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Celis, A., Fuentes-Martin, J., & Serodio, H. (2014). A class of invisible axion models with FCNCs at tree level. J. High Energy Phys., 12(12), 167–53pp.
Abstract: We build a class of invisible axion models with tree-level Flavor Changing Neutral Currents completely controlled by the fermion mixing matrices. The scalar sector of these models contains three-Higgs doublets and a complex scalar gauge singlet, with the same fermionic content as in the Standard Model. A horizontal Peccei-Quinn symmetry provides a solution to the strong CP problem and predicts the existence of a very light and weakly coupled pseudo-Goldstone boson, the invisible axion or familon. A phenomenological analysis is performed taking into account familon searches in rare kaon and muon decays, astrophysical considerations and axion searches via axion-photon conversion. Drastic differences are found in the axion properties of different models due to the strong hierarchy of the CKM matrix, making some of the models considered much more constrained than others. We also obtain that a rich variety of these models avoid the domain wall problem. A possible mechanism to protect the solution to the strong CP problem against gravitational effects is also discussed.
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Boucenna, S. M., Celis, A., Fuentes-Martin, J., Vicente, A., & Virto, J. (2016). Phenomenology of an SU(2) x SU(2) x U(1) model with lepton-flavour non-universality. J. High Energy Phys., 12(12), 059–43pp.
Abstract: We investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in b -> clv and b -> sl(+) l(-) decays at BaBar, Belle and LHCb. The model consists of an extended gauge group SU(2)(1) x SU(2)(2) x U(l)(Y) which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector -like fermions give rise to potentially large new physics contributions in flavour transitions mediated by WI and Z' bosons. This model can ease tensions in B -physics data while satisfying stringent bounds from flavour physics, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the ratios RM =Gamma(B -> M mu(+)mu(-))/Gamma(B -> Me(+)e(-)), with M = K*, phi, are found to be reduced with respect to the Standard Model expectation R-M similar or equal to 1.
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Celis, A., Fuentes-Martin, J., Vicente, A., & Virto, J. (2017). Gauge-invariant implications of the LHCb measurements on lepton-flavor nonuniversality. Phys. Rev. D, 96(3), 035026–8pp.
Abstract: We study the implications of the recent measurements of R-K and R-K* by the LHCb Collaboration. We do that by adopting a model-independent approach based on the Standard Model effective field theory (SMEFT), with the dominant new physics (NP) effects encoded in the coefficients of dimension-6 operators respecting the full Standard Model (SM) gauge symmetry. After providing simplified expressions for R-K and R-K*, we determine the implications of the recent LHCb results for these observables on the coefficients of the SMEFT operators at low and high energies. We also take into account all b -> sll data, which combined lead to effective NP scenarios with SM pulls in excess of 5 sigma. Thus, the operators discussed in this paper would be the first dimension-6 terms in the SM Lagrangian to be detected experimentally. Indirect constraints on these operators are also discussed. The results of this paper transcend the singularity of the present situation and set a standard for future analyses in b -> s transitions when the NP is assumed to lie above the electroweak scale.
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Abbas, G., Celis, A., Li, X. Q., Lu, J., & Pich, A. (2015). Flavour-changing top decays in the aligned two-Higgs-doublet model. J. High Energy Phys., 06(6), 005–26pp.
Abstract: We perform a complete one-loop computation of the two-body flavour-changing top decays t --> ch and t --> cV (V = gamma, Z), within the aligned two-Higgs-doublet model. We evaluate the impact of the model parameters on the associated branching ratios, taking into account constraints from flavour data and measurements of the Higgs properties. Assuming that the 125 GeV Higgs corresponds to the lightest CP-even scalar of the CP-conserving aligned two-Higgs-doublet model, we find that the rates for such flavour-changing top decays lie below the expected sensitivity of the future high-luminosity phase of the LHC. Measurements of the Higgs signal strength in the di-photon channel are found to play an important role in limiting the size of the t --> ch decay rate when the charged scalar of the model is light.
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Celis, A., Fuentes-Martin, J., Vicente, A., & Virto, J. (2017). DsixTools: the standard model effective field theory toolkit. Eur. Phys. J. C, 77(6), 405–40pp.
Abstract: We present DsixTools, a Mathematica package for the handling of the dimension-six standard model effective field theory. Among other features, DsixTools allows the user to perform the full one-loop renormalization group evolution of the Wilson coefficients in the Warsaw basis. This is achieved thanks to the SMEFTrunner module, which implements the full one-loop anomalous dimension matrix previously derived in the literature. In addition, DsixTools also contains modules devoted to the matching to the Delta B = Delta S = 1, 2 and Delta B = Delta C = 1 operators of the Weak Effective Theory at the electroweak scale, and their QCD and QED Renormalization group evolution below the electroweak scale.
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