A leptoquark model to accommodate RKexp<RKSMR_K^\mathrm{exp} <R_K^\mathrm{SM} and RK∗exp<RK∗SMR_{K^\ast}^\mathrm{exp}< R_{K^\ast}^\mathrm{SM}

We show that a modification of the model with a low energy scalar leptoquark state carrying hypercharge $Y=7/6$ allows to accommodate both $R_K<1$ and $R_{K^\ast}<1$, through loop effects, consistent with recent observations made at LHCb. We describe details of the model, compute the relevant Wilson coefficient and, after discussing a number of constraints, we examine the phenomenological consequences of the model. The bounds on the lepton flavor violating decay rates, induced by this model, include $\mathcal{B}(Z\to\mu\tau) \lesssim \mathcal{O}(10^{-7})$, and $\mathcal{B}(B\to K\mu\tau) \lesssim \mathcal{O}(10^{-9})$. We also comment on the interpretation of the bounds on the leptoquark mass obtained from the direct searches at LHC.Comment: 18 pages, 7 figures (published version

Seeking the CP-odd Higgs via h→ηc,bℓ+ℓ−h\rightarrow \eta_{c,b}\ell^+\ell^-

We show that the decay rates of the Higgs boson to a pseudoscalar quarkonium and a pair of leptons, $h\to P\ell^+\ell^-$ ($P\in\{\eta_c,\eta_b\}$), can be substantially enhanced in a scenario with two Higgs doublets with a softly broken $\mathbb{Z}_2$ symmetry (2HDM) when the CP-odd Higgs A is light, i.e. $m_A\lesssim m_h$. Depending on the type of 2HDM the enhancement of $\mathcal{B}(h\to \eta_{c,b}\tau^+\tau^-)$ with respect to its Standard Model value can be an order of magnitude larger, i.e. $\mathcal{O}(10^{-6}\div10^{-5})$. The decays $h\to P\ell^+\ell^-$ could therefore provide an efficient channel to investigate the presence of a light CP-odd Higgs $A$ and help to disentangle among various 2HDM scenarios.Comment: 19 pages, 6 figure

Complementarity of the constraints on New Physics from B_s -> mu+ mu- and from B -> K l+l- decays

We discuss the advantages of combining the experimental bound on Br(B_s -> mu+ mu-) and the measured Br(B -> K l+l-) to get the model independent constraints on physics beyond the Standard Model. Since the two decays give complementary information, one can study not only the absolute values of the Wilson coefficients that are zero in the Standard Model, but also their phases. To identify the sector in which the new physics might appear, information about the shapes of the transverse asymmetries in B -> K* l+l- at low q^2's can be particularly useful. We also emphasize the importance of measuring the forward-backward asymmetry in B -> K l+l- decay at large q^2's.Comment: 28 pp, 12 figures, 2 tables; v3: version as publishe

Two Higgs doublet models and b→ s exclusive decays

We computed the leading order Wilson coefficients relevant to all the exclusive b→sℓ+ℓ− decays in the framework of the two Higgs doublet model (2HDM) with a softly broken Z2 symmetry by including the O(mb) corrections. We elucidate the issue of appropriate matching between the full and the effective theory when dealing with the (pseudo-)scalar operators for which keeping the external momenta different from zero is necessary. We then make a phenomenological analysis by using the measured B(Bs→μ+μ−) and B(B→Kμ+μ−)high−q2 , for which the hadronic uncertainties are well controlled, and we discuss their impact on various types of 2HDM. A brief discussion of the decays with τ -leptons in the final state is provided too

Bˉ→Dτνˉτ\bar B\to D\tau\bar \nu_\tau vs. Bˉ→Dμνˉμ\bar B\to D\mu\bar \nu_\mu

Recent experimental results for the ratio of the branching fractions of $\bar B\to D^{(*)}\tau\bar \nu_\tau$ and $\bar B\to D^{(*)}\mu\bar \nu_\mu$ decays came as a surprise and lead to a discussion of possibility to constraining New Physics through these modes. Here we focus on ${\cal B}(\bar B\to D\tau\bar \nu_\tau)/{\cal B}(\bar B\to D\mu\bar \nu_\mu)$ and argue that the result is consistent with the Standard Model within $2\sigma$, and that the test of compatibility of this ratio with the Standard Model can be done experimentally with a minimal theory input. We also show that these two decay channels can provide us with quite good constraints of the New Physics couplings.Comment: 10 pages (published version

Impact of B→K0∗ℓ+ℓ−B\to K^\ast_0 \ell^+\ell^- on the New Physics search in B→K∗ℓ+ℓ−B\to K^\ast \ell^+\ell^- decay

We discuss the uncertainty related to the amount of unwanted $B\to K_0^\ast (K\pi)\ell^+\ell^-$ events in the sample of $B\to K^\ast (K\pi)\ell^+\ell^-$. Those events can increase the measured differential decay rate by up to 10% in the low $q^2$ region, and can be a source of non-negligible uncertainty in the full angular distribution of the $B\to K^\ast (K\pi)\ell^+\ell^-$ decay. Although the transverse asymmetries should be unaffected by the presence of the $S$-wave $K\pi$ pairs, coming from the scalar $K_0^\ast$ meson, we show that in practice their normalization might be sensitive to those events and could entail a sizable uncertainty in transverse asymmetries around $q^2=2 GeV^2$. For other $q^2$'s that error is under about 10%.Comment: 16 pages [as published in NPB