Shuntaro Sakai

The η′N interaction from a chiral effective model and η′-N bound state

The η′ mass reduction in the nuclear medium is expected owing to the degeneracy of the pseudoscalar-singlet and octet mesons in the restoration of the spontaneous chiral symmetry breaking. In this study, we investigate the η′N 2body interaction, which is the fundamental interaction of the in-medium η′ properties, using the linear sigma model as a chiral effective model. The η′N interaction in the linear sigma model comes from the scalar meson exchange with U A(1) symmetry effect and is found to be fairly strong attraction. The transition amplitude of η′N to the ηN channel is relatively small compared to that of elastic channel. From the analysis of the η′N 2body system, we find a η′N bound state with the binding energy 12.3-3.3iMeV. We expect that this strongly attractive two body interaction leads to a deep and attractive optical potential.

η′ meson under partial restoration of chiral symmetry in nuclear medium

In-medium modification of the 0 mass is discussed in the context of partial restoration of chiral symmetry in nuclear medium. We emphasize that the UA(1) anomaly e ects causes the 0 - mass di erence necessarily through the chiral symmetry breaking. As a consequence, the 0 mass is expected to be reduced by order of 100 MeV in nuclear matter where about 30% reduction of chiral symmetry takes place. The strong attraction relating to the 0 mass generation eventually implies that there should be also a strong attractive interaction in the scalar channel of the 0 -N two-body system. We find that the attraction can be strong enough to form a

Investigation of the η′N system using the linear sigma model

In this paper, we investigate the η′N system using the three-flavor linear sigma model including the effect of flavor SU(3) symmetry breaking. The η′N bound state is also found in the case including flavor symmetry breaking and coupling with the ηN and πN channels. The η′N interaction becomes more attractive with the inclusion of flavor symmetry breaking, which causes mixing between the singlet and octet scalar mesons. The existence of such a bound state would have some impact on the η′–nucleus system, which is of interest from both theoretical and experimental viewpoints.

Effect of the final state interaction of

We investigate the η′ photoproduction off the nucleon with a particular interest in the effect of the final-state interaction (FSI) of the η′ meson and nucleon (η′N) based on the three-flavor linear σ model. We find an enhancement in the cross section of the η′ photoproduction near the η′N-threshold energy owing to the η′N FSI. With the η′ meson at forward angles, the energy dependence near the η′N threshold is well reproduced with the η′N FSI. The cross section at backward angles can also be a good probe to investigate the strength of the η′N interaction.

\eta' N

We report our recent project to study the QCD phase diagram by the canonical approach (CA), which is expected to solve the sign problem. First we briefly describe the sign problem and several approaches to fight against it. Then we argue that the CA may be a break-through if we combine it with the multiple precision calculation. We study the method using the hopping parameter expansion (HPE), in order to investigate how the CA works. We show explicitly how we calculate the winding number in HPE and obtain the fugacity expansion whose coefficients are the canonical partition functions. Finally we discuss dark sides of the current CA, which should be beaten for the method to become a real tool of QCD phase explorers.

on the

Erratum: Prog. Theor. Exp. Phys. (2015) 089201. doi: 10.1093/ptep/ptv111. First published online August 6, 2015.

\eta'

Erratum: Prog. Theor. Exp. Phys. (2015) 089201. doi: 10.1093/ptep/ptv111. First published online August 6, 2015.

photoproduction off the nucleon

We investigate the role for the softening of the scalar-isoscalar (sigma) meson in the

Beating the sign problem in finite density lattice QCD

\eta\rightarrow\pi^+\pi^-\pi^0

The η decay into 3π in asymmetric nuclear medium

and