Speaker
Description
Light nuclear clusters, such as H and He isotopes, are expected to be present in astrophysical environments and play an important role in different astrophysical phenomena involving ultra-dense baryonic matter: in binary neutron star mergers, the abundance of light clusters has a direct influence on the fraction of the ejecta, or on the viscous evolution of the accretion disk after the merger. However, the estimation of their abundance demands to correctly estimate the in-medium modification of their binding energy. This can be achieved in a phenomenological way, if theoretical models are calibrated to experimental data from heavy-ion collisions (HIC), where these same clusters are produced in comparable density and temperature conditions.
Useful observables to pin down the light nuclei effects with the medium have been extracted from HIC by the NIMROD and the INDRA collaborations. Recently, the INDRA data has been used to constraint a phenomenological model using Bayesian inference.
In this talk, we will address the low-density equation of state with the inclusion of light clusters. We will consider not only from the theoretical point of view how these light clusters are calculated for warm nuclear matter in the framework of relativistic mean-field models with in-medium effects, but also how these models were calibrated to experimental data from heavy-ion collisions, measured by the INDRA Collaboration. The in-medium effects are included in a two-fold way: via the couplings of the clusters to the mesons, that were calibrated to the experimental data, and via a binding energy shift.
We will also analyze the effect of including an exotic state state, the tetraneutron, that was reported in Duer et al, Nature 606, 678 (2022) as a resonant state, on the yields of the other light clusters. We calculate the abundances of the light clusters and chemical equilibrium constants with and without this exotic cluster. We also analyze how the associated energy of the tetraneutron would influence such results.
We find that the low-temperature, neutron-rich systems are the ones most affected by the presence of the tetraneutron, making neutron stars excellent environments for their formation. Moreover, its presence in strongly asymmetric matter may increase the proton and $\alpha-$particle fractions considerably. This may have an influence on the dissolution of the accretion disk of the merger of two neutron stars.
