Search

Abstract We perform a detailed model-independent phenomenological analysis of B ¯ → D ¯ D $$ \overline{B}\to \overline{D}D $$ decays. Employing an SU(3) F analysis including symmetry-breaking contributions together with a conservative power counting for various suppression effects, we obtain updated Standard Model predictions for all branching fractions and CP asymmetries from a fit to the available experimental data, testable at Belle II and the LHC experiments. These results include all relevant suppressed contributions, thereby providing upper limits on subleading Standard Model (SM) effects like “penguin pollution”, enabling searches for physics beyond the SM. Importantly, allowing in the same fit for the production fractions of charged and neutral B mesons to be different, we find f d /f u = 0.86 ± 0.05, which is 2.5σ away from unity, which, if confirmed, would have important phenomenological consequences.

Abstract We perform a general model-independent analysis of b → cτ ν ¯ τ $$ b\to c\tau {\overline{\nu}}_{\tau } $$ transitions, including measurements of ℛ D , ℛ D∗, their q 2 differential distributions, the recently measured longitudinal D* polarization F L D ∗ $$ {F}_L^{D\ast } $$ , and constraints from the B c → τ ν ¯ τ $$ {B}_c\to \tau {\overline{\nu}}_{\tau } $$ 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 → cτ ν ¯ τ $$ b\to c\tau {\overline{\nu}}_{\tau } $$ observables, such as the baryonic transition Λ b → Λ c τ ν ¯ τ $$ {\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau } $$ , the ratio ℛ J/ψ , the forward-backward asymmetries A FB D ∗ $$ {\mathcal{A}}_{\mathrm{FB}}^{D\left(\ast \right)} $$ , the τ polarization asymmetries P τ D ∗ $$ {\mathcal{P}}_{\tau}^{D\left(\ast \right)} $$ , and the longitudinal D* polarization fraction F L D ∗ $$ {F}_L^{D\ast } $$ . 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 ∗ $$ {\mathrm{\mathcal{R}}}_{\mathcal{D}\left(\ast \right)} $$ measurement by the Belle collaboration.

Abstract B decays proceeding via b → cℓν transitions with ℓ = e or μ are tree-level processes in the Standard Model. They are used to measure the CKM element V cb , as such forming an important ingredient in the determination of e.g. the unitarity triangle; hence the question to which extent they can be affected by new physics contributions is important, specifically given the long-standing tension between V cb determinations from inclusive and exclusive decays and the significant hints for lepton flavour universality violation in b → cτ ν and b → sℓℓ decays. We perform a comprehensive model-independent analysis of new physics in b → cℓν, considering all combinations of scalar, vector and tensor interactions occuring in single-mediator scenarios. We include for the first time differential distributions of B → D ∗ ℓν angular observables for this purpose. We show that these are valuable in constraining non-standard interactions. Specifically, the zero-recoil endpoint of the B → Dℓν spectrum is extremely sensitive to scalar currents, while the maximum-recoil endpoint of the B → D ∗ ℓν spectrum with transversely polarized D ∗ is extremely sensitive to tensor currents. We also quantify the room for e-μ universality violation in b → cℓν transitions, predicted by some models suggested to solve the b → cτ ν anomalies, from a global fit to B → Dℓν and B → D ∗ ℓν for the first time. Specific new physics models, corresponding to all possible tree-level mediators, are also discussed. As a side effect, we present V cb determinations from exclusive B decays, both with frequentist and Bayesian statistics, leading to compatible results. The entire numerical analysis is based on open source code, allowing it to be easily adapted once new data or new form factors become available.

Abstract We perform model-independent analyses extracting limits for the electric dipole moment of the electron and the P,T-odd scalar-pseudoscalar (S-PS) nucleon-electron coupling from the most recent measurements with atoms and molecules. The analysis using paramagnetic systems, only, is improved substantially by the inclusion of the recent measurement on HfF+ ions, but complicated by the fact that the corresponding constraints are largely aligned, owing to a general relation between the coefficients for the two contributions. Since this same relation does not hold in diamagnetic systems, it is possible to find atoms that provide essentially orthogonal constraints to those from paramagnetic ones. However, the coefficients are suppressed in closed-shell systems and enhancements of P,T-odd effects are only prevalent in the presence of hyperfine interactions. We formulate the hyperfine-induced time-reversal-symmetry breaking S-PS nucleon-electron interaction in general atoms in a mixed perturbative and variational approach, based on electronic Dirac-wavefunctions including the effects of electron correlations. The method is applied to the Hg atom, yielding the first direct calculation of the coefficient of the S-PS nucleon-electron coupling in a diamagnetic system. This results in additionally improved model-independent limits for both the electron EDM and the nucleon-electron coupling from the global fit. Finally we employ this fit to provide indirect limits for several paramagnetic systems under investigation.

Abstract The renormalization group equations (RGEs) in Standard Model effective theory are usually either solved analytically, neglecting the scale dependence of gauge and Yukawa couplings, or numerically without such approximations. We present analytic solutions of RGEs that take into account the dominant scale dependence of the anomalous-dimension matrix due to the running of the QCD coupling α s and of the top-Yukawa coupling. We consider first the case for which a given operator is generated directly through mixing with the parent operator whose Wilson coefficient is non-vanishing at the new physics scale. Subsequently we consider the case of two-step running, in which two operators do not mix directly, but only via a third mediator operator. We generalize these solutions to an arbitrary number of operators and show how even in this case analytic solutions can be obtained.

Abstract We discuss Yukawa-enhanced contributions from Z-mediated new physics to down-type quark ΔF = 2 processes in the framework of the standard model gauge-invariant effective theory (SMEFT). Besides the renormalization group (RG) mixing of the Z-mediating ψ 2 H 2 D operators into ΔF = 2 operators, we include at the electroweak scale one-loop (NLO) matching corrections consistently, necessary for the removal of the matching scale dependence. We point out that the right-handed Z-mediated interactions generate through Yukawa RG mixing ΔF = 2 left-right operators, which are further enhanced through QCD RG effects and chirally enhanced hadronic matrix elements. We investigate the impact of these new effects on the known correlations between ΔF = 2 and ΔF = 1 transitions in the SMEFT framework and point out qualitative differences to previous parameterizations of Z-mediated new physics that arise for the left-handed case. We illustrate how specific models fit into our model-independent framework by using four models with vector-like quarks. We carry out model-independent analyses of scenarios with purely left-handed and purely right-handed new-physics Z couplings for each of the three sectors s → d, b → s and b → d. Specifically we discuss the correlations between ε′/ε, ε K , K L → μ + μ − K + → π + ν ν ¯ $$ {K}_L\to {\mu}^{+}{\mu}^{-}{K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ and K L → π 0 ν ν ¯ $$ {K}_L\to {\pi}^0\nu \overline{\nu} $$ in the Kaon sector, and ϕ s , B s → μ + μ − and B → K (*)(μ + μ − , ν ν ¯ $$ \nu \overline{\nu} $$ ) in the b → s sector and B d → μ + μ − in the b → d sector.

Abstract 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 GSM or G SM ′ ≡ GSM ⊗ U(1)L μ − L τ . 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 |ΔF | = 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 → ℓ ℓ ¯ , P → P ′ ℓ ℓ ¯ , P → P ′ ν ν ¯ $$ P\to \ell \overline{\ell},P\to {P}^{\prime}\ell \overline{\ell},P\to {P}^{\prime}\nu \overline{\nu} $$ with P = K, B s , B d and |ΔF | = 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 ν ν ¯ $$ {K}_L\to {\pi}^0\nu\ \overline{\nu} $$ . Significant enhancements of B r K + → π + ν ν ¯ $$ Br\left({K}^{+}\to {\pi}^{+}\nu \overline{\nu}\right) $$ are still possible. We point out that the combination of NP effects to |ΔF | = 2 and |ΔF | = 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.