arXiv subjects

J. P. Carlomagno

Publications and source records attributed to J. P. Carlomagno.

At least 19 recordsLinked to original sources

arXiv2026

Phase structure of magnetized quark matter at imaginary chemical potential

We investigate the phase structure of magnetized quark matter within a nonlocal SU(2) Polyakov-Nambu-Jona-Lasinio model. Our work focuses on the interplay between temperature and imaginary chemical potential in the presence of an external uniform magnetic field, with emphasis on the deconfinement and Roberge-Weiss transitions. We analyze the dependence of the relevant critical temperatures on the external field, and we explore the sensitivity of the phase structure to different Polyakov loop effective potentials. Our results show qualitative agreement with lattice QCD findings, reproducing inverse magnetic catalysis in the chiral sector and a decreasing behavior of the Roberge-Weiss transition temperature with increasing magnetic field.

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arXiv2025

Exploring Anisotropic Effects in Magnetized Quark Matter

We investigate the thermodynamic properties of cold magnetized quark matter within a nonlocal Nambu Jona Lasinio (nlNJL) 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 (LLL) 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 $eB$, signaling the occurrence of inverse magnetic catalysis at finite chemical potential ($μ$IMC). 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.

hep-ph↗

arXiv2025

Anisotropy in Magnetized Quark Matter in the Chiral Limit

We investigate the behavior of cold quark matter under strong magnetic fields in the frame of a nonlocal NJL model in the chiral limit. Our analysis focuses on deconfinement, chiral symmetry restoration, and the anisotropy in pressure induced by the external magnetic field. For $eB\lesssim 0.07~ \text{GeV}^2$, the critical chemical potential remains largely insensitive to the magnetic field, whereas at higher field strengths, transitions to chirally restored phases occur at progressively lower chemical potentials. The parallel and perpendicular pressures, respect to the magnetic field, exhibit distinct behaviors, reflecting the anisotropic nature of the system. Oscillations in the quark number density, driven by the de Haas van Alphen effect, reflect the quantized behavior of quarks in a magnetic field. Similarly, the magnetization displays oscillatory behavior, driven by the sequential filling of Landau levels. At lower external magnetic field strengths, contributions from orbital angular momentum and the population of higher Landau levels further modulate these oscillations. These results provide deeper insights into the thermodynamic and magnetic properties of quark matter under strong magnetic fields, with implications for astrophysical studies.

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arXiv2025

Topological susceptibility and axion properties in the presence of a strong magnetic field within the three-flavor NJL model

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.

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arXiv2024

Thermal twin stars within a hybrid equation of state based on a nonlocal chiral quark model compatible with modern astrophysical observations

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 multi-messenger 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.

nucl-th↗

arXiv2024

Cold isospin asymmetric baryonic rich matter in nonlocal NJL-like models

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.

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arXiv2023

$T {-} μ$ quark matter phase transitions and critical end point in nonlocal PNJL models

We study the $T {-} μ$ phase diagram of quark matter under the influence of a strong uniform magnetic field in the framework of a nonlocal extension of the Polyakov Nambu Jona Lasinio model (PNJL). The existence of a critical end point (CEP) is found for the whole considered range of the magnetic field (up to 1 $GeV^{2}$). We analyze the location of this CEP as a function of the external field and discuss the presence of inverse magnetic catalysis for nonzero chemical potentials. Our results show that the temperature of the CEP decreases with the magnetic field, in contrast to the behavior observed in local NJL/PNJL models.

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arXiv2022

Quark matter phase diagram under the influence of strong magnetic fields with a nonlocal chiral model

We study the phase diagram in the $T-μ$ plane for quark matter under the influence of a strong uniform magnetic field $\vec{B}$, in the framework of a non-local extension of the two-flavor Polyakov Nambu-Jona-Lasinio model. We analyze the deconfinement and chiral symmetry restoration transitions in the mean field approximation. For the considered parameterization, it is found that there is always a critical end point (CEP) in the $T-μ$ plane that separates a first-order transition line from a smooth crossover. The location of the CEP is studied as a function of the magnetic field.

hep-ph↗

arXiv2022

Charged pseudoscalar and vector meson masses under strong magnetic fields in an extended NJL model

The mass spectrum of $π^+$ and $ρ^+$ mesons in the presence of a static uniform magnetic field $\vec B$ is studied within a two-flavor NJL-like model. We improve previous calculations taking into account the effect of Schwinger phases carried by quark propagators, and using an expansion of meson fields in terms of the solutions of the corresponding equations of motion for nonzero $B$. It is shown that the meson polarization functions are diagonal in this basis. Our numerical results for the $ρ^+$ meson spectrum are found to disfavor the existence of a meson condensate induced by the magnetic field. In the case of the $π^+$ meson, $π$ - $ρ$ mixing effects are analyzed for the meson lowest energy state. The predictions of the model are compared with available lattice QCD results.

hep-ph↗

arXiv2022

Neutral pseudoscalar and vector meson masses under strong magnetic fields in an extended NJL model: mixing effects

Mixing effects on the mass spectrum of light neutral pseudoscalar and vector mesons in the presence of an external uniform magnetic field $\vec B$ are studied in the framework of a two-flavor NJL-like model. The model includes isoscalar and isovector couplings both in the scalar-pseudoscalar and vector sectors, and also incorporates flavor mixing through a 't Hooft-like term. Numerical results for the $B$ dependence of meson masses are compared with present lattice QCD results. In particular, it is shown that the mixing between pseudoscalar and vector meson states leads to a significant reduction of the mass of the lightest state. The role of chiral symmetry and the effect of the alignment of quark magnetic moments in the presence of the magnetic field are discussed.

hep-ph↗

arXiv2022

Quark-nuclear hybrid equation of state for neutron stars under modern observational constraints

We study a family of equations of state for hybrid neutron star matter. The hybrid EOS are obtained by a Maxwell construction of the first-order phase transition between a hadronic phase described by the relativistic density-functional EOS of the "DD2" class with excluded volume effects and a deconfined quark matter phase modeled by an instantaneous nonlocal version of the Nambu-Jona-Lasinio model in SU(2)$_f$ with vector interactions and color superconductivity. The form factor in the nonlocal quark matter model is fitted to lattice QCD results in the Coulomb gauge. Owing to strong coupling in the vector meson and diquark channels, a coexistence phase of color superconductivity and chiral symmetry breaking occurs. Our results show an approximately constant behavior for the squared speed of sound with values of 0.4 - 0.6 in the density region relevant for neutron star interiors. To simultaneously fulfill the constraints from the Neutron Star Interior Composition Explorer radius measurement for PSR J0740+6620 and tidal deformability from GW170817 it is necessary to consider a $μ$-dependent bag pressure that mimics confinement.

nucl-th↗

arXiv2021

Isospin asymmetric matter in a nonlocal chiral quark model

We analyze the features of strongly interacting matter in the presence of nonzero isospin chemical potential $μ_I$, within a nonlocal two-flavor Polyakov-Nambu-Jona-Lasinio (PNJL) model. For a system at finite temperature $T$, we describe the behavior of various thermodynamic quantities and study the phase diagram in the $μ_I - T$ plane. In particular, it is found that for values of $μ_I$ larger than the pion mass and temperatures lower than a critical value of about 170 MeV the system lies in an isospin symmetry broken phase signaled by the presence of a nonzero pion condensate. Our results for the phase diagram are found to be in better agreement with those arising from lattice QCD calculations, as compared to the predictions from other theoretical approaches like the local PNJL model.

hep-ph↗

arXiv2021

Strong-interaction matter under extreme conditions from chiral quark models with nonlocal separable interactions

We review the current status of the research on effective nonlocal NJL-like chiral quark models with separable interactions, focusing on the application of this approach to the description of the properties of hadronic and quark matter under extreme conditions. The analysis includes the predictions for various hadron properties in vacuum, as well as the study of the features of deconfinement and chiral restoration phase transitions for systems at finite temperature and/or density. We also address other related subjects, such as the study of phase transitions for imaginary chemical potentials, the possible existence of inhomogeneous phase regions, the presence of color superconductivity, the effects produced by strong external magnetic fields, and the application to the description of compact stellar objects.

hep-ph↗

arXiv2019

Relation between the continuum threshold and the Polyakov loop with the QCD deconfinement transition

Using vector and axial-vector correlators within finite energy sum rules with inputs from a chiral quark model, coupled to the Polyakov loop, with nonlocal vector interactions, we extend our previous work to confirm the equivalence between the continuum threshold $s_0$ and the trace of the Polyakov loop $Φ$ as order parameters for the deconfinement transition at finite temperature $T$ and quark chemical potential $μ$. The obtained results are in agreement with our initial conclusion, where we showed that $s_0(T,μ)$ and $Φ(T,μ)$ provide the same information for the QCD deconfinement transition.

hep-ph↗

arXiv2019

Vector and axial-vector meson properties in a nonlocal SU(2) PNJL model

We study the features of a SU(2) Polyakov-Nambu-Jona-Lasinio model that includes wave function renormalization and nonlocal vector interactions. Within this framework we analyze, among other properties, the masses, width and decay constants of light vector and axial-vector mesons at finite temperature. Then we obtain the corresponding phase diagram in a finite density scenario, after characterizing the deconfinement and chiral restoration transitions.

hep-ph↗

arXiv2018

Meson properties and phase diagrams in a SU(3) nlPNJL model with lQCD-inspired form factors

We study the features of a nonlocal SU(3) Polyakov-Nambu-Jona-Lasinio model that includes wave function renormalization. Model parameters are determined from vacuum phenomenology considering lattice QCD-inspired nonlocal form factors. Within this framework we analyze the properties of light scalar and pseudoscalar mesons at finite temperature and chemical potential determining characteristics of deconfinement and chiral restoration transitions.

hep-ph↗

arXiv2017

The continuum threshold and the Polyakov loop: A comparison between two deconfinement order parameters

We compare two order parameters for the deconfinement transition, induced by thermal and density effects, commonly used in the literature, namely the thermal and density evolution of the continuum threshold $s_{0}$, within the frame of the QCD sum rules, and the trace of the Polyakov loop $Φ$ in the framework of a nonlocal $SU(2)$ chiral quark model. We include in our discussion the evolution of the chiral quark condensate, the parameter that characterizes the chiral symmetry restoration. We found that essentially both order parameters, $s_{0}$ and $Φ$, provide the same information for the deconfinement transition, both for the zero and finite chemical potential cases. At zero density, the critical temperatures in both cases coincide exactly and, in the case of finite baryonic chemical potential $μ$, we find evidence for the appearance of a quarkyonic phase.

hep-ph↗

arXiv2017

Gluon condensate from the Polyakov loop

We estimate the temperature dependence of the gluon condensate from the Polyakov loop effective potential. It is presented how this analytic approach provides a simple picture for the electric gluon condensate around the deconfinement temperature, showing that it drops to zero in a temperature range which is in good agreement with different pure gauge lattice results.

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