Influence of the vector interaction and an external magnetic field on the isentropes near the chiral critical end point

TL;DR

This paper investigates how vector interactions and magnetic fields influence the behavior of isentropic trajectories near the QCD critical end point using the (2+1) Nambu-Jona-Lasinio model with Polyakov loop coupling.

Contribution

It provides a detailed analysis of the effects of magnetic fields and vector interactions on the QCD phase diagram and isentropic trajectories near the CEP, considering different physical scenarios.

Findings

Vector interaction weakens the first-order transition and smooths isentropes.

Strong magnetic fields strengthen the first-order transition and shift isentropes to higher temperatures.

No focusing of isentropes towards the CEP was observed.

Abstract

The location of the critical end point (CEP) and the isentropic trajectories in the QCD phase diagram are investigated. We use the (2+1) Nambu$-$Jona-Lasinio model with the Polyakov loop coupling for different scenarios, namely by imposing zero strange quark density, which is the case in the ultra relativistic heavy-ion collisions, and $\beta$-equilibrium. The influence of strong magnetic fields and of the vector interaction on the isentropic trajectories around the CEP is discussed. It is shown that the vector interaction and the magnetic field, having opposite effects on the first-order transition, affect the isentropic trajectories differently: as the vector interaction increases, the first-order transition becomes weaker and the isentropes become smoother; when a strong magnetic field is considered, the first-order transition is strengthened and the isentropes are pushed to higher temperatures. No focusing of isentropes in region towards the CEP is seen.