Nuclear Symmetry Energy with Strangeness in Heavy Ion Collision

Abstract

The role of anti-kaons in the symmetry energy to be determined in heavy-ion collisions as for instance in such observables as the $\pi^-/\pi^+$ ratio is discussed using a simple chiral Lagrangian. It is shown, with some mild assumptions, that kaons, when present in the system, can affect the EoS appreciably for both symmetric and asymmetric nuclear matter. For nuclear matter with small asymmetry with which heavy-ion collisions are studied, it may be difficult to distinguish a stiff symmetry energy and the supersoft symmetry energy, even with kaons present. However the effect of kaon is found to be significant such that $\mu_n-\mu_p \neq 0$ near $x=1/2$, at which the chemical potential difference is zero without kaon amplitude. We present the argument that in order to obtain a reliably accurate equation of state (EoS) for compact-star matter, a much deeper understanding is needed on how the strangeness degrees of freedom such as kaons, hyperons etc. behave in baryonic matter in a Fermi liquid (or possibly a non-Fermi liquid) phase with potential phase changes. It is suggested that such an {\em accurate} treatment could have an important implication on possibly modified gravity.