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Ricardo L. S. Farias

Publications and source records attributed to Ricardo L. S. Farias.

48 records · Page 3Linked to original sources

Deconfinement and chiral phase transitions in quark matter with a strong electric field

The deconfinement and chiral phase transitions are studied in the context of the electrized quark matter at finite temperature in the two-flavor Polyakov-Nambu--Jona-Lasinio model. Using the mean field approximation and an electric field independet regularization we show that the effect of temperature and/or electric fields is to partially restore the chiral symmetry. The deconfinement phase transition is slightly affected by the magnitude of the electric field. To this end we show how the effective quark masses and the expectation value of the Polyakov Loop are affected by the electric fields at finite temperatures. As a very interesting result, the pseudocritical temperatures for chiral symmetry restoration and deconfinement decrease as we increase the magnitude of the electric fields, however, both start to increase after some critical value of the electric field.

hep-ph↗

Cold QCD at finite isospin density: confronting effective models with recent lattice data

We compute the QCD equation of state for zero temperature and finite isospin density within the Nambu-Jona-Lasinio model in the mean field approximation, motivated by the recently obtained Lattice QCD results for a new class of compact stars: pion stars. We have considered both the commonly used Traditional cutoff Regularization Scheme and the Medium Separation Scheme, where in the latter purely vacuum contributions are separated in such a way that one is left with ultraviolet divergent momentum integrals depending only on vacuum quantities. We have also compared our results with the recent results from Lattice QCD and Chiral Perturbation Theory.

hep-ph↗

Quantum chromodynamics axion in a hot and magnetized medium

It is analyzed the effects of a hot and magnetized medium on the axion mass, self-coupling and topological susceptibility when in presence of an anisotropic external magnetic field along the $z$-direction, within the Nambu--Jona-Lasinio effective model for quantum chromodynamics. The effects of both Magnetic Catalysis and Inverse Magnetic Catalysis are explicitly taken into account through appropriate matching of parameters with those from lattice Monte-Carlo numerical simulations. It is also analyzed the dependence of the results with respect to different model parametrizations in the context of the Nambu--Jona-Lasinio model.

hep-ph↗

Neutral meson properties in hot and magnetized quark matter: a new magnetic field independent regularization scheme applied to NJL-type model

A magnetic field independent regularization scheme (zMFIR) based on the Hurwitz-Riemann zeta function is introduced. The new technique is applied to the regularization of the mean-field thermodynamic potential and mass gap equation within the SU(2) Nambu-Jona-Lasinio model in a hot and magnetized medium. The equivalence of the new and the standard MFIR scheme is demonstrated. The neutral meson pole mass is calculated in a hot and magnetized medium and the advantages of using the new regularization scheme are shown.

hep-ph↗

NJL-type models in the presence of intense magnetic fields: the role of the regularization prescription

We study the regularization dependence of the Nambu-Jona--Lasinio model (NJL) predictions for some properties of magnetized quark matter at zero temperature (and baryonic density) in the mean field approximation. The model parameter dependence for each regularization procedure is also analyzed in detail. We calculate the average and difference of the quark condensates using different regularization methods and compare with recent lattice results. In this context, the reliability of the different regularization procedures is discussed.

hep-ph↗

Regularization issues for a cold and dense quark matter model in $β-$equilibrium

A regularization scheme that explicitly separates vacuum contributions from medium effects is applied to a Nambu--Jona-Lasinio model with diquark interactions and in $β-$equilibrium. We perform a comparison of this proposed scheme with the more traditional one, where no separation of vacuum and medium effects is done. Our results point to both qualitative and quantitative important differences between these two methods, in special regarding the phase structure of the model in the cold and dense nuclear matter case.

hep-ph↗

Effect of the magnetized medium on the decay of neutral scalar bosons

The decay of a heavy neutral scalar particle into fermions and into charged scalars are analyzed when in the presence of an external magnetic field and finite temperature. Working in the one-loop approximation for the study of these decay channels, it is shown that the magnetic field leads in general to a suppression of the decay width whenever the kinematic constrain depends explicitly on the magnetic field. Our results are also compared with common approximations found in the literature, e.g., when the magnitude of the external magnetic field is smaller than the decaying product particle masses, i.e., in the weak field approximation, and in the opposite case, i.e., in the strong field approximation. Possible applications of our results are discussed.

hep-ph↗

Magnetic field-dependence of the neutral pion mass in the linear sigma model coupled to quarks: The weak field case

We compute the neutral pion mass dependence on a magnetic field in the weak field approximation at one-loop order. The calculation is carried out within the linear sigma model coupled to quarks and using Schwinger's proper-time representation for the charged particle propagators. We find that the neutral pion mass decreases with the field strength provided the boson self-coupling magnetic field corrections are also included. The calculation should be regarded as the setting of the trend for the neutral pion mass as the magnetic field is turned on.

hep-ph↗

Anisotropy in the equation of state of strongly magnetized quark matter within the Nambu--Jona-Lasinio Model

In this article, we calculate the magnetization and other thermodynamical quantities for strongly magnetized quark matter within the Nambu-Jona-Lasinio model at zero temperature. We assume two scenarios, chemically equilibrated charge neutral matter present in the interior of compact stars and zero-strangeness isospin-symmetric matter created in nuclear experiments. We show that the magnetization oscillates with density but in a much more smooth form than what was previously shown in the literature. As a consequence, we do not see the unphysical behavior in the pressure in the direction perpendicular to the magnetic field that was previously found. Finally, we also analyze the effects of a vector interaction on our results.

hep-ph↗

$π_0$ pole mass calculation in a strong magnetic field and lattice constraints

The $π_0$ neutral meson pole mass is calculated in a strongly magnetized medium using the SU(2) Nambu-Jona-Lasinio model within the random phase approximation (RPA) at zero temperature and zero baryonic density. We employ a magnetic field dependent coupling, $G(eB)$, fitted to reproduce lattice QCD results for the quark condensates. Divergent quantities are handled with a magnetic field independent regularization scheme in order to avoid unphysical oscillations. A comparison between the running and the fixed couplings reveals that the former produces results much closer to the predictions from recent lattice calculations. In particular, we find that the $π_0$ meson mass systematically decreases when the magnetic field increases while the scalar mass remains almost constant. We also investigate how the magnetic background influences other mesonic properties such as $f_{π_0}$ and $g_{π_0 q q}$.

hep-ph↗

Superconducting and excitonic quantum phase transitions in doped systems with Dirac electrons

Material systems with Dirac electrons on a bipartite planar lattice and possessing superconducting and excitonic interactions are investigated both in the half-filling and doped regimes at zero temperature. Excitonic pairing is the analog of chiral symmetry breaking of relativistic fermion theories and produces an insulating gap in the electronic spectrum. Condensed matter systems with such competing interactions display phenomena that are analogous to the onset of the chiral condensate and of color superconductivity in dense quark matter. Evaluation of the free-energy (effective potential) allows us to map the phases of the system for different values of the couplings of each interaction. At half-filling, we show that Cooper pairs and excitons can coexist if the superconducting and excitonic interactions strengths are equal and above a quantum critical point, which is evaluated. If one of the interactions is stronger than the other, then only the corresponding order parameter is non-vanishing and we do not have coexistence. For nonzero values of chemical potential, the phase diagram for each interaction is obtained independently. Taking into account only the excitonic interaction, a critical chemical potential, as a function of the interaction strength, is obtained. If only the superconducting interaction is considered, the superconducting gap displays a characteristic dome as charge carriers are doped into the system and our results qualitatively reproduce the superconducting phase diagram of several compounds, like 122 pnictides and cuprate superconductors. We also analyze the possibility of coexistence between Cooper pairs and excitons and we show that, even if the excitonic interaction strength is greater than the superconducting interaction, as the chemical potential increases, superconductivity tends to suppress the excitonic order parameter.

cond-mat.mes-hall↗