Speaker
Description
We investigate the zero-temperature equation of state at finite isospin density using the Nambu–Jona-Lasinio (NJL) model implemented within the Medium Separation Scheme (MSS), which cleanly separates medium effects from ultraviolet-divergent vacuum terms. Recent lattice QCD results reveal a nonmonotonic behavior of the speed of sound $c_s^2$ as a function of the isospin chemical potential $\mu_I$, with a clear violation of the conformal bound $c_s^2=1/3$. This unexpected feature, not predicted by conventional approaches — including standard NJL calculations — has drawn significant theoretical attention. We show that the NJL model, when consistently regularized via MSS, quantitatively reproduces state-of-the-art lattice data for isospin QCD, providing a natural explanation for the observed peak in $c_s^2$ and resolving artifacts typically associated with cutoff sensitivity in non renormalizable models.
