Juan Pablo Carlomagno

We investigate the thermodynamic properties of cold magnetized quark matter within a nonlocal Nambu–Jona-Lasinio model. Our study addresses the equation of state, anisotropic pressures, quark density, speed of sound, and magnetic susceptibility, with direct comparison to the chiral limit. Strong magnetic fields are found to generate marked anisotropy; the longitudinal pressure and speed of sound are enhanced, approaching the causal bound in the lowest Landau-level regime, while the transverse components are systematically reduced. The quark density exhibits magnetic catalysis, increasing with both the chemical potential and the magnetic field strength. At moderate to high fields, the critical chemical potential decreases with increasing e B , signaling the occurrence of inverse magnetic catalysis at finite chemical potential. Magnetic susceptibility displays oscillations around zero in low fields, driven by de Haas–van Alphen-like effects, and settles at positive values for strong fields, consistent with an overall growth of magnetization. Compared with the chiral limit, the inclusion of finite current quark masses does not modify the overall oscillatory behavior, but changes the nature of the Landau-level transitions, which become weakly first order instead of second order.

We analyze the topological susceptibility and the axion properties in the presence of an external uniform magnetic field, considering a three-flavor Nambu-Jona-Lasinio model that includes strong C P violation through a ’t Hooft-like flavor mixing term. Both thermal and finite density effects are studied for magnetic fields up to 1 GeV 2 , and the corresponding phase transitions are analyzed. To capture the inverse magnetic catalysis effect at finite temperatures and densities, a magnetic-field-dependent coupling constant is considered. Our analytical and numerical results are compared with those previously obtained from lattice QCD, chiral perturbation theory, and other effective models.

We analyze the topological susceptibility and the axion properties in the presence of an external uniform magnetic field, considering a three flavor NJL model that includes strong CP violation through a 't Hooft-like flavor mixing term. Both thermal and finite density effects are studied for magnetic fields up to 1 GeV$^2$, and the corresponding phase transitions are analyzed. To capture the inverse magnetic catalysis effect at finite temperatures and densities, a magnetic field-dependent coupling constant is considered. Our analytical and numerical results are compared with those previously obtained from lattice QCD, chiral perturbation theory and other effective models.

We present a study of hybrid neutron stars with color superconducting quark matter cores at finite temperature that results in sequences of stars with constant entropy per baryon, s/nB=const. For the quark matter equation of state, we employ a recently developed nonlocal chiral quark model while nuclear matter is described with a relativistic density functional model of the DD2 class. The phase transition is obtained by a Maxwell construction under isothermal conditions. We find that traversing the mixed phase on a trajectory at low s/nB≲2 in the phase diagram shows a heating effect while at larger s/nB the temperature drops. This behavior may be attributed to the presence of a color superconducting quark matter phase at low temperatures and the melting of the diquark condensate which restores the normal quark matter phase at higher temperatures. While the isentropic hybrid star branch at low s/nB≲2 is connected to the neutron star branch, it gets disconnected at higher entropy per baryon so that the "thermal twin" phenomenon is observed. We find that the transition from connected to disconnected hybrid star sequences may be estimated with the Seidov criterion for the difference in energy densities. The radii and masses at the onset of deconfinement exhibit a linear relationship and thus define a critical compactness of the isentropic star configuration for which the transition occurs which for large enough s/nB≳2 is accompanied by an instability. The results of this study may be of relevance for uncovering the conditions for the supernova explodability of massive blue supergiant stars by the quark deconfinement mechanism. The accretion-induced deconfinement transition with thermal twin formation may contribute to explaining the origin of eccentric orbits in some binary systems and the origin of isolated millisecond pulsars.

We study the features of low energy strong interactions for a system at zero temperature and finite baryon and isospin chemical potentials, in the framework of a Nambu–Jona-Lasinio-like model that includes nonlocal four-point interactions. We analyze the phase transitions corresponding to chiral symmetry restoration and pion condensation, comparing our results with those obtained from local NJL-like models and lattice QCD calculations. Published by the American Physical Society 2024

We investigate the extension to finite temperatures and neutrino chemical potentials of a recently developed nonlocal chiral quark model approach to the equation of state of neutron star matter. We consider two light quark flavors and current-current interactions in the scalar-pseudoscalar, vector, and diquark pairing channels, where the nonlocality of the currents is taken into account by a Gaussian form factor that depends on the spatial components of the 4-momentum. Within this framework, we analyze order parameters, critical temperatures, phase diagrams, equations of state, and mass-radius relations for different temperatures and neutrino chemical potentials. For parameters of the model that are constrained by recent multimessenger observations of neutron stars, we find that the mass-radius diagram for isothermal hybrid star sequences exhibits the thermal twin phenomenon for temperatures above 30 MeV.

We study the features of low energy strong interactions for a system at zero temperature and finite baryon and isospin chemical potentials, in the framework of a Nambu--Jona-Lasinio-like model that includes nonlocal four-point interactions. We analyze the phase transitions corresponding to chiral symmetry restoration and pion condensation, comparing our results with those obtained from local NJL-like models and lattice QCD calculations.