We derive the most general sets of viable mass spectra of the exotic Higgs bosons in the Georgi-Machacek model that are consistent with the theoretical constraints of vacuum stability and perturbative unitarity and the experimental constraints of electroweak precision observables, Zbb coupling and Higgs boson signal strengths. Branching ratios of various cascade decay channels of the doubly-charged Higgs boson in the 5 representation, the singly-charged Higgs boson in 3, and the singlet Higgs boson are further computed. As one of the most promising channels for discovering the model, we study the prospects for detecting the doubly-charged Higgs boson that is produced via the vector boson fusion process and decays into final states containing a pair of same-sign leptons at the 14-TeV LHC and a 100-TeV future pp collider. For this purpose, we evaluate acceptance times efficiency for signals of the doubly-charged Higgs boson with general viable mass spectra and compare it with the standard model background estimates.

We consider a model based on the supersymmetric QCD theory with N c = 2 and N f = 3. The theory is strongly coupled at the infrared scale Λ H . Its low energy effective theory below Λ H is described by the supersymmetric standard model with the Higgs sector that contains four iso-spin doublets, two neutral iso-spin singlets and two charged iso-spin singlets. If Λ H is at the multi-TeV to 10 TeV, coupling constants for the F-terms of these composite fields are relatively large at the electroweak scale. Nevertheless, the SM-like Higgs boson is predicted to be as light as 125 GeV because these F-terms contribute to the mass of the SM-like Higgs boson not at the tree level but at the one-loop level. A large non-decoupling effect due to these F-terms appears in the one-loop correction to the triple Higgs boson coupling, which amounts to a few tens percent. Such a non-decoupling property in the Higgs potential realizes the strong first order phase transition, which is required for a successful scenario of electroweak baryogenesis.Recently, the ATLAS and CMS experiments at the LHC [1] have reported an excess in the gamma-gamma mode at about 125 GeV, which may be a signal of the Higgs boson. In the Standard Model (SM), a light Higgs boson is the evidence of the weakly coupled Higgs sector. In models for physics beyond the SM, however, the light Higgs boson does not always correspond to a weakly coupled theory. The scenario based on little Higgs models [2] is an example of a strongly coupled theory with a light Higgs boson, where the Higgs boson arises as a pseudo Nambu-Goldstone boson originating from the breaking of some strongly interacting global symmetry at the TeV scale, and the Higgs boson mass is kept to be light. Supersymmetry (SUSY) is one of the most attractive candidates for the physics beyond the SM. SUSY can solve the gauge hierarchy problem, as the quadratic divergence in the radiative correction to the Higgs boson mass is cancelled owing to the non-renormalization theorem.In addition, elementary scalar fields are automatically introduced in the SUSY theory. The Higgs sector of the minimal SUSY extension of the SM (MSSM) necessarily contains two Higgs doublets. In the MSSM, the coupling constants in the Higgs potential are determined by the electroweak gauge couplings, and the mass of the SM-like Higgs boson is less than the Z boson mass at the tree level. With significant radiative corrections due to the large top Yukawa coupling [3], the Higgs mass can be pushed up to around 125 GeV in the case of very large stop masses or very large left-right stop mixing.Even within the framework based on SUSY, models with strongly coupled light Higgs boson can be constructed. A possible way is to introduce additional R-parity-even chiral superfields which strongly couple to the Higgs sector but the F-terms of which do not contribute to the Higgs boson four-point coupling. In this case, the SM-like Higgs boson is kept to be light. The strong couplings have rich phenomenological implications. First, radiative corrections...

The Standard Model prediction for / based on recent lattice QCD results exhibits a tension with the experimental data. We solve this tension through W + R gauge boson exchange in the SU (2) L × SU (2) R × U (1) B−L model with 'charge symmetry', whose theoretical motivation is to attribute the chiral structure of the Standard Model to the spontaneous breaking of SU (2) R × U (1) B−L gauge group and charge symmetry. We show that M W R < 58 TeV is required to account for the / anomaly in this model. Next, we make a prediction for the neutron EDM in the same model and study a correlation between / and the neutron EDM. We confirm that the model can solve the / anomaly without conflicting the current bound on the neutron EDM, and further reveal that almost all parameter regions in which the / anomaly is explained will be covered by future neutron EDM searches, which leads us to anticipate the discovery of the neutron EDM.

We consider a light supersymmetric top quark (stop) scenario, where a stop and a neutralino are the lightest supersymmetric particles and the stop mass is close to the sum of the neutralino mass and the top quark mass. In this scenario, the top quark and the neutralino coming from the decay of a stop have almost equal velocity vectors, and hence the missing transverse momentum in stop pair production events at colliders is suppressed, which makes the stop search challenging, as in the degenerate scenario where the stop mass and the neutralino mass are nearby. In this paper, we propose a novel analysis technique aiming at discovering the stop pair production signal in such an 'equal-velocity' scenario. The key is to look for events where the missing transverse momentum vector is proportional to the transverse momentum vector of the top quark pair with specific values for the proportionality coefficient, as this coefficient equals to the ratio of the neutralino mass over the top quark mass in the equal-velocity limit. We examine the possibility that the stop signal can be identified at the √ s = 14 TeV LHC by our analysis method.

Abstract:We discuss a strongly-coupled extended Higgs sector with the 126 GeV Higgs boson, which is a low-energy effective theory of the supersymmetric SU(2) H gauge thoery that causes confinement. In this effective theory, we study the parameter region where electroweak phase transition is of strongly first order, as required for successful electroweak baryogenesis. In such a parameter region, the model has a Landau pole at the order of 10 TeV, which corresponds to the confinement scale of the SU(2) H gauge theory. We find that the large coupling constant which blows up at the Landau pole results in large non-decoupling loop effects on low-energy observables, such as the Higgs-photon-photon vertex and the triple Higgs boson vertex. As phenomenological consequences of electroweak baryogenesis in our model, the Higgs-to-diphoton branching ratio is about 20% smaller while the triple Higgs boson coupling is more than about 20% larger than the standard model predictions. Such deviations may be detectable in future collider experiments.

The Georgi-Machacek model extends the standard model Higgs sector by adding two isospin triplet scalar fields and imposing global SU(2) R symmetry on them. A feature of the model is that the triplets can acquire a large vacuum expectation value without conflicting with the current experimental bound on the ρ parameter. We investigate the electroweak phase transition in the Georgi-Machacek model by evaluating the finite-temperature effective potential of the Higgs sector. The electroweak phase transition can be sufficiently strong in a large parameter space when the triplets acquire a vacuum expectation value of O (10) GeV, opening a possibility to realize successful electroweak baryogenesis.

W bosons produced at high transverse momentum in hadron collisions can have polarization along the direction perpendicular to the production plane, which is odd under naïve T reversal where both the threemomenta and angular momenta are reversed. Perturbative QCD predicts nonzero polarization at the one-loop level, which can be measured as parity-odd components in the angular distribution of charged leptons from the decay of W bosons. We perform a detector-level simulation with the generator MADGRAPH5_AMC@NLO, and demonstrate that the asymmetry can be observed at the 8 TeV LHC with 20 fb −1 of data. If confirmed, it will be the first experimental measurement of the sign of the imaginary part of one-loop QCD amplitudes.

We consider a toy model of dark matter with a gauge singlet Dirac fermion that has contact interactions to quarks that differ for right-handed up and down quarks. This is motivated by the isospin-violating dark matter scenario that was proposed to reconcile reported hints of direct dark matter detection with bounds from nonobservation of the signal in other experiments. We discuss how the effects of isospin violation in these couplings can be observed at the LHC. By studying events with large missing transverse momentum (E T ), we show that the ratio of monophoton and monojet events is sensitive to the ratio of the absolute values of the couplings to the up and down quarks, while a dedicated study of dijet plus E T events can reveal their relative sign. We also consider how our results are modified if, instead of a contact interaction, a particle that mediates the interaction is introduced. Our methods have broad applicability to new physics that involves unequal couplings to up and down quarks.