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We reemphasize the strong dependence of the branching ratios B(K + → π + ν ν) and B(K L → π 0 ν ν) on |V cb | that is stronger than in rare B decays, in particular for K L → π 0 ν ν. Thereby the persistent tension between inclusive and exclusive determinations of |V cb | weakens the power of these theoretically clean decays in the search for new physics (NP). We demonstrate how this uncertainty can be practically removed by considering within the SM suitable ratios of the two branching ratios between each other and with other observables like the branching ratios forWe use as basic CKM parameters V us , |V cb | and the angles β and γ in the unitarity triangle (UT) with the latter two determined through the measurements of tree-level B decays. This avoids the use of the problematic |V ub |. A ratio involving B(K + → π + ν ν) and B(B s → µ + µ − ) while being |V cb |-independent exhibits sizable dependence on the angle γ. It should be of interest for several experimental groups in the coming years. We point out that the |V cb |-independent ratio of B(B + → K + ν ν) and B(B s → µ + µ − ) from Belle II and LHCb signals a 1.8σ tension with its SM value. As a complementary test of the Standard Model we propose to extract |V cb | from different observables as a function of β and γ. We illustrate this with ε K , ∆M d and ∆M s finding tensions between these three determinations of |V cb | within the SM. We point out that from ∆M s and S ψK S alone one finds |V cb | = 41.7(6) × 10 −3 and |V ub | = 3.64(12) × 10 −3 . We stress the importance of a precise measurement of γ.

In this paper we present the complete one-loop matching conditions, up to dimension-six operators of the Standard Model effective field theory, resulting by integrating out the two scalar leptoquarks S 1 ∼ (3, 1) 1 3 and S 3 ∼ (3, 3) 1 3 . This allows a phenomenological study of low-energy constraints on this model at one-loop accuracy, which will be the focus of a subsequent work. Furthermore, it provides a rich comparison for functional and computational methods for one-loop matching, that are being developed. As a corollary result, we derive a complete set of dimension-six operators independent under integration by parts, but not under equations of motions, called Green's basis, as well as the complete reduction formulae from this set to the Warsaw basis.

We perform a complete study of the low-energy phenomenology of S1 and S3 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.

Finding better ways to prove the Standard Model Effective Field Theory is a very important direction of research. This paper focuses on measurements of Electroweak triple gauge couplings, paying special attention on the regime of validity of the Effective Field Theory (EFT). In this regard, one of our goals is to find measurements leading to a large increase of the interference between the SM amplitude and the contribution of irrelevant operators in the EFT. We propose two such distributions that will lead to a better accuracy. Improvements compared to the traditional methods as well as LHC high luminosity prospects are discussed.

We analyze a new class of FCNC processes, the f → f γ decays of a fermion f into a lighter (same-charge) fermion f plus a massless neutral vector boson, a dark photonγ. A massless dark photon does not interact at tree level with observable fields, and the f → f γ decay presents a characteristic signature where the final fermion f is balanced by a massless invisible system. Models recently proposed to explain the exponential spread in the standard-model Yukawa couplings can indeed foresee an extra unbroken dark U (1) gauge group, and the possibility to couple on-shell dark photons to standard-model fermions via one-loop magnetic-dipole kind of FCNC interactions. The latter are suppressed by the characteristic scale related to the mass of heavy messengers, connecting the standard model particles to the dark sector. We compute the corresponding decay rates for the top, bottom, and charm decays (t → cγ, uγ, b → sγ, dγ, and c → uγ), and for the charged-lepton decays (τ → µγ, eγ, and µ → eγ) in terms of model parameters. We find that large branching ratios for both quark and lepton decays are allowed in case the messenger masses are in the discovery range of the LHC. Implications of these new decay channels at present and future collider experiments are briefly discussed.arXiv:1607.05928v2 [hep-ph]

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The most common predictions for rare K and B decay branching ratios in the Standard Model in the literature are based on the CKM elements $$|V_{cb}|$$ | V cb | and $$|V_{ub}|$$ | V ub | resulting from global fits, that are in the ballpark of their inclusive and exclusive determinations, respectively. In the present paper we follow another route, which to our knowledge has not been explored for $$\Delta M_{s,d}$$ Δ M s , d and rare K and B decays by anybody to date. We assume, in contrast to the prevailing inclusive expectations for $$|V_{cb}|$$ | V cb | , that the future true values of $$|V_{cb}|$$ | V cb | and $$|V_{ub}|$$ | V ub | will be both from exclusive determinations; in practice we use the most recent averages from FLAG. With the precisely known $$|V_{us}|$$ | V us | the resulting rare decay branching ratios, $$\varepsilon _K$$ ε K , $$\Delta M_d$$ Δ M d , $$\Delta M_s$$ Δ M s and $$S_{\psi K_S}$$ S ψ K S depend then only on the angles $$\beta $$ β and $$\gamma $$ γ in the unitarity triangle that moreover are correlated through the CKM unitarity. An unusual pattern of SM predictions results from this study with some existing tensions being dwarfed and new tensions being born. In particular using HPQCD $$B^0_{s,d}-{{\bar{B}}}^0_{s,d}$$ B s , d 0 - B ¯ s , d 0 hadronic matrix elements a $$3.1\sigma $$ 3.1 σ tension in $$\Delta M_s$$ Δ M s independently of $$\gamma $$ γ is found. For $$60^\circ \le \gamma \le 75^\circ $$ 60 ∘ ≤ γ ≤ 75 ∘ the tension in $$\Delta M_d$$ Δ M d between $$4.0\sigma $$ 4.0 σ and $$1.1\sigma $$ 1.1 σ is found and in the case of $$\varepsilon _K$$ ε K between $$5.2\sigma $$ 5.2 σ and $$2.1\sigma $$ 2.1 σ . Moreover, the room for new physics in $$K^+\rightarrow \pi ^+\nu {\bar{\nu }}$$ K + → π + ν ν ¯ , $$K_L\rightarrow \pi ^0\nu {\bar{\nu }}$$ K L → π 0 ν ν ¯ and $$B\rightarrow K(K^*)\nu {\bar{\nu }}$$ B → K ( K ∗ ) ν ν ¯ decays is significantly increased. We compare the results in this EXCLUSIVE scenario with the HYBRID one in which $$|V_{cb}|$$ | V cb | in the former scenario is replaced by the most recent inclusive $$|V_{cb}|$$ | V cb | and present the dependence of all observables considered by us in both scenarios as functions of $$\gamma $$ γ . As a byproduct we compare the determination of $$|V_{cb}|$$ | V cb | from $$\Delta M_s$$ Δ M s , $$\Delta M_d$$ Δ M d , $$\varepsilon _K$$ ε K and $$S_{\psi K_S}$$ S ψ K S using $$B^0_{s,d}-{{\bar{B}}}^0_{s,d}$$ B s , d 0 - B ¯ s , d 0 hadronic matrix elements from LQCD with $$2+1+1$$ 2 + 1 + 1 flavours, $$2+1$$ 2 + 1 flavours and their average. Only for the $$2+1+1$$ 2 + 1 + 1 case values for $$\beta $$ β and $$\gamma $$ γ exist for which the same value of $$|V_{cb}|$$ | V cb | is found: $$|V_{cb}|=42.6(4)\times 10^{-3}$$ | V cb | = 42.6 ( 4 ) × 10 - 3 , $$\gamma =64.6(16)^\circ $$ γ = 64.6 ( 16 ) ∘ and $$\beta =22.2(7)^\circ $$ β = 22.2 ( 7 ) ∘ . This in turn implies a $$2.7\sigma $$ 2.7 σ anomaly in $$B_s\rightarrow \mu ^+\mu ^-$$ B s → μ + μ - .