Pyungwon Ko

Scale invariant extension of the standard model with a strongly interacting hidden sector.

We present a scale invariant extension of the standard model with a new QCD-like strong interaction in the hidden sector. A scale Λ(H) is dynamically generated in the hidden sector by dimensional transmutation, and chiral symmetry breaking occurs in the hidden sector. This scale is transmitted to the SM sector by a real singlet scalar messenger S and can trigger electroweak symmetry breaking. Thus all the mass scales in this model arise from the hidden sector scale Λ(H), which has quantum mechanical origin. Furthermore, the lightest hadrons in the hidden sector are stable by the flavor conservation of the hidden sector strong interaction, and could be the cold dark matter (CDM). We study collider phenomenology, relic density, and direct detection rates of the CDM of this model.

Model independent analysis of the forward-backward asymmetry of top quark production at the Tevatron

Abstract Motivated by a possible anomaly in the forward–backward (FB) asymmetry of top quark ( A FB ) observed at the Tevatron, we perform a model independent analysis on q q ¯ → t t ¯ using an effective Lagrangian with dim-6 four-quark operators. We derive necessary conditions on new physics structures and the couplings that are consistent with the t t ¯ production cross section and A FB measured at the Tevatron, and discuss possible new physics scenarios that could generate such dim-6 operators.

νΛMDM: A model for sterile neutrino and dark matter reconciles cosmological and neutrino oscillation data after BICEP2

Abstract We propose an ultraviolet complete theory for cold dark matter (CDM) and sterile neutrinos that can accommodate both cosmological data and neutrino oscillation experiments within 1 σ level. We assume a new U ( 1 ) X dark gauge symmetry which is broken at ∼ O ( MeV ) scale resulting light dark photon. Such a light mediator for DMs self-scattering and scattering-off sterile neutrinos can resolve three controversies for cold DM on small cosmological scales: cusp vs. core , too-big-to-fail and missing satellites . We can also accommodate ∼ O ( 1 ) eV scale sterile neutrinos as the hot dark matter (HDM) and can fit some neutrino anomalies from neutrino oscillation experiments within 1 σ . Finally, the right amount of HDM can make a sizable contribution to dark radiation, and also helps to reconcile the tension between the data on the tensor-to-scalar ratio reported by Planck and BICEP2 Collaborations.

Electroweak symmetry breaking and cold dark matter from strongly interacting hidden sector

We consider a hidden sector with a vectorlike confining gauge theory like QCD with Nh,c colors and Nh,f light quarks Qh in the hidden sector. Then a scale ΛH would be generated by dimensional transmutation, and chiral symmetry breaking occurs in the hidden sector. This scale ΛH can play a role of the SM Higgs mass parameter, triggering electroweak symmetry breaking (EWSB). Furthermore the lightest mesons in the hidden sector is stable by flavor conservation of the hidden sector strong interaction, and could be a good cold dark matter (CDM). We study collider phenomenology, and relic density and direct detection rates of the CDM of this model.

Implications of LHC data on 125 GeV Higgs-like boson for the Standard Model and its various extensions

A bstractRecent data on 125 GeV Higgs-like boson at the LHC start to constrain the electroweak symmetry breaking (EWSB) sector of the Standard Model (SM) and its various extensions. If one imposes the local gauge symmetry of the SM (SU(3)c × SU(2)L × U(1)Y) to any possible new physics scenarios, the SM Higgs properties will be modified by intrinsically two ways: by new physics either coupling directly to the SM Higgs boson h, or affecting indirectly the SM Higgs properties through the mixing of h with a SM singlet scalar s. (Here s is a singlet under the SM gauge group, but may be charged under a new gauge charge and can have nonrenormalizable couplings to non-SM particles.) The models of two Higgs doublets, extra sequential and mirror fermions belong to the first category, whereas the models with a hidden sector dark matter, extra vector-like fermions and new charged vector bosons, which can enhance the diphoton rate of the SM Higgs-like resonance, belong to the second category. We perform a global fit to data in terms of the effective Lagrangian description of two interaction eigenstates of scalar bosons, a SM Higgs and a singlet scalar, and their mixing. This framework is more suitable to study singlet-extended scenarios discussed above compared to other approaches based on the Lagrangian of mass eigenstates. With fairly model-independent assumptions, the effective Lagrangian contains at most four free parameters still encompassing the majority of models in the literature. Interestingly, the SM gives the best fit if all data from ATLAS and CMS are used, whereas various singlet extensions can fit better to individual ATLAS or CMS data. Without further assumptions, an upper bound on the total width (or, non-standard branching ratio) is generically obtained. Furthermore, the global fit based on our parameterization can be used to probe interactions of the singlet scalar if the singlet resides below 2mW.

PROBING SUPERSYMMETRY-INDUCED CP VIOLATION AT B FACTORIES

In the minimal supersymmetric standard model (MSSM), the \mu-parameter and the trilinear coupling A_t may be generically complex and can affect various observables at B factories. Imposing the edm constraints, we find that there is no new large phase shift in the B^0 - \bar{B^0} mixing, CP violating dilepton asymmetry is smaller than 0.1 %, and the direct CP violation in B\to X_s \gamma can be as large as \sim \pm 16 %.

Stable Higgs bosons as cold dark matter

Abstract In a class of the gauge–Higgs unification models the 4D neutral Higgs boson, which is a part of the extra-dimensional component of the gauge fields, becomes absolutely stable as a consequence of the gauge invariance and dynamically generated new parity, serving as a promising candidate for cold dark matter (CDM). We show that the observed relic abundance of cold dark matter is obtained in the SO ( 5 ) × U ( 1 ) model in the warped space with the Higgs mass around 70 GeV. The Higgs–nucleon scattering cross section is found to be close to the current CDMS II and XENON10 bounds in the direct detection of dark matter.

B → D (*) τν and B → τν in chiral U(1)′ models with flavored multi Higgs doublets

A bstractWe discuss semileptonic and leptonic B decays, B → D(∗)τν and B → τν, in the chiral U(1)′ models which were proposed by the present authors in the context of the top forward-backward asymmetry

Longitudinal top polarization as a probe of a possible origin of forward–backward asymmetry of the top quark at the Tevatron

\left( {A_{\mathrm{FB}}^t} \right)

More on R-parity and lepton family number violating couplings from muon(ium) conversion, and tau and pi0 decays

observed at the Tevatron. In these models, extra Higgs doublets with nonzero U(1)′ charges are required in order to make the realistic mass matrix for up-type quarks. Then the extra (pseudo)scalars contribute to