Λ^⁎(1405)-matter: Stable or unstable?

A recent suggestion by Akaishi and Yamazaki (2017) [3] that purely-Λ^⁎(1405) nuclei provide the absolute minimum energy in charge-neutral baryon matter for baryon-number A≳8, is tested within RMF calculations. A broad range of Λ^⁎ interaction strengths, commensurate with (K¯K¯NN)_I=0 binding energy assumed to be of order 100 MeV, is scanned. It is found that the binding energy per Λ^⁎, B/A, saturates for A≳120 with values of B/A considerably below 100 MeV, implying that Λ^⁎(1405) matter is highly unstable against strong decay to Λ and Σ hyperon aggregates. The central density of Λ^⁎ matter is found to saturate as well, at roughly twice nuclear matter density. Moreover, it is shown that the underlying very strong K¯N potentials, fitted for isospin I=0 to the mass and width values of Λ^⁎(1405), fail to reproduce values of single-nucleon absorption fractions deduced across the periodic table from K⁻ capture-at-rest bubble chamber experiments.