$\Lambda^{\ast}(1405)$-matter: stable or unstable?

Abstract

A recent suggestion [PLB 774 (2017) 522] that purely-$\Lambda^{\ast}(1405)$ nuclei provide the absolute minimum energy in charge-neutral baryon matter for baryon-number $A\gtrsim 8$, is tested within RMF calculations. A broad range of $\Lambda^{\ast}$ interaction strengths, commensurate with $(\bar K \bar K NN)_{I=0}$ binding energy assumed to be of order 100 MeV, is scanned. It is found that the binding energy per $\Lambda^{\ast}$, $B/A$, saturates for $A\gtrsim 120$ with values of $B/A$ considerably below 100 MeV, implying that $\Lambda^{\ast}(1405)$ matter is highly unstable against strong decay to $\Lambda$ and $\Sigma$ hyperon aggregates. The central density of $\Lambda^{\ast}$ matter is found to saturate as well, at roughly twice nuclear matter density. Moreover, it is shown that the underlying very strong $\bar K N$ potentials, fitted for isospin $I=0$ to the mass and width values of $\Lambda^{\ast}(1405)$, fail to reproduce values of single-nucleon absorption fractions deduced across the periodic table from $K^-$ capture-at-rest bubble chamber experiments.