arXiv subjects

Efrain J. Ferrer

Publications and source records attributed to Efrain J. Ferrer.

At least 37 records · Page 2Linked to original sources

arXiv2011

Reply to comment on "Equation of state of dense and magnetized fermion system"

A Comment [1] to our recent article [2], expressed criticism on our estimate of the maximum magnetic field that can exist inside a neutron star and on the pressure anisotropy we found for a magnetized gas of fermions. These two points are relevant for the physics of neutron stars. With our reply we attempt not only to address the Comment's criticisms, but for the sake of the reader's understanding, we also try to clarify the connection between our and some literature's results mentioned in the comment.

astro-ph.SR↗

arXiv2011

Magnetic Tuning of the Relativistic BCS-BEC Crossover

The effect of an applied magnetic field in the crossover from Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) pairing regimes is investigated. We use a model of relativistic fermions and bosons inspired by those previously used in the context of cold fermionic atoms and in the magnetic-color-flavor-locking phase of color superconductivity. It turns out that as with cold atom systems, an applied magnetic field can also tune the BCS-BEC crossover in the relativistic case. We find that no matter what the initial state is at B=0, for large enough magnetic fields the system always settles into a pure BCS regime. In contrast to the atomic case, the magnetic field tuning of the crossover in the relativistic system is not connected to a Feshbach resonance, but to the relative numbers of Landau levels with either BEC or BCS type of dispersion relations that are occupied at each magnetic field strength.

nucl-th↗

arXiv2011

Cooper Pair's Magnetic Moment in MCFL Color Superconductivity

We investigate the effect of the alignment of the magnetic moments of Cooper pairs of charged quarks that form at high density in three-flavor quark matter. The high density phase of this matter in the presence of a magnetic field is known to be the Magnetic Color-Flavor-Locked (MCFL) phase of color superconductivity. We derive the Fierz identities of the theory and show how the explicit breaking of the rotational symmetry by the uniform magnetic field field opens new channels of interactions and allows the formation of a new diquark condensate. The new order parameter is a spin-1 diquark condensate proportional to the component in the field direction of the average magnetic moment of the pairs of charged quarks. In the region of large fields, the new condensate's magnitude becomes comparable to the larger of the two scalar gaps. Since there is no solution of the gap equations with nonzero scalar gaps and zero value of this magnetic moment condensate, its presence in the MCFL phase is unavoidable. This is consistent with the fact that the extra condensate does not break any symmetry that has not already been broken by the known MCFL gaps. The spin-1 condensate enhances the condensation energy of pairs formed by charged quarks and the magnetization of the system. We discuss the possible consequences of the new order parameter on the issue of the chromomagnetic instability that appears in color superconductivity at moderate density.

nucl-th↗

arXiv2011

Paraelectricity in Magnetized Massless QED

We show that the chiral-symmetry-broken phase of massless QED in the presence of a magnetic field exhibits strong paraelectricity. A large anisotropic electric susceptibility develops in the infrared region, where most of the fermions are confined to their lowest Landau level, and dynamical mass and anomalous magnetic moment are generated via the magnetic catalysis mechanism. The nonperturbative nature of this effect is reflected in the dependence of the electric susceptibility on the fine-structure constant. The strong paraelectricity is linked to the electric dipole moments of the particle/anti-particle pairs that form the chiral condensate. The significant electric susceptibility can be used as a probe to detect the realization of the magnetic catalysis of chiral symmetry breaking in physical systems.

hep-ph↗

arXiv2011

Equation of state for the MCFL phase and its implications for compact star models

Using the solutions of the gap equations of the magnetic-color-flavor-locked (MCFL) phase of paired quark matter in a magnetic field, and taking into consideration the separation between the longitudinal and transverse pressures due to the field-induced breaking of the spatial rotational symmetry, the equation of state (EoS) of the MCFL phase is self-consistently determined. This result is then used to investigate the possibility of absolute stability, which turns out to require a field-dependent bag constant to hold. That is, only if the bag constant varies with the magnetic field, there exists a window in the magnetic field vs. bag constant plane for absolute stability of strange matter. Implications for stellar models of magnetized (self-bound) strange stars and hybrid (MCFL core) stars are calculated and discussed.

astro-ph.HE↗

arXiv2010

Equation of State of a Dense and Magnetized Fermion System

The equation of state of a system of fermions in a uniform magnetic field is obtained in terms of the thermodynamic quantities of the theory by using functional methods. It is shown that the breaking of the O(3) rotational symmetry by the magnetic field results in a pressure anisotropy, which leads to the distinction between longitudinal- and transverse-to-the-field pressures. A criterion to find the threshold field at which the asymmetric regime becomes significant is discussed. This threshold magnetic field is shown to be the same as the one required for the pure field contribution to the energy and pressures to be of the same order as the matter contribution. A graphical representation of the field-dependent anisotropic equation of state of the fermion system is given. Estimates of the upper limit for the inner magnetic field in self-bound stars, as well as in gravitationally bound stars with inhomogeneous distributions of mass and magnetic fields, are also found.

hep-ph↗

arXiv2010

Abrikosov Gluon Vortices in Color Superconductors

In this talk I will discuss how the in-medium magnetic field can influence the gluon dynamics in a three-flavor color superconductor. It will be shown how at field strengths comparable to the charged gluon Meissner mass a new phase can be realized, giving rise to Abrikosov's vortices of charged gluons. In that phase, the inhomogeneous gluon condensate anti-screens the magnetic field due to the anomalous magnetic moment of these spin-1 particles. This paramagnetic effect can be of interest for astrophysics, since due to the gluon vortex antiscreening mechanism, compact stars with color superconducting cores could have larger magnetic fields than neutron stars made up entirely of nuclear matter. I will also discuss a second gluon condensation phenomenon connected to the Meissner instability attained at moderate densities by two-flavor color superconductors. In this situation, an inhomogeneous condensate of charged gluons emerges to remove the chromomagnetic instability created by the pairing mismatch, and as a consequence, the charged gluonic currents induce a magnetic field. Finally, I will point out a possible relation between glitches in neutron stars and the existence of the gluon vortices.

nucl-th↗

arXiv2010

Induced Magnetism in Color-Superconducting Media

The dense core of compact stars is the natural medium for the realization of color superconductivity. A common characteristic of such astrophysical objects is their strong magnetic fields, especially those of the so called magnetars. In this talk, I discuss how a color superconducting core can generate or/and enhance the stellar magnetic field independently of a magnetohydrodynamic dynamo mechanism. The magnetic field generator is in this case a gluonic current which circulates to stabilize the color superconductor in the presence of a strong magnetic field or under the pairing stress produced in the medium by the neutrality and $β$-equilibrium constraints.

hep-ph↗

arXiv2009

Dynamically Generated Anomalous Magnetic Moment in Massless QED

In this paper we investigate the non-perturbative generation of an anomalous magnetic moment for massless fermions in the presence of an external magnetic field. In the context of massless QED in a magnetic field, we prove that the phenomenon of magnetic catalysis of chiral symmetry breaking, which has been associated in the literature with dynamical mass generation, is also responsible for the generation of a dynamical anomalous magnetic moment. As a consequence, the degenerate energy of electrons in Landau levels higher than zero exhibits Zeeman splitting. We explicitly report the splitting for the first Landau level and find the non-perturbative Lande $\textit{g}$-factor and Bohr magneton. We anticipate that a dynamically generated anomalous magnetic moment will be a universal feature of theories with magnetic catalysis. Our findings can be important for condensed planar systems as graphene, as well as for highly magnetized dense systems as those forming the core of compact stars.

hep-ph↗

arXiv2008

Super-Dense Matter at Super- Strong Magnetic Fields

Our Universe is full of regions where extreme physical conditions are realized. A most intriguing case is the super-dense core of neutron stars, some of which also have super-strong magnetic fields, hence called magnetars. In this paper we review the current understanding of the physical properties of the different phases of quark matter at very high densities in the presence of large magnetic fields. We also discuss how the Meissner instability produced at moderate densities by a pairing stress due to the medium neutrality and $β$-equilibrium constraints can lead to the spontaneous generation of a magnetic field.

hep-ph↗

arXiv2008

Dynamically Induced Zeeman Effect in Massless QED

It is shown that in non-perturbative massless QED an anomalous magnetic moment is dynamically induced by an applied magnetic field. The induced magnetic moment produces a Zeeman splitting for electrons in Landau levels higher than $l=0$. The expressions for the non-perturbative Lande g-factor and Bohr magneton are obtained. Possible applications of this effect are outlined.

hep-ph↗

arXiv2007

Chromomagnetic Instability and Induced Magnetic Field in Neutral Two-Flavor Color Superconductivity

We find that the chromomagnetic instability existing in neutral two- flavor color superconductivity at moderate densities is removed by the formation of an inhomogeneous condensate of charged gluons and the corresponding induction of a magnetic field. It is shown that this inhomogeneous ground state is energetically favored over a homogeneous one. The spontaneous induction of a magnetic field in a color superconductor at moderate densities can be of interest for the astrophysics of compact stellar objects exhibiting strong magnetic fields as magnetars.

hep-ph↗

arXiv2007

Gluon Vortices and Induced Magnetic Field in Compact Stars

The natural candidates for the realization of color superconductivity are the extremely dense cores of compact stars, many of which have very large magnetic fields, especially the so-called magnetars. In this paper we discuss how a color superconducting core can serve to generate and enhance the stellar magnetic field without appealing to a magnetohydrodynamic dynamo mechanism.

astro-ph↗

arXiv2007

Magnetic Phases in Three-Flavor Color Superconductivity

The best natural candidates for the realization of color superconductivity are quark stars -not yet confirmed by observation- and the extremely dense cores of compact stars, many of which have very large magnetic fields. To reliably predict astrophysical signatures of color superconductivity, a better understanding of the role of the star's magnetic field in the color superconducting phase that realizes in the core is required. This paper is an initial step in that direction. The field scales at which the different magnetic phases of a color superconductor with three quark flavors can be realized are investigated. Coming from weak to strong fields, the system undergoes first a symmetry transmutation from a Color-Flavor-Locked (CFL) phase to a Magnetic-CFL (MCFL) phase, and then a phase transition from the MCFL phase to the Paramagnetic-CFL (PCFL) phase. The low-energy effective theory for the excitations of the diquark condensate in the presence of a magnetic field is derived using a covariant representation that takes into account all the Lorentz structures contributing at low energy. The field-induced masses of the charged mesons and the threshold field at which the CFL $\to$ MCFL symmetry transmutation occurs are obtained in the framework of this low-energy effective theory. The relevance of the different magnetic phases for the physics of compact stars is discussed.

nucl-th↗

arXiv2007

Paramagnetism in color superconductivity and compact stars

It is quite plausible that color superconductivity occurs in the inner regions of neutron stars. At the same time, it is known that strong magnetic fields exist in the interior of these compact objects. In this paper we discuss some important effects that can occur in the color superconducting core of compact stars due to the presence of the stars' magnetic field. In particular, we consider the modification of the gluon dynamics for a color superconductor with three massless quark flavors in the presence of an external magnetic field. We show that the long-range component of the external magnetic field that penetrates the color-flavor locked phase produces an instability for field values larger than the charged gluons' Meissner mass. As a consequence, the ground state is restructured forming a vortex state characterized by the condensation of charged gluons and the creation of magnetic flux tubes. In the vortex state the magnetic field outside the flux tubes is equal to the applied one, while inside the tubes its strength increases by an amount that depends on the amplitude of the gluon condensate. This paramagnetic behavior of the color superconductor can be relevant for the physics of compact stars.

astro-ph↗

arXiv2006

Magnetic Fields Boosted by Gluon Vortices in Color Superconductivity

We investigate the effects of an external magnetic field in the gluon dynamics of a color superconductor with three massless quark flavors. In the framework of gluon mean-field theory at asymptotic densities, we show that the long-range component $\widetilde{H}$ of the external magnetic field that penetrates the CFL phase produces an instability when its strength becomes larger than the Meissner mass of the charged gluons. As a consequence, the magnetic field causes the formation of a vortex state characterized by the condensation of charged gluons and the creation of magnetic flux tubes. Inside the flux tubes the magnetic field is stronger than the applied one. This antiscreening effect is connected to the anomalous magnetic moment of the gluon field. We suggest how this same mechanism could serve to remove the chromomagnetic instabilities existing in gapless color superconductivity.

hep-ph↗

arXiv2006

Color-Superconducting Gap in the Presence of a Magnetic Field

We explore the effects of an external magnetic field in the structure and magnitude of the diquark condensate in a three massless quark flavor color superconductor. It is shown that the long-range component $\widetilde{B}$ of the external magnetic field that penetrates the color-flavor locked (CFL) phase modifies its gap structure, producing a new phase of lower symmetry. Our analysis is performed within an NJL effective field theory with four-fermion interactions, inspired by one-gluon exchange. Using Ritus' method, we compute the quark propagators in the presence of a background magnetic field, and derive the gap equations for arbitrary values of the field. An analytical solution is found for strong magnetic fields. A main outcome of our study is that the $\widetilde{B}$ field tends to strengthen the gaps that get contributions from pairs of $\widetilde{Q}$-charged quarks. These gaps are enhanced through the field-dependent density of states of the $\widetilde{Q}$-charged quarks on the Fermi surface. Our considerations are relevant for the study of highly magnetized compact stars.

hep-ph↗

arXiv2006

Dense Quark Matter in a Magnetic Field

We explore the effects of an applied strong external magnetic field in the structure and magnitude of the color superconducting diquark condensate of a three massless flavor theory. The long-range component of the B field that penetrates the superconductor enhances the condensates formed by quarks charged with respect to this electromagnetic field.

hep-ph↗