Constraining Nuclear Symmetry Energy from Converting Neutron Star EoS into HI Collisions

The symmetry energy expansion is important for connecting nuclear experiments to neutron stars. However, the expansion coefficients have significant error bars. In our study, we take the symmetry energy expansion with 4 coefficients and focus specifically on the possibility that neutron stars may have a large bump in the speed of sound, motivated by the observation of heavy neutron stars.

A natural question is whether this behavior is compatible with heavy-ion experimental data. We explore the entire range allowed by the experimentally obtained coefficients to produce a prior distribution for the speed of sound functional using charge constraints compatible with heavy-ion experiments. Only a fraction of the resulting equations of state are causal and stable. By imposing stability and causality, we find in the posterior distribution that a large bump in the speed of sound can further constrain the symmetry energy expansion coefficients.