arXiv subjects

Shunsuke Yasunaga

Publications and source records attributed to Shunsuke Yasunaga.

6 recordsLinked to original sources

arXiv2026

Hyperon-nucleon interaction through the $K^-d\toπΛN$ reaction

The hyperon-nucleon interaction is investigated through the final-state interaction in the $K^-d\toπ^-Λp$ reaction. We focus on the $ΛN$-$ΣN$ coupled-channel interaction, which produces characteristic structures around the $ΣN$ thresholds in the $Λp$ invariant mass spectrum. The spin-triplet $ΣN\toΛp$ conversion amplitude is constructed within the $K$-matrix formalism using scattering lengths in the isospin basis. We first examine the dependence of the conversion amplitude on the $ΣN$ scattering lengths and find that the threshold structure is particularly sensitive to the sign of the real part of the $I=1/2$ scattering length. We then calculate the $Λp$ invariant mass spectrum of the $K^-d\toπ^-Λp$ reaction, including the contributions from the background diagrams. The resulting spectra show characteristic structures around the $ΣN$ thresholds, whose shapes depend on the choice of the interaction parameters. These results suggest that the $Λp$ invariant mass spectrum can serve as a useful observable for constraining the $ΛN$-$ΣN$ coupled-channel interaction.

nucl-th↗

arXiv2026

Parameter Optimization of Domain-Wall Fermion using Machine Learning

We study a parameter optimization of domain-wall fermions to improve chiral symmetry based on machine learning. Domain-wall fermions involve coefficients along the fifth dimension, which can be treated as trainable parameters to reduce the chiral symmetry violation caused by the finite extent of the fifth dimension. As the loss function, we use the residual mass estimated stochastically on a single gauge configuration. Numerical tests on a $L^3\times T\times L_5=4^3\times8\times8$ lattice demonstrate the feasibility of this framework.

hep-lat↗

arXiv2025

Isotone Chain Study of $\bar{p}$-atom spectroscopy and Strong Spin-orbit splittings

Antiprotonic atoms have served as a pivotal tool for investigating the properties of baryon-baryon interactions, including their spin dependence. Examining the spin-orbit splittings induced by their strong interactions also could help clarify the nature of the $\bar{p}$-nucleus interactions and their fraction mediated by scalar and vector mesons. Although the strong spin-orbit splittings for a certain nucleus have been observed experimentally, thorough theoretical investigations have not yet been conducted. In this study, theoretical calculations based on the Dirac equation are systematically performed for nuclei along several isotone ``chains''. As a result, it is found that the magnitude of the strong spin-orbit splittings exhibits a significant dependence not only on the corresponding level shifts and widths almost linearly, but also on whether the optical potential enters as a vector or scalar potential. A simple perturbative analysis indicates that the relativistic corrections have a dominant effect the magnitude of the splittings. These results are expected to provide deeper insights into $\bar{p}$-nucleus interactions, and by extension baryon-baryon interactions, as well as into the properties of the mesons that mediate them.

hep-ph↗

arXiv2025

Interrelation between $\bar{p}$-Ca Atom Spectra and Nuclear Density Profiles

This work studies $\bar{p}$-Ca atom spectra in light of the strong shifts and level widths, using the optical model with several types of parametric coefficients. The spectroscopic quantities are obtained as the eigenvalues of the Dirac equation, where the nuclear densities computed via nuclear Density Functional Theory and the effect of the anomalous magnetic moment are incorporated. The results indicate that the isovector term's contribution to the optical potential is crucial for explaining the systematical differences in the strong shifts between $^{40}$Ca and $^{48}$Ca. Furthermore, it is found that both the strong shifts and the level widths exhibit significant dependence on the nuclear density profiles. These findings provide critical insights into the nuclear structures, particularly in the context of Calcium isotopes, by offering a more comprehensive understanding of the underlying nuclear-hadron properties.

nucl-th↗

arXiv2025

Theoretical study of the $ΣN$ cusp in the $K^-d\rightarrowπΛN$ reaction

The $K^-d\rightarrowπΛN$ reaction is useful for exploring the hyperon-nucleon interaction through final state interactions. In particular, the cusp structure of the $ΛN$ invariant mass spectrum at the $ΣN$ threshold contains information about the s-wave interaction of 1/2-isospin hyperon-nucleon systems. The calculation of the spectrum is performed with the aim of extracting the scattering length of the $ΣN(I=1/2)$ channel that couples to the $ΛN$ channel from this reaction, and the results are discussed in comparison with experimental data to highlight the factors that should be considered.

nucl-th↗

arXiv2024

$K^-d\rightarrowπΛN$ reaction with in-flight kaons for studying the $ΛN$ interaction

The $ΛN$ invariant mass spectra for the reactions $K^-d\rightarrowπ^-Λp$ and $K^-d\rightarrowπ^0Λn$ are calculated for experimental study of isospin symmetry breaking in the $ΛN$ scattering at low energies, the difference in the scattering lengths and effective ranges of $Λp$ and $Λn$ systems. The calculations are performed for in-flight kaons with a momentum of 1000 MeV/c with employing partial wave analysis up to the p-wave for meson-baryon amplitudes and the spin-flip term for baryon-baryon amplitudes. Kinematic selection is utilized to suppress the background processes by selecting forward-emitting pions and higher momentum nucleons. It is worth noting that isospin symmetry breaking in the $ΛN$ system can be extracted from the difference of the $ΛN$ invariant mass spectra between the $K^-d\rightarrowπ^-Λp$ and $K^-d\rightarrowπ^0Λn$ reactions.

nucl-th↗