A new improved study of K−–proton interactions near threshold is performed using coupled-channels dynamics based on the next-to-leading order chiral SU(3) meson–baryon effective Lagrangian. Accurate ...constraints are now provided by new high-precision kaonic hydrogen measurements. Together with threshold branching ratios and scattering data, these constraints permit an updated analysis of the complex K¯N and πΣ coupled-channels amplitudes and an improved determination of the K−p scattering length, including uncertainty estimates.
In the fight against the pandemic of COVID-19, it is important to ascertain the status and trend of the infection spread quickly and accurately.
The purpose of our study is to formulate a new and ...simple indicator that represents the COVID-19 spread rate by using publicly available data.
The new indicator K is a backward difference approximation of the logarithmic derivative of the cumulative number of cases with a time interval of 7 days. It is calculated as a ratio of the number of newly confirmed cases in a week to the total number of cases.
The analysis of the current status of COVID-19 spreading over countries showed an approximate linear decrease in the time evolution of the K value. The slope of the linear decrease differed from country to country. In addition, it was steeper for East and Southeast Asian countries than for European countries. The regional difference in the slope seems to reflect both social and immunological circumstances for each country.
The approximate linear decrease of the K value indicates that the COVID-19 spread does not grow exponentially but starts to attenuate from the early stage. The K trajectory in a wide range was successfully reproduced by a phenomenological model with the constant attenuation assumption, indicating that the total number of the infected people follows the Gompertz curve. Focusing on the change in the value of K will help to improve and refine epidemiological models of COVID-19.
The nucleon(N)-Omega(Ω) system in the S-wave and spin-2 channel (S25) is studied from the (2+1)-flavor lattice QCD with nearly physical quark masses (mπ≃146MeV and mK≃525MeV). The time-dependent HAL ...QCD method is employed to convert the lattice QCD data of the two-baryon correlation function to the baryon-baryon potential and eventually to the scattering observables. The NΩ(S25) potential, obtained under the assumption that its couplings to the D-wave octet-baryon pairs are small, is found to be attractive in all distances and to produce a quasi-bound state near unitarity: In this channel, the scattering length, the effective range and the binding energy from QCD alone read a0=5.30(0.44)(−0.01+0.16)fm, reff=1.26(0.01)(−0.01+0.02)fm, B=1.54(0.30)(−0.10+0.04)MeV, respectively. Including the extra Coulomb attraction, the binding energy of pΩ−(S25) becomes BpΩ−=2.46(0.34)(−0.11+0.04)MeV. Such a spin-2 pΩ− state could be searched through two-particle correlations in p-p, p-nucleus and nucleus-nucleus collisions.
Most of the exotic resonances observed in the past decade appear as a peak structure near some threshold. These near-threshold phenomena can be interpreted as genuine resonant states or enhanced ...threshold cusps. Apparently, there is no straightforward way of distinguishing the two structures. In this work, we employ the strength of deep feed-forward neural network in classifying objects with almost similar features. We construct a neural network model with scattering amplitude as input and the nature of a pole causing the enhancement as output. The training data is generated by an S-matrix satisfying the unitarity and analyticity requirements. Using the separable potential model, we generate a validation data set to measure the network's predictive power. We find that our trained neural network model gives high accuracy when the cutoff parameter of the validation data is within 400–800 MeV. As a final test, we use the Nijmegen partial wave and potential models for nucleon-nucleon scattering and show that the network gives the correct nature of the pole.
Baryon–baryon potentials are obtained from 3-flavor QCD simulations with the lattice volume L≃4 fm, the lattice spacing a≃0.12 fm, and the pseudo-scalar-meson mass Mps=469–1171 MeV. The NN scattering ...phase-shifts and the mass of H-dibaryon in the flavor SU(3) limit are extracted from the resultant potentials by solving the Schrödinger equation. The NN phase-shifts in the SU(3) limit is shown to have qualitatively similar behavior as the experimental data. A bound H-dibaryon in the SU(3) limit is found to exist in the flavor-singlet JP=0+ channel with the binding energy of about 26 MeV for the lightest quark mass Mps=469 MeV. Effect of flavor SU(3) symmetry breaking on the H-dibaryon is estimated by solving the coupled-channel Schrödinger equation for ΛΛ–NΞ–ΣΣ with the physical baryon masses and the potential matrix obtained in the SU(3) limit: a resonant H-dibaryon is found between ΛΛ and NΞ thresholds in this treatment.
Imaginary-time Nambu–Bethe–Salpeter (NBS) wave function is introduced to extend our previous approach for hadron–hadron interactions on the lattice. Scattering states of hadrons with different ...energies encoded in the NBS wave function are utilized to extract non-local hadron–hadron potential. “The ground state saturation”, which is commonly used in lattice QCD but is hard to be achieved for multi-baryons, is not required. We demonstrate that the present method works efficiently for the nucleon–nucleon interaction (the potential and the phase shift) in the S01 channel.
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