A 4D $T^\prime$-expanded lattice QCD equation of state with a multi-dimensional 3D-Ising-type critical contribution

Abstract

Inferring the possible existence and location of a critical point on the QCD phase diagram through experimental observations requires equations of state that include both lattice QCD constraints and critical behavior. In this manuscript, we present the first four-dimensional equation of state in the $(T,\mu_B,\mu_Q,\mu_S)$ space combining the lattice 4D $T^\prime$-Expansion Scheme with a critical contribution mapped from the 3D Ising model. We extend the earlier two-dimensional construction, the so-called Ising 2D-TExS in the $(T, \mu_B)$ plane, promoting the critical point to a parametrizable critical surface in the full four-dimensional thermodynamic space. Our framework provides a family of equations of state to systematically study the effects of criticality in realistic hydrodynamic simulations with $BQS$ conserved charges, going beyond the case of strangeness neutrality, by varying the geometry of the critical surface and the strength of criticality at finite $\mu_B$, $\mu_Q$ and $\mu_S$ separately.