Deeply bound dibaryon is incompatible with neutron stars and supernovae

We study the effect of a dibaryon $S$ in the mass range $1860<m_S<2054\mathrm{MeV}$, which is heavy enough not to disturb the stability of nuclei and light enough to possibly be cosmologically metastable. Such a deeply bound state can act as a baryon sink in regions of high baryon density and temperature. We find that the ambient conditions encountered inside a newly born neutron star are likely to sustain a sufficient population of hyperons to ensure that a population of $S$ dibaryons can equilibrate in less than a few seconds. This would be catastrophic for the stability of neutron stars and the observation of neutrino emission from the proto-neutron star of Supernova 1987A over $\sim \mathcal{O}(10)\mathrm{s}$. A deeply bound dibaryon is therefore incompatible with the observed supernova explosion, unless the cross section for $S$ production is severely suppressed.

Figure 1

(Left) Contours of $t_S$ as defined in Eq. (5) for $m_S=1900\mathrm{MeV}$ as a function of the $\mathrm{\Lambda }$ and $S$ sizes. The gray region violates Eq. (9) for $x=0$, 0.1. (Right) Contours of $t_S$ for $r_{\mathrm{\Lambda }}=0.76\mathrm{fm}$. In both panels, we have assumed $⟨{\sigma }_{N\mathrm{\Lambda }\to NN}v⟩=3\times {10}^{-30}{\mathrm{cm}}^3/\mathrm{s}$. The gray region violates Eq. (9) for $x=0$, 0.1. In the blue region, ${}^{16}\mathrm{O}$ nuclei are destabilized. In the purple region, the dibaryon has a singly weak decay. All of the parameter space depicted in each panel has $t_S\ll 10\mathrm{s}$ and is thus ruled out by the observation that SN1987A continued to emit neutrinos for $t_{\nu }\simeq 10\mathrm{s}$, unless $r_S$ is very close the minimum value allowed by Eq. (9).

Figure 2

(Left) The value of $⟨{\sigma }_{NN\to \mathrm{\Lambda }N}v⟩$ with and without phase-space degeneracy effects. (Right) The coupling $g_{\mathrm{\Lambda }S}^2$ from wave function overlap, as a function of $r_S$ for two different values of $r_{\mathrm{\Lambda }}$, as in Eq. (b1). In the gray region, $r_S$ violates Eq. (9) for $x=0.1$.