Morisi, S., Nebot, M., Patel, K. M., Peinado, E., & Valle, J. W. F. (2013). Quark-lepton mass relation and CKM mixing in an A(4) extension of the minimal supersymmetric standard model. Phys. Rev. D, 88(3), 036001–8pp.
Abstract: An interesting mass relation between down-type quarks and charged leptons has been recently predicted within a supersymmetric SU(3)(c) circle times SU(2)(L) circle times U(1)(Y) model based on the A(4) flavor symmetry. Here we propose a simple extension which provides an adequate full description of the quark sector. By adding a pair of vectorlike up quarks, we show how the CKM entries V-ub, V-cb, V-td and V-ts arise from deviations of the unitarity. We perform an analysis including the most relevant observables in the quark sector, such as oscillations and rare decays of kaons, B-d and B-s mesons. In the lepton sector, the model predicts an inverted hierarchy for the neutrino masses, leading to a potentially observable rate of neutrinoless double beta decay.
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Botella, F. J., Branco, G. C., Nebot, M., & Sanchez, A. (2015). Mixing asymmetries in B meson systems, the D0 like-sign dimuon asymmetry, and generic new physics. Phys. Rev. D, 91(3), 035013–14pp.
Abstract: The measurement of a large like-sign dimuon asymmetry A(SL)(b) by the D0 experiment at the Tevatron departs noticeably from Standard Model (SM) expectations and it may be interpreted as a hint of physics beyond the Standard Model contributing to Delta B not equal 0 transitions. In this work we analyze how the natural suppression of A(SL)(b) in the SM can be circumvented by new physics. We consider generic Standard Model extensions where the charged current mixing matrix is enlarged with respect to the usual 3 x 3 unitary Cabibbo-Kobayashi-Maskawa matrix, and show how, within this framework, a significant enhancement over Standard Model expectations for Ab SL is easily reachable through enhancements of the semileptonic asymmetries A(SL)(d) and A(SL)(s) of both B-d(0)- (B) over bar (0)(d) and B-s(0)- (B) over bar (0)(s) systems. Despite being insufficient to reproduce the D0 measurement, such deviations from SM expectations may be probed by the LHCb experiment.
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Botella, F. J., Branco, G. C., Nebot, M., & Rebelo, M. N. (2016). Flavour-changing Higgs couplings in a class of two Higgs doublet models. Eur. Phys. J. C, 76(3), 161–17pp.
Abstract: We analyse various flavour-changing processes like t -> hu, hc, h -> t e, tau μas well as hadronic decays h -> bs, bd, in the framework of a class of two Higgs doublet models where there are flavour-changing neutral scalar currents at tree level. These models have the remarkable feature of having these flavour-violating couplings entirely determined by the CKM and PMNS matrices as well as tan beta. The flavour structure of these scalar currents results from a symmetry of the Lagrangian and therefore it is natural and stable under the renormalisation group. We show that in some of the models the rates of the above flavour-changing processes can reach the discovery level at the LHC at 13 TeV even taking into account the stringent bounds on low energy processes, in particular μ-> e gamma.
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Bonilla, C., Nebot, M., Valle, J. W. F., & Srivastava, R. (2016). Flavor physics scenario for the 750 GeV diphoton anomaly. Phys. Rev. D, 93(7), 073009–5pp.
Abstract: A simple variant of a realistic flavor symmetry scheme for fermion masses and mixings provides a possible interpretation of the diphoton anomaly as an electroweak singlet “flavon.” The existence of TeV scale vectorlike T-quarks required to provide adequate values for Cabibbo-Kobayashi-Maskawa (CKM) parameters can also naturally account for the diphoton anomaly. Correlations between V-ub and V-cb with the vectorlike T-quark mass can be predicted. Should the diphoton anomaly survive in a future run, our proposed interpretation can also be tested in upcoming B and LHC studies.
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Bernabeu, J., Botella, F. J., & Nebot, M. (2016). Genuine T, CP, CPT asymmetry parameters for the entangled B-d system. J. High Energy Phys., 06(6), 100–24pp.
Abstract: The precise connection between the theoretical T, CP, CPT asymmetries, in terms of transition probabilities between the filtered neutral meson B-d states, and the experimental asymmetries, in terms of the double decay rate intensities for Flavour-CP eigenstate decay products in a B-d-factory of entangled states, is established. This allows the identification of genuine Asymmetry Parameters in the time distribution of the asymmetries and their measurability by disentangling genuine and possible fake terms. We express the nine asymmetry parameters three different observables for each one of the three symmetries in terms of the ingredients of the Weisskopf-Wigner dynamical description of the entangled B-d-meson states and we obtain a global fit to their values from the BaBar collaboration experimental results. The possible fake terms are all compatible with zero and the information content of the nine asymmetry parameters is indeed different. The non -vanishing Delta l(c)(T) = 0.687 +/- 0.020 and Delta l(c)(CP) = 0.680 +/- 0.021 are impressive separate direct evidence of Time -Reversal -violation and CP-violation in these transitions and compatible with Standard Model expectations. An intriguing 2 sigma effect for the Re(theta) parameter responsible of CPT -violation appears which, interpreted as an upper limit, leads to vertical bar M (B) over baro (B) over baro vertical bar MBoBo < 4.0 x 10(-5) eV at 95% C.L. for the diagonal flavour terms of the mass matrix. It contributes to the CP-violating Delta l(c)(CP) asymmetry parameter in an unorthodox manner – in its cos(Delta M t) time dependence-, and it is accessible in facilities with non-entangled B-d's, like the LHCb experiment.
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