Narrow Results

We study the kaon photoproduction associated with the production of the ground state Λ. We investigate the role of K and K* exchange in the t-channel, which can be tested by the photon asymmetry in comparison with experimental data. We find a significant amount of contribution from the one-loop diagram induced by the gauged Wess-Zumino-Witten term for QCD anomaly. This enable us to use coupling constants which are determined in a microscopic way, unlike the previous phenomenological studies where the K* coupling strengths were treated as a free parameter.

Using the effective Lagrangian method, we analyze the corrections to the branching ratio b→sγ from the Higgs sector in the standard model. The numerical result indicates that the corrections from this sector to b→sγ is about -2% as m_h~ 0.5 TeV.

Possible nonstandard tuZ and tcZ interactions, which induce flavor-changing neutral-current decays of the top quark, are studied in the effective-Lagrangian framework. The corresponding Lagrangian consists of four kinds of nonstandard couplings coming from $SU(3)\times SU(2)\times U(1)$ invariant dimension-6 effective operators. The four coupling constants in each interaction are treated as complex numbers independent of each other and constraints on them are derived by using the present experimental limits of the branching fractions for $t\to uZ$ and $t\to cZ$ processes. Future improvements of those constraints are also discussed as well as possibilities of measurements of these couplings at the High-Luminosity Large Hadron Collider.

Recently, we calculated the contribution of Leutwyler zero mode chromons to the Yang–Mills effective Lagrangian by integrating over collective coordinates of the nonlinearly interacting zero modes. Here, we analyze the behavior of the partition function prefactor and the integration measure Jacobian of the zero modes and show that these factors do not contribute to the effective Lagrangian and do not alter the earlier results.

Low energy theorems of Nambu–Goldstone fermion associated with spontaneously broken supersymmetry are studied for gauge supermultiplets. Two possible terms in the effective Lagrangian are needed to deal with massless gaugino and/or massless gauge boson. As an illustrative example, a concrete model is worked out which can interpolate massless as well as massive gaugino and/or gauge boson to examine the low energy effective interaction of NG-fermion.

In this contribution the tree-level effective actions for gluons and gravitons, as derived from Open and Closed Superstring theories, are reviewed respectively. As known for a long time, at zero order in α′ (the string fundamental constant) the first action is pure Yang-Mills while the second one is pure Einstein-Hilbert. The first Superstring Theory corrections turn up to appear at order in the first case while they appear at in the second one, as known from the three and four-point scattering amplitudes for gluons and gravitons, respectively. Recent work involving the order contributions to the Yang-Mills action is reviewed with some detail, including the authors' present line of research. Also, the uncharted territory of five graviton scattering is commented, looking forward to derive the Superstring Theory corrections to the Einstein-Hilbert action.

The axions and axion-like particles can be detected via a resonant atomic or molecular transition induced by axion absorption. The signal obtained in this process is second order in the axion-electron interaction constant and hence small. In this chapter, it is demonstrated that this signal may become first order in the axion-electron interaction constant if we allow the interference between the axion-induced transition amplitude and the transition amplitude induced by the electromagnetic radiation. Additionally, we show that the conventional scheme of producing axions from photons in a magnetic field may be improved if the field is replaced by an atomic medium in which photons scattering off the atoms in the forward direction are transformed into axions.

We employ QCD sum rules to calculate the J/ψ form factors and coupling constants with charmed mesons, by studying three-point correlation functions. In particular, we consider the J/ψD*D and J/ψDD vertices. We determine the momentum dependence of the form factors for kinematical conditions where J/ψ, D or D* are off-shell. Extrapolating to the pole of each of the form factors obtained, we determine the coupling constants. For both couplings, our results (within the errors) are compatible with estimates based on the constituent quark model.

About two decades ago, Gerry Brown pushed me to study hadron physics using hadronic models based on the hidden local symmetry (HLS). Since then, I have been involving many works related to the HLS. In this contribution to Gerry’s memorial, I will summarize my recent analyses associated with the HLS. After a very brief summary of the HLS, I will show a way to determine parameters of the HLS model from holographic QCD models. This model provides a soliton solution which is identified with the nucleon. I will briefly introduce a model in which the solitons are put onto a crystal lattice for simulating nuclear matter. The results suggest existence of the chiral invariant mass of nucleon. I also briefly review my recent analyses on the nuclear matter by using a hadronic model including nucleon field together with the $\pi$, $\sigma$, $\rho$ and $\omega$ mesons based on the parity doublet structure of nucleon combined with the HLS, in which the chiral invariant mass of the nucleon is naturally embedded. The result implies that studying effective masses of nucleons will give a clue for the chiral invariant mass. Finally, I will show our recent analysis on the medium modification of charmed meson masses using a chiral model based on the chiral doubling structure of charmed mesons. The result shows that the masses of the chiral partners of charmed mesons become closer in high density reflecting the particle chiral symmetry restoration in medium.

The mechanism of K* vector meson photoproduction off the proton target, γp → K^*+Λ, is deeply studied by using an effective Lagrangian method. Based on the (t,s,u)-channel Born diagrams, we included higher resonance terms, i.e., S₁₁(2090) and G₁₇(2190), along with the D₁₃(2080) and D₁₅(2200), which are already considered in a previous theoretical analysis. The total and differential cross section are computed and we obtain quite precise results in comparison with the recent CLAS data.

Recently, the observation of the a₀(980)⁰−f₀(980) mixing in the isospin breaking decay J/ψ → ηπ⁰ϕ was reported by the BESIII Collaboration. In the Dalitz plot for that decay with the η reconstructed from two photons, there is a band around 1.4 GeV on the π⁰ϕ distribution. Here, we study the effects of a set of $K^{*}\overline{K}K$ triangle diagrams, and show that due to triangle singularities such diagrams can lead to a peak around 1.4 GeV in the π⁰ϕ invariant mass distribution. To examine whether the band is due to triangle singularities or due to a resonance, more experimental data are needed.

This talk summarizes the present status of the relativistic Hartree-Fock (RHF) approach based on density-dependent effective Lagrangians. This approach keeps all the success of the widely used relativistic Hartree models, but it can also treat the missing effects due to the neglect of the exchange (Fock) terms. These effects are recovered by explicitly including the coupling of nucleons to effective pions and to the tensor component of rho mesons. On some selected examples it will be shown that these effects can be important for nuclear properties such as single-particle spectra in isotopic and isotonic chains, or spin-isospin excitation modes.

By using path integral methods we obtain effective Lagrangians for noncommutative Quantum Mechanics. The starting point is a relatively simple modification of standard phase-space path integrals, which leads in configuration space to Lagrangians depending also on the accelerations. We comment on the subtleties involved.

About two decades ago, Gerry Brown pushed me to study hadron physics using hadronic models based on the hidden local symmetry (HLS). Since then, I have been involving many works related to the HLS. In this contribution to Gerry’s memorial, I will summarize my recent analyses associated with the HLS. After a very brief summary of the HLS, I will show a way to determine parameters of the HLS model from holographic QCD models. This model provides a soliton solution which is identified with the nucleon. I will briefly introduce a model in which the solitons are put onto a crystal lattice for simulating nuclear matter. The results suggest existence of the chiral invariant mass of nucleon. I also briefly review my recent analyses on the nuclear matter by using a hadronic model including nucleon field together with the π, σ, ρ and ω mesons based on the parity doublet structure of nucleon combined with the HLS, in which the chiral invariant mass of the nucleon is naturally embedded. The result implies that studying effective masses of nucleons will give a clue for the chiral invariant mass. Finally, I will show our recent analysis on the medium modification of charmed meson masses using a chiral model based on the chiral doubling structure of charmed mesons. The result shows that the masses of the chiral partners of charmed mesons become closer in high density reflecting the particle chiral symmetry restoration in medium.