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- Abelian symmetries in the two-Higgs-doublet model with fermionsPublication . Ferreira, Pedro Miguel; Silva, João PauloWe classify all possible implementations of an Abelian symmetry in the two-Higgs-doublet model with fermions. We identify those symmetries which are consistent with nonvanishing quark masses and a Cabibbo-Kobayashi-Maskawa quark-mixing matrix (CKM), which is not block-diagonal. Our analysis takes us from a plethora of possibilities down to 246 relevant cases, requiring only 34 distinct matrix forms. We show that applying Z(n) with n >= 4 to the scalar sector leads to a continuous U(1) symmetry in the whole Lagrangian. Finally, we address the possibilities of spontaneous CP violation and of natural suppression of the flavor-changing neutral currents. We explain why our work is relevant even for non-Abelian symmetries.
- Flavour symmetries in a renormalizable SO(10) modelPublication . Ferreira, Pedro Miguel; Grimus, W.; Jurciukonis, D.; Lavoura, L.In the context of a renormalizable supersymmetric SO(10) Grand Unified Theory, we consider the fermion mass matrices generated by the Yukawa couplings to a 10 circle plus 120 circle plus (126) over bar representation of scalars. We perform a complete investigation of the possibilities of imposing flavour symmetries in this scenario; the purpose is to reduce the number of Yukawa coupling constants in order to identify potentially predictive models. We have found that there are only 14 inequivalent cases of Yukawa coupling matrices, out of which 13 cases are generated by 74 symmetries, with suitable n, and one case is generated by a Z(2) x Z(2) symmetry. A numerical analysis of the 14 cases reveals that only two of them-dubbed A and B in the present paper allow good fits to the experimentally known fermion masses and mixings. (C) 2016 The Authors. Published by Elsevier B.V.
- High scale impact in alignment and decoupling in two-Higgs-doublet modelsPublication . Basler, Philipp; Ferreira, Pedro Miguel; Muehlleitner, Milada Margarete; Santos, RuiThe two-Higgs-doublet model (2HDM) provides an excellent benchmark to study physics beyond the Standard Model (SM). In this work, we discuss how the behavior of the model at high-energy scales causes it to have a scalar with properties very similar to those of the SM-which means the 2HDM can be seen to naturally favor a decoupling or alignment limit. For a type II 2HDM, we show that requiring the model to be theoretically valid up to a scale of 1 TeV, by studying the renormalization group equations (RGE) of the parameters of the model, causes a significant reduction in the allowed magnitude of the quartic couplings. This, combined with B-physics bounds, forces the model to be naturally decoupled. As a consequence, any nondecoupling limits in type II, like the wrong-sign scenario, are excluded. On the contrary, even with the very constraining limits for the Higgs couplings from the LHC, the type I model can deviate substantially from alignment. An RGE analysis similar to that made for type II shows, however, that requiring a single scalar to be heavier than about 500 GeV would be sufficient for the model to be decoupled. Finally, we show that the 2HDM is stable up to the Planck scale independently of which of the CP-even scalars is the discovered 125 GeV Higgs boson.
- Are there hidden scalars in LHC Higgs results?Publication . Arhrib, A.; Ferreira, Pedro Miguel; Santos, RuiThe Higgs boson recently discovered at the Large Hadron Collider has shown to have couplings to the remaining particles well within what is predicted by the Standard Model. The search for other new heavy scalar states has so far revealed to be fruitless, imposing constraints on the existence of new scalar particles. However, it is still possible that any existing heavy scalars would preferentially decay to final states involving the light Higgs boson thus evading the current LHC bounds on heavy scalar states. Moreover, decays of the heavy scalars could increase the number of light Higgs bosons being produced. Since the number of light Higgs bosons decaying to Standard Model particles is within the predicted range, this could mean that part of the light Higgs bosons could have their origin in heavy scalar decays. This situation would occur if the light Higgs couplings to Standard Model particles were reduced by a concomitant amount. Using a very simple extension of the SM - the two-Higgs doublet model we show that in fact we could already be observing the effect of the heavy scalar states even if all results related to the Higgs are in excellent agreement with the Standard Model predictions.
- Preserving the validity of the two-Higgs-doublet model up to the Planck scalePublication . Ferreira, Pedro Miguel; Haber, Howard E.; Santos, EdwardWe examine the constraints on the two Higgs doublet model (2HDM) due to the stability of the scalar potential and absence of Landau poles at energy scales below the Planck scale. We employ the most general 2HDM that incorporates an approximately Standard Model (SM) Higgs boson with a flavor aligned Yukawa sector to eliminate potential tree-level Higgs-mediated flavor changing neutral currents. Using basis independent techniques, we exhibit robust regimes of the 2HDM parameter space with a 125 GeV SM-like Higgs boson that is stable and perturbative up to the Planck scale. Implications for the heavy scalar spectrum are exhibited.
- One-loop contributions to neutral minima in the inert doublet modelPublication . Ferreira, Pedro Miguel; Swiezewska, BogumilaThe vacuum structure of the inert doublet model is analysed at the one-loop level using the effective potential formalism, to verify the validity of tree-level predictions for the properties of the global minimum. An inert minimum (with massive fermions) and an inert-like minimum (with massless fermions) can coexist at tree level. But the one-loop analysis reveals that the allowed parameter space for the coexistence of more than one minimum is larger than the tree-level expected one. It is also shown that for some choices of parameters, the global minimum found at the one-loop level may be inert (or inert-like), contrary to what the tree-level analysis indicates.
- Electroweak vacuum lifetime in two Higgs doublet modelsPublication . Branchina, V.; Contino, F.; Ferreira, Pedro MiguelWe study the stability of neutral electroweak vacua in two Higgs doublet models, and calculate the lifetime of these states when the parameters are such that they are false vacua. As the two Higgs doublet model is invariant under a sign change of both doublets, degenerate true vacua exist. It is shown that this degeneracy, despite the fact that each of these minima locally describes the same physics, can immensely affect their lifetime. We apply these calculations to the parameter space of the models which is allowed by recent LHC searches, and infer combinations of parameters which should be excluded on grounds of a tunneling time inferior to the age of the universe.
- Probing wrong-sign Yukawa couplings at the LHC and a future linear colliderPublication . Ferreira, Pedro Miguel; Santos, Rui; Gunion, John F.; Haber, HowardWe consider the two-Higgs-doublet model as a framework in which to evaluate the viability of scenarios in which the sign of the coupling of the observed Higgs boson to down-type fermions (in particular, b-quark pairs) is opposite to that of the Standard Model (SM), while at the same time all other tree-level couplings are close to the SM values. We show that, whereas such a scenario is consistent with current LHC observations, both future running at the LHC and a future e(+)e(-) linear collider could determine the sign of the Higgs coupling to b-quark pairs. Discrimination is possible for two reasons. First, the interference between the b-quark and the t-quark loop contributions to the ggh coupling changes sign. Second, the charged-Higgs loop contribution to the gamma gamma h coupling is large and fairly constant up to the largest charged-Higgs mass allowed by tree-level unitarity bounds when the b-quark Yukawa coupling has the opposite sign from that of the SM (the change in sign of the interference terms between the b-quark loop and the W and t loops having negligible impact).
- Models with extended Higgs sectors at future e(+)e(-) collidersPublication . Azevedo, Duarte; Ferreira, Pedro Miguel; Muehlleitner, Milada Margarete; Santos, Rui; Wittbrodt, JonasWe discuss the phenomenology of several beyond the Standard Model (SM) extensions that include extended Higgs sectors. The models discussed are the SM extended by a complex singlet field, the 2-Higgs-doublet model with a CP-conserving and a CP-violating scalar sector, the singlet extension of the 2-Higgs-doublet model, and the next-to-minimal supersymmetric SM extension. All the above models have at least three neutral scalars, with one being the 125 GeV Higgs boson. This common feature allows us to compare the production and decay rates of the other two scalars and therefore to compare their behavior at future electron-positron colliders. Using predictions on the expected precision of the 125 GeV Higgs boson couplings at these colliders we are able to obtain the allowed admixtures of either a singlet or a pseudoscalar to the observed 125 GeV scalar. Therefore, even if no new scalar is found, the expected precision at future electron-positron colliders, such as CLIC, will certainly contribute to a clearer picture of the nature of the discovered Riggs boson.
- Scotogenic model for co-bimaximal mixingPublication . Ferreira, Pedro Miguel; Grimus, W.; Jurciukonis, D.; Lavoura, L.We present a scotogenic model, i.e. a one-loop neutrino mass model with dark right-handed neutrino gauge singlets and one inert dark scalar gauge doublet eta, which has symmetries that lead to co-bimaximal mixing, i.e. to an atmospheric mixing angle theta(23) = 45 degrees and to a CP-violating phase delta = +/-pi/2, while the mixing angle theta(13) remains arbitrary. The symmetries consist of softly broken lepton numbers L-alpha (alpha = e, mu, tau), a non-standard CP symmetry, and three L-2 symmetries. We indicate two possibilities for extending the model to the quark sector. Since the model has, besides eta, three scalar gauge doublets, we perform a thorough discussion of its scalar sector. We demonstrate that it can accommodate a Standard Model-like scalar with mass 125 GeV, with all the other charged and neutral scalars having much higher masses.