Khin Swe Myint

Lambda Lambda - Xi N coupling effects in light hypernuclei

Abstract:The significance of ΛΛ-Ξ N coupling in double-Λ hypernuclei has been studied. The Pauli suppression effect due to this coupling in 6ΛΛ He has been found to be 0.43MeV for the coupling strength of the NSC97e potential. This indicates that the free-space ΛΛ interaction is stronger by an about 5° phase shift than that deduced from the empirical data of 6ΛΛ He without including the Pauli suppression effect. In 5ΛΛ He and 5ΛΛ H, an attractive term arising from the ΛΛ-Ξ N conversion is enhanced by the formation of an alpha-particle in the intermediate Ξ states. According to this enhancement, we have found that the ΛΛ binding energy ( ΔBΛΛ) of 5ΛΛ He is about 0.27MeV larger than that of 6ΛΛ He for the NSC97e coupling strength. This finding deviates from the general picture that the heavier is the core nucleus, the larger is ΔBΛΛ.-1

ΛNN Three‐Body Force due to Coherent Λ‐Σ Coupling

The overbinding problem of Λ5He is solved by introducing a concept of coherent Λ‐Σ coupling which is equivalent to a ΛNN three‐body force. This three‐body force is coherently enhanced in the 0+ states of Λ4H and Λ4He. The 0+−1+ splitting in these hypernuclei is mainly due to coherent Λ‐Σ coupling and partly due to the ΛN spin‐spin interaction. A ΛNN three‐body potential is derived from the coupled‐channel treatment. The origin of the repulsive and attractive nature of the three‐body force is discussed. Coherent Λ‐Σ coupling becomes more important in neutron‐rich hypernuclei and especially in neutron‐star matter at high densities. The possible existence of “hyperheavy hydrogen”, Λ6H, is suggested.

HYPERONS IN HIGH-DENSITY NUCLEAR MEDIUM: IS Λ-Σ0 MIXING LARGE OR SMALL?

The Λ-Σ0 mixing in neutron star matter is discussed in three theoretical models: the G-matrix theory, the relativistic mean field theory and the QCD sum-rule approach. The mixing of 2~8% at the critical baryon density of Λ appearance(2.3 times of the normal nuclear density) is predicted in the G-matrix theory. The second and third models give smaller mixing, 0.2~1.0% and < 0.25%, respectively. Since the G-matrix theory is the most dynamical model among the three, the mixing of 2~10% at 2~3 times of the normal density may be realistic.

Kaonic nuclear systems K̄N and K̄NN as decaying states

The formation spectra of model K̄N and K̄NN systems formed by (K−, n) reactions are investigated in order to obtain a theoretical basis for a proper interpretation of experimental data concerning kaonic nuclear quasi-bound states. It has been clarified that the experimentally observable kaonic nuclear state K−pp should be regarded as the decaying state introduced by Kapur-Peierls, which is different from the pole state solution of the Faddeev equation.