Pion Exchange Interaction in Bonn Potential and Relativistic and Non-relativistic Framework in Nuclear Matter

As the residual interaction of quantum chromodynamics in low-energy region, the nucleon-nucleon (NN) potential can only be exactly described by the model picture now. In the Bonn potential, one of the most well-known NN interaction models, the nucleons interact with each other through exchanging the pion and several heavier mesons, where the pion plays an essential role. It provides a partial contribution of tensor force in the intermediate-range region and the main component in the long-range region in NN potential. However, it is very difficult to be treated in the nuclear many-body system due to its pseudovector or pseudoscalar property. Recently, three high-precision charge-dependent Bonn potentials were proposed with pseudovector coupling types and different pion-nucleon coupling strengths and applied them to study the properties of nuclear matter and neutron stars in the non-relativistic and relativistic frameworks. Furthermore, to properly deal with the strong short-range repulsion and tensor force of the NN potential, some new relativistic {\it ab initio} methods have also been developed in the past decade to discuss the role of pion and relativistic effects in nuclear matter.Comment: 29 pages, 12 figures, 6 tables. Contribution to the "Handbook of Nuclear Physics", Springer Nature, 2022, Eds. I. Tanihata, H. Toki and T. Kajin

Nuclear Matter and Neutron Stars from Relativistic Brueckner-Hartree-Fock Theory

The momentum and isospin dependence of the single-particle potential for the in-medium nucleon are the key quantities in the Relativistic Brueckner-Hartree-Fock (RBHF) theory. It depends on how to extract the scalar and the vector components of the single-particle potential inside nuclear matter. In contrast to the RBHF calculations in the Dirac space with the positive-energy states (PESs) only, the single-particle potential can be determined in a unique way by the RBHF theory together with the negative-energy states (NESs), i.e., the RBHF theory in the full Dirac space. The saturation properties of symmetric and asymmetric nuclear matter in the full Dirac space are systematically investigated based on the realistic Bonn nucleon-nucleon potentials. In order to further specify the importance of the calculations in the full Dirac space, the neutron star properties are investigated. The direct URCA process in neutron star cooling will happen at density $\rho_{\rm{DURCA}}=0.43,~0.48,~0.52$ fm$^{-3}$ with the proton fractions $Y_{p,\rm{DURCA}}=0.13$. The radii of a $1.4M_\odot$ neutron star are predicated as $R_{1.4M_\odot}=11.97,~12.13,~12.27$ km, and their tidal deformabilities are $\Lambda_{1.4M_\odot}=376,~405,~433$ for potential Bonn A, B, C. Comparing with the results obtained in the Dirac space with PESs only, full-Dirac-space RBHF calculation predicts the softest symmetry energy which would be more favored by the gravitational waves (GW) detection from GW170817. Furthermore, the results from full-Dirac-space RBHF theory are consistent with the recent astronomical observations of massive neutron stars and simultaneous mass-radius measurement

Properties of 208^{208}Pb predicted from the relativistic equation of state in the full Dirac space

Relativistic Brueckner-Hartree-Fock (RBHF) theory in the full Dirac space allows one to determine uniquely the momentum dependence of scalar and vector components of the single-particle potentials. In order to extend this new method from nuclear matter to finite nuclei, as a first step, properties of $^{208}$Pb are explored by using the microscopic equation of state for asymmetric nuclear matter and a liquid droplet model. The neutron and proton density distributions, the binding energies, the neutron and proton radii, and the neutron skin thickness in $^{208}$Pb are calculated. In order to further compare the charge densities predicted from the RBHF theory in the full Dirac space with the experimental charge densities, the differential cross sections and the electric charge form factors in the elastic electron-nucleus scattering are obtained by using the phase-shift analysis method. The results from the RBHF theory are in good agreement with the experimental data. In addition, the uncertainty arising from variations of the surface term parameter $f_0$ in the liquid droplet model is also discussed

Isospin splitting of the Dirac mass probed by the relativistic Brueckner-Hartree-Fock theory in the full Dirac space

The isospin splitting of the Dirac mass obtained with the relativistic Brueckner-Hartree-Fock (RBHF) theory is thoroughly investigated. From the perspective in the full Dirac space, the long-standing controversy between the momentum-independence approximation (MIA) method and the projection method on the isospin splitting of the Dirac mass in asymmetric nuclear matter (ANM) is analyzed in detail. We find that, the \textit{assumption procedure} of the MIA method, which assumes that the single-particle potentials are momentum independent, is not a sufficient condition that directly leads to the wrong sign of the isospin splitting of the Dirac mass, while the \textit{extraction procedure} of the MIA method, which extracts the single-particle potentials from the single-particle potential energy, leads to the wrong sign. By approximately solving the set of equations involved in the \textit{extraction procedure}, a formal expression of the Dirac mass is obtained. The wrong isospin splitting of the Dirac mass is mainly caused by that the \textit{extraction procedure} forcely assumes the momentum dependence of the single-particle potential energy to be a quadratic form where the strength is solely determined by the constant scalar potential.Comment: 13 pages, 4 figure

Neutron-proton effective mass splitting in neutron-rich matter

Nucleon effective masses in neutron-rich matter are studied with the relativistic Brueckner-Hartree-Fock (RBHF) theory in the full Dirac space. The neutron and proton effective masses for symmetric nuclear matter are 0.80, which agrees well with the empirical values. In neutron-rich matter, the effective mass of the neutron is found larger than that of the proton, and the neutron-proton effective mass splittings at the empirical saturation density are predicted as $0.187\alpha$ with $\alpha$ being the isospin asymmetry parameter. The result is compared to other ab initio calculations and is consistent with the constraints from the nuclear reaction and structure measurements, such as the nucleon-nucleus scattering, the giant resonances of $^{208}$Pb, and the Hugenholtz-Van Hove theorem with systematics of nuclear symmetry energy and its slope. The predictions of the neutron-proton effective mass splitting from the RBHF theory in the full Dirac space might be helpful to constrain the isovector parameters in phenomenological density functionals.Comment: 14 pages, 4 figure

日本の公共図書館におけるTwitter広報活動と図書館利用量の因果推論

筑波大学University of Tsukuba修士（情報学）Master of Library and Information Studies2022master thesi

Genome-wide analysis of the Populus trichocarpa laccase gene family and functional identification of PtrLAC23

IntroductionBiofuel is a kind of sustainable, renewable and environment friendly energy. Lignocellulose from the stems of woody plants is the main raw material for “second generation biofuels”. Lignin content limits fermentation yield and is therefore a major obstacle in biofuel production. Plant laccase plays an important role in the final step of lignin formation, which provides a new strategy for us to obtain ideal biofuels by regulating the expression of laccase genes to directly gain the desired lignin content or change the composition of lignin.MethodsMultiple sequence alignment and phylogenetic analysis were used to classify PtrLAC genes; sequence features of PtrLACs were revealed by gene structure and motif composition analysis; gene duplication, interspecific collinearity and Ka/Ks analysis were conducted to identify ancient PtrLACs; expression levels of PtrLAC genes were measured by RNA-Seq data and qRT-PCR; domain analysis combine with cis-acting elements prediction together showed the potential function of PtrLACs. Furthermore, Alphafold2 was used to simulate laccase 3D structures, proLAC23::LAC23-eGFP transgenic Populus stem transects were applied to fluorescence observation.ResultsA comprehensive analysis of the P. trichocarpa laccase gene (PtLAC) family was performed. Some ancient PtrLAC genes such as PtrLAC25, PtrLAC19 and PtrLAC41 were identified. Gene structure and distribution of conserved motifs clearly showed sequence characteristics of each PtrLAC. Combining published RNA-Seq data and qRT-PCR analysis, we revealed the expression pattern of PtrLAC gene family. Prediction results of cis-acting elements show that PtrLAC gene regulation was closely related to light. Through above analyses, we selected 5 laccases and used Alphafold2 to simulate protein 3D structures, results showed that PtrLAC23 may be closely related to the lignification. Fluorescence observation of proLAC23::LAC23-eGFP transgenic Populus stem transects and qRT-PCR results confirmed our hypothesis again.DiscussionIn this study, we fully analyzed the Populus trichocarpa laccase gene family and identified key laccase genes related to lignification. These findings not only provide new insights into the characteristics and functions of Populus laccase, but also give a new understanding of the broad prospects of plant laccase in lignocellulosic biofuel production

Hadron-quark phase transition in neutron star by combining the relativistic Brueckner-Hartree-Fock theory and Dyson-Schwinger equation approach

Starting from the relativistic Brueckner-Hartree-Fock theory for nuclear matter and the Dyson-Schwinger equation approach for quark matter, the possible hadron-quark phase transition in the interior of a neutron star is explored. The first-order phase transition and crossover are studied by performing the Maxwell construction and three-window construction respectively. The mass-radius relation and the tidal deformability of the hybrid star are calculated and compared to the joint mass-radius observation of a neutron star and the constraints from gravitational wave detection. For the Maxwell construction, no stable quark core is found in the interior of a neutron star. For the three-window construction, the parameters of the smooth interpolation function are chosen in such a way to keep the thermodynamic stability and lead to a moderate crossover density region. To support a two-solar-mass neutron star under the three-window construction, the effective width of medium screening effects in quark matter should be around $0.35$ GeV.Comment: 27 pages, 12 figures, 2 tables, published on Phys.Rev.D 107, 103009 (2023