Influence of the inverse magnetic catalysis and the vector interaction in the location of the critical end point

Abstract

The effect of a strong magnetic field on the location of the critical end point (CEP) in the QCD phase diagram is discussed under different scenarios. In particular, we consider the contribution of the vector interaction and take into account the inverse magnetic catalysis obtained in lattice QCD calculations at zero chemical potential. The discussion is realized within the (2 þ 1) Polyakov-Nambu-Jona-Lasinio model. It is shown that the vector interaction and the magnetic field have opposite competing effects, and that the winning effect depends strongly on the intensity of the magnetic field. The inverse magnetic catalysis at zero chemical potential has two distinct effects for magnetic fields above ≳0.3 GeV 2 : it shifts the CEP to lower chemical potentials, hinders the increase of the CEP temperature and prevents a too large increase of the baryonic density at the CEP. For fields eB < 0.1 GeV 2 the competing effects between the vector contribution and the magnetic field can move the CEP to regions of temperature and density in the phase diagram that could be more easily accessible to experiments.

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

“…[27,29,46]. The main conclusions when μ u ¼ μ d ¼ μ s were that the trend is similar for both models: as the intensity of the magnetic field increases until a certain value (eB ∼ 0.4 GeV 2 [27,29]), the transition temperature increases and the baryonic chemical potential decreases. For even stronger magnetic fields, when no inverse magnetic catalysis (IMC) effects are considered, both T CEP and μ CEP B increase [27,46].…”

“…[28] and more recently in Ref. [29], where the presence of an external magnetic field was also considered. It was shown that the CEP can be absent in the phase diagram when the value of the coupling G V is greater than the critical value of G crit V ≈ 0.71G S within the present parametrization [29].…”

“…[29], where the presence of an external magnetic field was also considered. It was shown that the CEP can be absent in the phase diagram when the value of the coupling G V is greater than the critical value of G crit V ≈ 0.71G S within the present parametrization [29]. Indeed, as the value of G V is increased from 0 to G crit V , the first-order phase transition is weakened: the CEP is located at lower temperatures and larger chemical potentials, but smaller densities.…”

“…When IMC effects [47,48] are taken into account, noticeable effects on the location of the CEP occur for sufficiently high values of the magnetic field: the CEP will now occur at increasingly smaller chemical potentials and at a practically unchanged temperature [29]. Under an increase of the magnetic field, the CEP eventually moves toward μ B ¼ 0, and the deconfinement and chiral phase transitions should become of first order as predicted by lattice calculations [49].…”

“…It is also important to point out that the location of the CEP is affected by several conditions like the isospin or strangeness content of the medium [27], the role of the vector interaction in the medium [28,29] or the presence of an external magnetic field [27,29]. The possible location of the CEP will allow us to set stricter constraints on effective models.…”