arXiv subjects

D. Manreza Paret

Publications and source records attributed to D. Manreza Paret.

At least 19 recordsLinked to original sources

arXiv2024

Magnetized Strange Stars and Signals of Gravitational Waves

We study the emission of gravitational waves from spheroidal magnetized strange stars for both an isolated slowly rotating star and a binary system. In the first case, we compute the quadrupole moment and the amplitude of gravitational waves that may be emitted. For the binary system, the tidal deformability is obtained by solving simultaneously the system of spheroidal structure equations and the Love number equation. These results are compared with the data inferred from the GW170817 event which is also used to calculate the mass and tidal deformability of the companion star in the binary system. Our model supports binary systems formed by magnetized strange stars describing reasonable signals of gravitational waves contrasted with other models of binary systems composed of magnetized hadronic stars and non-magnetized quark stars.

gr-qc↗

arXiv2020

Thermal corrections to the gluon magnetic Debye mass

We compute the gluon polarization tensor in a thermo-magnetic environment in the strong magnetic field limit at zero and high temperature. The magnetic field effects are introduced using Schwinger's proper time method. Thermal effects are computed in the HTL approximation. At zero temperature, we reproduce the well-known result whereby for a non-vanishing quark mass, the polarization tensor reduces to the parallel structure and its coefficient develops an imaginary part corresponding to the threshold for quark-antiquark pair production. This coefficient is infrared finite and simplifies considerably when the quark mass vanishes. Keeping always the field strength as the largest energy scale, in the high temperature regime we analyze two complementary hierarchies of scales: $q^2\ll m_f^2\ll T^2$ and $m_f^2\ll q^2\ll T^2$. In the latter, we show that the polarization tensor is infrared finite as $m_f$ goes to zero. In the former, we discuss the thermal corrections to the magnetic Debye mass.

hep-ph↗

arXiv2019

Modeling anisotropic magnetized strange quark stars

Compact objects have an intrinsic anisotropy due to the presence of strong magnetic fields that cause considerable modifications on the equations of state (EoS). In this work, we study the impact of this anisotropy in the size and shape of magnetized strange quark stars using an axially symmetric metric in spherical coordinates, the gamma-metric. The results are compared with those obtained with the standard Tolman-Oppenheimer-Volkoff (TOV) equations for the parallel and perpendicular pressures independently. Differences in the results are discussed.

gr-qc↗

arXiv2019

Modeling anisotropic magnetized White Dwarfs with $γ$ metric

The effect of magnetic fields in the Equations of State (EoS) of compact objects is the splitting of the pressure in two components, one parallel and the other perpendicular to the magnetic field. This anisotropy suggests the necessity of using structure equations considering the axial symmetry of the magnetized system. In this work, we consider an axially symmetric metric in spherical coordinates, the $γ$-metric, and construct a system of equations to describe the structure of spheroidal compact objects. In addition, we connect the geometrical parameter $γ$ linked to the spheroid's radii, with the source of the anisotropy. So, the model relates the shape of the compact object to the physics that determines the properties of the composing matter. To illustrate how our structure equations work, we obtain the mass-radii solutions for magnetized White Dwarfs. Our results show that the main effect of the magnetic field anisotropy in White Dwarfs structure is to cause a deformation of these objects. Since this effect is only relevant at low densities, it does not affect the maximum values of magnetized White Dwarf's masses, which remain under Chandrasekhar limit.

astro-ph.HE↗

arXiv2018

(Self-)Magnetized Bose-Einstein Condensate stars

We study magnetic field effects on the Equations of State (EoS) and the structure of Bose-Einstein Condensate (BEC) stars, i.e. a compact object composed by a gas of interacting spin one bosons formed up by the pairing of two neutrons. To include the magnetic field in the thermodynamic description, we suppose that particle-magnetic field and particle-particle interactions are independent. We consider two configurations for the magnetic field: one where it constant and externally fixed, and another where it is produced by the bosons by self-magnetization. Since the magnetic field produces the splitting of pressures in the directions along and perpendicular to the magnetic axis, stable configurations of self-magnetized and magnetized BEC stars are studied using the recently found $γ$-structure equations that describe axially symmetric objects. The magnetized BEC stars are, in general spheroidal, less massive and smaller than the non-magnetic ones, being these effects more relevant at low densities. For the self-magnetized BEC stars their inner profiles of magnetic field can be computed as a function of the equatorial radii. The values obtained for the core and surface magnetic fields are in agreement with those typical of compact objects.

astro-ph.HE↗

arXiv2018

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↗

arXiv2018

Thermo-magnetic evolution of the QCD strong coupling

We study the one-loop gluon polarization tensor at zero and finite temperature in the presence of a magnetic field, to extract the thermo-magnetic evolution of the strong coupling $α_s$. We analyze four distinct regimes, to wit, the small and large field cases, both at zero and at high temperature. From a renormalization group analysis we show that at zero temperature, either for small or large magnetic fields, and for a fixed transferred momentum $Q^2$, $α_s$ grows with the field strength with respect to its vacuum value. However, at high temperature and also for a fixed value of $Q^2$ we find two different cases: When the magnetic field is even larger than the squared temperature, $α_s$ also grows with the field strength. On the contrary, when the squared temperature is larger than the magnetic field, a turnover behavior occurs and $α_s$ decreases with the field strength. This thermo-magnetic behavior of $α_s$ can help explain the inverse magnetic catalysis phenomenon found by lattice QCD calculations.

hep-ph↗

arXiv2018

Kicks of magnetized strange quark stars induced by anisotropic emission of neutrinos

We study the anisotropic neutrino emission from the core of neutron stars induced by the star's magnetic field. We model the core as made out of a magnetized ideal gas of strange quark matter and implement the conditions for stellar equilibrium in this environment. The calculation is performed without resorting to analytical simplifications and for temperature, density and magnetic field values corresponding to typical conditions for a neutron star's evolution. The anisotropic neutrino emission produces a rocket effect that contributes to the star's kick velocity. We find that the computed values for the kick velocity lie within the range of the observed values, reaching velocities of the order of $\sim1000$ km s$^{-1}$ for magnetic fields between $10^{15}-10^{18}$ G and radii of 20 to 5 km, respectively.

astro-ph.HE↗

arXiv2016

Constraints on the braneworld from compact stars

According to the braneworld idea, ordinary matter is confined on a 3-dimensional space (brane) that is embedded in a higher-dimensional space-time where gravity propagates. In this work, after reviewing the limits coming from general relativity, finiteness of pressure and causality on the brane, we derive observational constraints on the braneworld parameters from the existence of stable compact stars. The analysis is carried out by solving numerically the brane-modified Tolman-Oppenheimer-Volkoff equations, using different representative equations of state to describe matter in the star interior. The cases of normal dense matter, pure quark matter and hybrid matter are considered.

gr-qc↗

arXiv2016

Magnetized White Dwarfs

The purpose of this thesis is to obtain more realistic equations of state to describe the matter forming magnetized white dwarfs, and use them to solve its structure equations. The equations of state are determined by considering the weak magnetic field approximation $B<B_c$ ($B_c=4.41\times10^{13}\text{ G}$) for the electron gas of the star. The magnetic field introduces anisotropic pressures, even for the moderate values present in white dwarfs. Also, we consider the energy and pressure correction due to the Coulomb interaction of the electron gas with the ions located in a crystal lattice. Moreover, spherically symmetric Tolman-Oppenheimer-Volkoff structure equations are solved independently for the perpendicular and parallel pressures, confirming the necessity of using axisymmetric structure equations, more adequate to describe the anisotropic system. Therefore, we study the solutions in cylindrical coordinates. In this case, the mass per longitude unit is obtained instead of the total mass of the white dwarf.

astro-ph.HE↗

arXiv2015

(In-)Significance of the Anomalous Magnetic Moment of Charged Fermions for the Equation of State of a Magnetized and Dense Medium

We investigate the effects of the anomalous magnetic moment (AMM) in the equation of state (EoS) of a system of charged fermions at finite density in the presence of a magnetic field. In the region of strong magnetic fields (eB>m^2) the AMM is found from the one-loop fermion self-energy. In contrast to the weak-field AMM found by Schwinger, in the strong magnetic field region the AMM depends on the Landau level and decreases with it. The effects of the AMM in the EoS of a dense medium are investigated at strong and weak fields using the appropriate AMM expression for each case. In contrast with what has been reported in other works, we find that the AMM of charged fermions makes no significant contribution to the EoS at any field value.

hep-ph↗

arXiv2015

Maximum mass of magnetic white dwarfs

We revisit in this work the problem of the maximum masses of magnetized White Dwarfs (WD). The impact of a strong magnetic field onto the structure equations is addressed. The pressures become anisotropic due to the presence of the magnetic field and split into a parallel and perpendicular components. We first construct stable solutions of TOV equations for the parallel pressures, and found that physical solutions vanish for the perpendicular pressure when $B \gtrsim 10^{13}$ G. This fact establishes an upper bound for a magnetic field and the stability of the configurations in the (quasi) spherical approximation. Our findings also indicate that it is not possible to obtain stable magnetized WD with super Chandrasekhar masses because the values of the magnetic field needed for them are higher than this bound. To proceed into the anisotropic regime, we derived structure equations appropriated for a cylindrical metric with anisotropic pressures. From the solutions of the structure equations in cylindrical symmetry we have confirmed the same bound for $B \sim 10^{13} $ G, since beyond this value no physical solutions are possible. Our tentative conclusion is that massive WD, with masses well beyond the Chandrasekhar limit do not constitute stable solutions and should not exist.

astro-ph.HE↗

arXiv2014

Anisotropic stellar structure equations for magnetized stars

The fact that a magnetic field in a fermion system breaks the spherical symmetry suggest that the intrinsic geometry of this system is axisymmetric rather than spherical. In this work we analyze the impact of anisotropic pressures, due to the presence of a magnetic field, in the structure equations of a magnetized quark star. We assume a cylindrical metric and an anisotropic energy momentum tensor for the source. We found that there is a maximum magnetic field that the star can sustain, closely related to the violation of the virial relations.

astro-ph.HE↗

arXiv2014

Effects of AMM on the EoS of Magnetized Dense Systems

We investigate the effects of the anomalous magnetic moment (AMM) in the EoS of a fermion system in the presence of a magnetic field. In the region of strong magnetic fields ($B>m^2$) the AMM is found from the one-loop fermion self-energy. In contrast to the weak-field AMM found by Schwinger, in the strong magnetic field case, the AMM depends on the Landau level (LL) and decreases with it. The effects of the AMM in the EoS at intermediate-to-large fields can be found introducing the one-loop, LL-dependent AMM in the effective Lagrangian that is then used to find the thermodynamic potential of the system. We compare the plots of the parallel and perpendicular pressures versus the magnetic field in the strong field region considering the LL-dependent AMM, the Schwinger AMM, and no AMM at all. The results clearly show a separation between the physical magnitudes found using the Schwinger AMM and the LL-dependent AMM. This is an indication of the inconsistency of considering the Schwinger AMM beyond the weak field region $B< m^2$ where it was originally found. The curves for the EoS, pressures and magnetization at different fields give rise to the well-known de Haas van Alphen oscillations, associated to the change in the number of LL contributing at different fields.

nucl-th↗

arXiv2013

Anomalous-Magnetic-Moment Effects in a Strongly Magnetized and Dense Medium

We investigate the quantum corrections of the anomalous magnetic moment (AMM) for fermions in the presence of a strong magnetic field using the Ritus's approach. At strong fields the particles get different AMM's depending on the LL's. This result is different from what is obtained with the Schwinger's approximation at weak field where the AMM is independent of the LL. We analyze the significance of the AMM contribution to the Equation of State (EoS) of the magnetized system, in the weak and strong field approximations.

nucl-th↗

arXiv2011

Magnetized strangelets at finite temperature

The main properties of magnetized strangelets, namely, their energy per baryon, radius and electric charge, are studied. Temperature effects are also taken into account in order to study their stability compared to the 56Fe isotope and non-magnetized strangelets using the liquid drop model. Massive quarks are considered with the aim to have a more realistic description for strangelets in the astrophysical context and the environment of heavy ion colliders, playing also an important role in the thermodynamical quantities of the quark gas. It is concluded that the presence of a magnetic field tends to stabilize more the strangelets, even when temperature effects are taken into account. Magnetized strangelets in a paired superconductor phase (magnetized color flavor locked phase) are also discussed. It is shown that they are more stable than ordinary magnetized strangelets for typical gap values of the order of O(100) MeV.

hep-ph↗

arXiv2010

Magnetized color flavor locked state and compact stars

The stability of the color flavor locked phase in the presence of a strong magnetic field is investigated within the phenomenological MIT bag model, taking into account the variation of the strange quark mass, the baryon density, the magnetic field, as well as the bag and gap parameters. It is found that the minimum value of the energy per baryon in a color flavor locked state at vanishing pressure is lower than the corresponding one for unpaired magnetized strange quark matter and, as the magnetic field increases, the energy per baryon decreases. This implies that magnetized color flavor locked matter is more stable and could become the ground state inside neutron stars. The mass-radius relation for such stars is also studied.

astro-ph.HE↗

arXiv2010

Magnetic field effects on some astrophysical properties of Quark Stars

This thesis aims to study how amending certain astrophysical observable of quark stars due to presence of magnetic field. To do this we need to obtain Equation of State (EOS) and consider the stability of Strange Quark Matter (made up of quarks u, d and s) cold dense and magnetized in stellar equilibrium (beta equilibrium, conservation of the baryonic number and charge neutrality). We will work using the phenomenological MIT Bag model. The stability of the Magnetized Strange Quark Matter (MSQM) is studied taking into account the variation of parameters from the model: s quark mass, baryonic density, magnetic field and the Bag parameter. Results obtained were compared with those of magnetized normal quark matter (only u and d quarks in beta equilibrium) as well as the Strange Quark Matter (SQM). It is found that the energy per baryon decreases with the increasing magnetic field which implies that the MSQM is more stable than SQM. The Equations of State previously obtained are used to obtain stable configurations of magnetized strange stars checking that the magnetic field helps to reduce Mass-Radius (M-R) ratio of the star.

astro-ph.HE↗