Eberhardt, O., Miralles, V., & Pich, A. (2021). Constraints on coloured scalars from global fits. J. High Energy Phys., 10(10), 123–23pp.
Abstract: We consider a simple extension of the electroweak theory, incorporating one SU(2)(L) doublet of colour-octet scalars with Yukawa couplings satisfying the principle of minimal flavour violation. Using the HEPfit package, we perform a global fit to the available data, including all relevant theoretical constraints, and extract the current bounds on the model parameters. Coloured scalars with masses below 1.05 TeV are already excluded, provided they are not fermiophobic. The mass splittings among the different (charged and CP-even and CP-odd neutral) scalars are restricted to be smaller than 20 GeV. Moreover, for scalar masses smaller than 1.5 TeV, the Yukawa coupling of the coloured scalar multiplet to the top quark cannot exceed the one of the SM Higgs doublet by more than 80%. These conclusions are quite generic and apply in more general frameworks (without fine tunings). The theoretical requirements of perturbative unitarity and vacuum stability enforce relevant constraints on the quartic scalar potential parameters that are not yet experimentally tested.
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Davier, M., Diaz-Calderon, D., Malaescu, B., Pich, A., Rodriguez-Sanchez, A., & Zhang, Z. (2023). The Euclidean Adler function and its interplay with Delta alpha(had)(QED) and alpha(s). J. High Energy Phys., 04(4), 067–57pp.
Abstract: Three different approaches to precisely describe the Adler function in the Euclidean regime at around 2 GeVs are available: dispersion relations based on the hadronic production data in e(+)e(-) annihilation, lattice simulations and perturbative QCD (pQCD). We make a comprehensive study of the perturbative approach, supplemented with the leading power corrections in the operator product expansion. All known contributions are included, with a careful assessment of uncertainties. The pQCD predictions are compared with the Adler functions extracted from ?a( QED)(had)(Q(2)), using both the DHMZ compilation of e(+)e(-) data and published lattice results. Taking as input the FLAG value of a(s), the pQCD Adler function turns out to be in good agreement with the lattice data, while the dispersive results lie systematically below them. Finally, we explore the sensitivity to a(s) of the direct comparison between the data-driven, lattice and QCD Euclidean Adler functions. The precision with which the renormalisation group equation can be tested is also evaluated.
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Cirigliano, V., Gisbert, H., Pich, A., & Rodriguez-Sanchez, A. (2020). Isospin-violating contributions to epsilon '/epsilon. J. High Energy Phys., 02(2), 032–44pp.
Abstract: The known isospin-breaking contributions to the K -> pi pi amplitudes are reanalyzed, taking into account our current understanding of the quark masses and the relevant non-perturbative inputs. We present a complete numerical reappraisal of the direct CP-violating ratio is an element of(')/is an element of, where these corrections play a quite significant role. We obtain the Standard Model prediction Re (is an element of(')/is an element of) = (14 +/- 5) <bold> </bold>10(-4), which is in very good agreement with the measured ratio. The uncertainty, which has been estimated conservatively, is dominated by our current ignorance about 1/N-C-suppressed contributions to some relevant chiral-perturbation-theory low-energy constants.
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Cirigliano, V., Ecker, G., Neufeld, H., Pich, A., & Portoles, J. (2012). Kaon decays in the standard model. Rev. Mod. Phys., 84(1), 399–447.
Abstract: A comprehensive overview of kaon decays is presented. The standard model predictions are discussed in detail, covering both the underlying short-distance electroweak dynamics and the important interplay of QCD at long distances. Chiral perturbation theory provides a universal framework for treating leptonic, semileptonic, and nonleptonic decays including rare and radiative modes. All allowed decay modes with branching ratios of at least 10 (11) are analyzed. Some decays with even smaller rates are also included. Decays that are strictly forbidden in the standard model are not considered in this review. The present experimental status and the prospects for future improvements are reviewed.
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Celis, A., Jung, M., Li, X. Q., & Pich, A. (2013). Sensitivity to charged scalars in B -> D-(*)tau nu(tau) and B -> tau nu(tau) decays. J. High Energy Phys., 01(1), 054–27pp.
Abstract: We analyze the recent experimental evidence for an excess of tau-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-(*)tau nu(tau) and the B -> tau nu(tau) 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 tau(-)(nu) over bar (tau) transitions.
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