and the B → τ ν τ data can be fitted within the framework of the Aligned Two-Higgs-Doublet Model, but the resulting parameter ranges are in conflict with the constraints from leptonic charm decays. This could indicate a departure from the family universality of the Yukawa couplings, beyond their characteristic fermion mass dependence. We discuss several new observables that are sensitive to a hypothetical charged-scalar contribution, demonstrating that they are well suited to distinguish between different scenarios of new physics in the scalar sector, and also between this group and models with different Dirac structures; their experimental study would therefore shed light on the relevance of scalar exchanges in semileptonic b → c τ −ν τ transitions.

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Electric dipole moments are extremely sensitive probes for additional sources of CP violation in new physics models. Specifically, they have been argued in the past to exclude new CP-violating phases in two-Higgs-doublet models. Since recently models including such phases have been discussed widely, we revisit the available constraints in the presence of mechanisms which are typically invoked to evade flavour-changing neutral currents. To that aim, we start by assessing the necessary calculations on the hadronic, nuclear and atomic/molecular level, deriving expressions with conservative error estimates. Their phenomenological analysis in the context of two-Higgs-doublet models yields strong constraints, in some cases weakened by a cancellation mechanism among contributions from neutral scalars. While the corresponding parameter combinations do not yet have to be unnaturally small, the constraints are likely to preclude large effects in other CPviolating observables. Nevertheless, the generically expected contributions to electric dipole moments in this class of models lie within the projected sensitivity of the next-generation experiments.

We study the patterns of flavour violation in renormalisable extensions of the Standard Model (SM) that contain vector-like quarks (VLQs) in a single complex representation of either the SM gauge group G SM or G SM ≡ G SM ⊗ U(1) Lµ−Lτ . We first decouple VLQs in the M = (1 − 10) TeV range and then at the electroweak scale also Z, Z gauge bosons and additional scalars to study the phenomenology. The results depend on the relative size of Z-and Z -induced flavour-changing neutral currents, as well as the size of |∆F | = 2 contributions including the effects of renormalisation group Yukawa evolution from M to the electroweak scale that turn out to be very important for models with right-handed currents through the generation of left-right operators. In addition to rare decays like P → ¯ , P → P ¯ , P → P νν with P = K, B s , B d and |∆F | = 2 observables we analyze the ratio ε /ε which appears in the SM to be significantly below the data. We study patterns and correlations between these observables which taken together should in the future allow for differentiating between VLQ models. In particular the patterns in models with left-handed and right-handed currents are markedly different from each other. Among the highlights are large Z-mediated new physics effects in Kaon observables in some of the models and significant effects in B s,d -observables. ε /ε can easily be made consistent with the data, implying then uniquely the suppression of K L → π 0 νν. Significant enhancements of Br(K + → π + νν) are still possible. We point out that the combination of NP effects to |∆F | = 2 and |∆F | = 1 observables in a given meson system generally allows to determine the masses of VLQs in a given representation independently of the size of VLQ couplings.

We perform a comprehensive analysis of scalar contributions in b → cτ ν transitions including the latest measurements of R(D ( * ) ), the q 2 differential distributions in B → D ( * ) τ ν, the τ polarization asymmetry for B → D * τ ν, and the bound derived from the total width of the Bc meson. We find that scalar contributions with the simultaneous presence of both left-and right-handed couplings to quarks can explain the available data, specifically R(D ( * ) ) together with the measured differential distributions. However, the constraints from the total Bc width present a slight tension with the current data on B → D * τ ν in this scenario, preferring smaller values for R(D * ). We discuss possibilities to disentangle scalar new physics from other new-physics scenarios like the presence of only a left-handed vector current, via additional observables in B → D ( * ) τ ν decays or additional decay modes like the baryonic Λ b → Λcτ ν and the inclusive B → Xcτ ν decays. We also analyze scalar contributions in b → uτ ν transitions, including the latest measurements of B → τ ν, providing predictions for Λ b → pτ ν and B → πτ ν decays. The potential complementarity between the b → u and b → c sectors is finally investigated once assumptions about the flavour structure of the underlying theory are made.