Koichi Ohta

Relativistic corrections to the baryon resonance photoexcitation amplitudes in the quark model

Abstract We calculate the relativistic corrections of order (quark mass)−2 to the baryon resonance photoexcitation amplitudes in the harmonic-oscillator quark model. We find that the relativistic effects entail significant consequences and that the agreement with experiment is much improved.

PCAC and renormalization of the weak axial-vector vertex in nuclei

Abstract We reinvestigate a model proposed by Ericson et al. and show that the repulsive hard core in the nucleon-nucleon modifies the weak axial form factor g A as well as the pionic form factor g r of the nucleons in nuclear matter. We also describe the renormalization of the induced pseudoscalar form factor h A .

Yukawa couplings in meson-soliton scattering

Abstract We study the meson-soliton scattering in the two-dimensional o 4 theory. We find that the t -matrix obtained from the linearized equation for the quantum fluctuation part of the meson field contains pole terms. We prove that the pole terms should be interpreted as the Born contributions to the t -matrix. The Yukawa interaction manifests itself as the Born term in the scattering amplitude, its strength being dictated by the classical solution.

Monrigid quantization of soliton and meson-soliton scattering

Abstract We study meson-soliton scattering using a nonrigid quantization scheme recently developed by Verschelde. We show that the sum of the double-pole term in the background scattering and the second-order correction induced by the meson-soliton linear coupling exactly reproduces the Born term in conventional models with an explicit Yukawa coupling.

Stability of the perturbative vacuum against spatial variations of the Polyakov loop

We investigate the effective action of the Polyakov loop with spatial variations. We expand the effective action not in powers of derivatives or momenta, but in powers of variational amplitudes. At one-loop order the results suggest that the instability towards the confining vacuum may be caused by the variational terms.

Isobaric model for the P-wave pion-nucleon scattering volumes in pionic atoms

Abstract The effective Lagrangian model is studied for constraction of the P-wave interaction volumes in free space and in nuclear medium. The mass shift of the N ∗ isobar arising from the Pauli correction and the local field correction is calculated allowing the π and ϱ exchange to be responsible for the NN ∗ → N ∗ N transition potential.

Canonical quantization of gauge fields in static space-times with applications to Rindler spaces

The canonical quantization in the Weyl gauge of gauge fields in static space-times is presented. With an appropriate definition of transverse and longitudinal components of gauge fields, the Gauss law constraint is resolved explicitly for scalar and spinor QED and a complete nonperturbative solution is given for the quantized Maxwell field coupled to external currents. The formalism is applied in investigations of the electromagnetic field in Rindler spaces. The relation of creation and annihilation operators in Minkowski and Rindler spaces is established, and initial value problems associated with bremsstrahlung of a uniformly accelerated charge are studied. The peculiar scaling properties of scalar and gauge theories in Rindler spaces are discussed, and various quantities such as the photon condensate or the interaction energy of static charges and of scalar sources are computed.

Dynamic aspect of the chiral phase transition in the mode coupling theory

Abstract We analyze the dynamic aspect of the chiral phase transition. We apply the mode coupling theory to the linear sigma model and derive the kinetic equation for the chiral phase transition. We challenge Hohenberg and Halperins classification scheme of dynamic critical phenomena in which the dynamic universality class of the chiral phase transition has been identified with that of the antiferromagnet. We point out a crucial difference between the chiral dynamics and the antiferromagnet system. We also calculate the dynamic critical exponent for the chiral phase transition. Our result is z = 1 − η / 2 ≅ 0.98 which is contrasted with z = d / 2 = 1.5 of the antiferromagnet.

Effects of exchange currents on muon capture

Abstract It is shown that the one-pion exchange current renormalizes the axial and induced pseudoscalar form factors of the weak axial current. The effect decreases total muon capture rate about 13% and the branching ratio of radiative-to-ordinary muon capture rate about 12%.

Static interactions and stability of matter in Rindler space

Dynamical issues associated with quantum fields in Rindler space are addressed in a study of the interaction between two sources at rest generated by the exchange of scalar particles, photons, and gravitons. These static interaction energies in Rindler space are shown to be scale invariant, complex quantities. The imaginary part will be seen to have its quantum mechanical origin in the presence of an infinity of zero modes in uniformly accelerated frames which in turn are related to the radiation observed in inertial frames. The impact of a uniform acceleration on the stability of matter and the properties of particles is discussed, and estimates are presented of the instability of hydrogen atoms when approaching the horizon.