Percorrer por autor "Sher, Marc"
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- Could the LHC two-proton signal correspond to the heavier scalar in two-higgs-doublet models?Publication . Ferreira, P. M.; Santos, Rui; Sher, Marc; Silva, João P.LHC has reported tantalizing hints for a Higgs boson of mass 125 GeV decaying into two photons. We focus on two-Higgs-doublet Models, and study the interesting possibility that the heavier scalar H has been seen, with the lightest scalar h having thus far escaped detection. Nonobservation of h at LEP severely constrains the parameter-space of two-Higgs-doublet models. We analyze cases where the decay H -> hh is kinematically allowed, and cases where it is not, in the context of type I, type II, lepton-specific, and flipped models.
- g − 2Þμ in the 2HDM and slightly beyond: an updated viewPublication . Ferreira, Pedro Miguel; Gonçalves, B. L.; Joaquim, F. R.; Sher, MarcThe recent measurement of the muon g - 2 anomaly continues to defy a Standard Model explanation but can be accommodated within the framework of two-Higgs doublet models, although the pseudoscalar mass must be fairly light. If one further includes extra fermion content in the form of a generation of vectorlike leptons, the allowed parameter range that explains the anomaly is even further extended, and clashes with B-decay constraints may be avoided. We show how the muon magnetic moment anomaly can be fit within these models, under the assumption that the vectorlike leptons do not mix with the muon. We update previous analyses and include all theoretical and experimental constraints, including searches for extra scalars. It is shown that the inclusion of vectorlike fermions allows the lepton-specific and muon-specific models to perform much better in fitting the muon's g - 2. However, these fits do require the Yukawa coupling between the Higgs and the vectorlike leptons to be large, causing potential problems with perturbativity and unitarity, and thus, models in which the vectorlike leptons mix with the muon may be preferred.
- Implications of the LHC two-photon signal for two-Higgs-doublet modelsPublication . Ferreira, P. M.; Santos, Rui; Sher, Marc; Silva, João P.We study the implications for two-Higgs-doublet models of the recent announcement at the LHC giving a tantalizing hint for a Higgs boson of mass 125 GeV decaying into two photons. We require that the experimental result be within a factor of 2 of the theoretical standard model prediction, and analyze the type I and type II models as well as the lepton-specific and flipped models, subject to this requirement. It is assumed that there is no new physics other than two Higgs doublets. In all of the models, we display the allowed region of parameter space taking the recent LHC announcement at face value, and we analyze the W+W-, ZZ, (b) over barb, and tau(+)tau(-) expectations in these allowed regions. Throughout the entire range of parameter space allowed by the gamma gamma constraint, the numbers of events for Higgs decays into WW, ZZ, and b (b) over bar are not changed from the standard model by more than a factor of 2. In contrast, in the lepton-specific model, decays to tau(+)tau(-) are very sensitive across the entire gamma gamma-allowed region.
- Suppression of the Higgs boson dimuon decayPublication . Ferreira, Pedro Miguel; Sher, MarcIt is often stated that elimination of tree-level flavor-changing neutral currents in multi-Higgs models requires that all fermions of a given charge to couple to the same Higgs boson. A counterexample was provided by Abe, Sato, and Yagyu in a muon-specific two-Higgs doublet model. In this model, all fermions except the muon couple to one Higgs and the muon couples to the other. We study the phenomenology of the model and show that there is a wide range of parameter space in which the branching ratios of the 125 GeV Higgs are very close to their Standard Model values, with the exception of the branching ratio into muons, which can be substantially suppressed-this is an interesting possibility, since the current value of this branching ratio is 0.5 +/- 0.7 times the Standard Model value. We also study the charged Higgs boson and show that, if it is lighter than 200 GeV, it could have a large branching ratio into mu nu-even substantially larger than the usual decay into tau nu. The decays of the heavy neutral scalars are also studied. The model does have a relationship between the branching ratios of the 125 GeV Higgs into Z's, tau's, and mu's, which can be tested in future accelerators.
- Theory and phenomenology of two-higgs-doublet modelsPublication . Ferreira, P. M.; Branco, G. C.; Lavoura, L.; Rebelo, M. N.; Sher, Marc; Silva, João P.We discuss theoretical and phenomenological aspects of two-Higgs-doublet extensions of the Standard Model. In general, these extensions have scalar mediated flavour changing neutral currents which are strongly constrained by experiment. Various strategies are discussed to control these flavour changing scalar currents and their phenomenological consequences are analysed. In particular, scenarios with natural flavour conservation are investigated, including the so-called type I and type II models as well as lepton-specific and inert models. Type III models are then discussed, where scalar flavour changing neutral currents are present at tree level, but are suppressed by either a specific ansatz for the Yukawa couplings or by the introduction of family symmetries leading to a natural suppression mechanism. We also consider the phenomenology of charged scalars in these models. Next we turn to the role of symmetries in the scalar sector. We discuss the six symmetry-constrained scalar potentials and their extension into the fermion sector. The vacuum structure of the scalar potential is analysed, including a study of the vacuum stability conditions on the potential and the renormalization-group improvement of these conditions is also presented. The stability of the tree level minimum of the scalar potential in connection with electric charge conservation and its behaviour under CP is analysed. The question of CP violation is addressed in detail, including the cases of explicit CP violation and spontaneous CP violation. We present a detailed study of weak basis invariants which are odd under CP. These invariants allow for the possibility of studying the CP properties of any two-Higgs-doublet model in an arbitrary Higgs basis. A careful study of spontaneous CP violation is presented, including an analysis of the conditions which have to be satisfied in order for a vacuum to violate CP. We present minimal models of CP violation where the vacuum phase is sufficient to generate a complex CKM matrix, which is at present a requirement for any realistic model of spontaneous CP violation.