Sin Kyu Kang

Comprehensive study of two Higgs doublet models in light of the new boson with mass around 125 GeV

A bstractA new boson of mass roughly 125 GeV has been recently reported by the ATLAS and CMS collaborations. Although its signals in various decay modes resemble those of the standard model (SM) Higgs boson, observed are the combinations of entangled information about the production, decay rates and total decay width of the new boson. In addition, some decay channels show non-negligible deviation from the SM expectation, such as the 2σ excess in the diphoton channel. In the four types (I, II, X and Y) of two Higgs doublet models, we perform the global χ2 fit in three scenarios: (i) the new boson is the light CP-even Higgs boson h0; (ii) it is the heavy CP-even Higgs boson H0; (iii) the signals are from the degenerate state of h0 and the pseudoscalar A0. Considering other phenomenological constraints such as flavor physics, electroweak precision data, and the LEP search for the Higgs boson, we find that the first scenarios in Type II provides the best fit. And the other models are also as good as the SM in explaining the LHC Higgs data.

Importance of threshold corrections in quark–lepton complementarity

Abstract The recent experimental measurements of the solar neutrino mixing angle θ sol and the Cabibbo mixing angle θ C reveal a surprising relation, θ sol + θ C ≃ π 4 . We note that the lepton mixing matrix derived from quark–lepton unification can lead to a shift of the complementarity relation at low energy. While the renormalization group effects generally lead to additive contribution on top of the shift, in this Letter, we show that the threshold corrections which may exist in some intermediate scale new physics such as supersymmetric standard model can diminish it, so we can achieve the complementarity relation at a low energy. Finally, we discuss a possibility to achieve the complementarity relation at a high energy by taking particular form of non-symmetric form of down Yukawa matrix.

Minimal seesaw model with tri/bi-maximal mixing and leptogenesis

Abstract We examine minimal seesaw mechanism in which the masses of light neutrinos are described with tri/bi-maximal mixing in the basis where the charged-lepton Yukawa matrix and heavy Majorana neutrino mass matrix are diagonal. We search for all possible Dirac mass textures which contain at least one zero entry in 3 × 2 matrix and evaluate the corresponding lepton asymmetries. We present the baryon asymmetry in terms of a single low energy unknown, a Majorana CP phase to be clued from neutrinoless double beta decay.

Correlation between lepton flavor violation and B(d,s)–B¯(d,s) mixing in SUSY GUT

Abstract Motivated by the recent measurements of the B s − B ¯ s mass difference from the DO and CDF Collaborations, we probe new physics effects in the B q − B ¯ q mixing within the context of the supersymmetric grand unified model (SUSY GUT). We find that new physics effects in B s ( d ) − B ¯ s ( d ) mixing lead to the correlated information in the branching fractions of the lepton flavor violating decays, which may serve as a test of the SUSY GUT. We also discuss the implication of such new physics effects on the quark–lepton complementarity in the neutrino mixings.

Four-Neutrino Analysis of 1.5 km Baseline Reactor Antineutrino Oscillations

The masses of sterile neutrinos are not yet known, and depending on the orders of magnitudes, their existence may explain reactor anomalies or the spectral shape of reactor neutrino events at 1.5 km baseline detector. Here, we present four-neutrino analysis of the results announced by RENO and Daya Bay, which performed the definitive measurements of based on the disappearance of reactor antineutrinos at km order baselines. Our results using 3

Implications of SNO and BOREXINO results on neutrino oscillations and Majorana magnetic moments

Abstract Using the recent measurement of SNO salt phase experiment, we investigate how much the solar neutrino flux deficit observed at SNO could be due to ν e transition into antineutrino. Our analysis leads to rather optimistic conclusion that the SNO salt phase data may indicate the existence of Majorana magnetic moment. The prospect for the future BOREXINO experiment is also discussed.

Are deviation from bi-maximal mixing and non-zero Ue3 related to non-degeneracy of heavy Majorana neutrinos?

Abstract We propose a scenario that the mass splitting between the first generation of the heavy Majorana neutrino and the other two generations of degenerate heavy neutrinos in the seesaw framework is responsible for the deviation of the solar mixing angle from the maximal mixing, while keeping the maximal mixing between the tau and muon neutrinos as it is. On top of the scenario, we show that the tiny breaking of the degeneracy of the two heavy Majorana neutrinos leads to the non-zero small mixing angle U e 3 in the PMNS matrix and the little deviation of the atmospheric neutrino mixing angle from the maximal mixing.

Dark matter signals and cosmic ray anomalies in an extended seesaw model

Abstract An extended seesaw model proposed to achieve low scale leptogenesis can resolve the excess positron and electron fluxes observed from PAMELA, ATIC and/or Fermi-LAT, and simultaneously accommodate some of recent experimental results for dark matter (DM) signals. In this approach, in addition to SU ( 2 ) L doublet and the (light) singlet Higgs fields, an extra vector-like singlet neutrino and a singlet scalar field, which are coexisting two-particle dark matter candidates, are responsible for the origin of the excess positron and electron fluxes to resolve the PAMELA, ATIC and/or Fermi-LAT anomalies, as well as for the DM signals observed from direct searches in low mass scale.