Presence Of Strong Magnetic Field Research Articles

Masses and decay widths of charmonium states in the presence of strong magnetic fields

The masses and decay widths of charmonium states are studied in the presence of strong magnetic fields. The mixing between the pseudoscalar and vector charmonium states at rest is observed to lead to appreciable negative (positive) shifts in the masses of the pseudoscalar (longitudinal component of the vector) charmonium states in vacuum/hadronic medium in the presence of high magnetic fields. The pseudoscalar and vector charmonium masses in the hadronic medium, calculated in an effective chiral model from the medium changes of a scalar dilaton field, have additional significant modifications due to the mixing effects. The masses of the $D$ and $\bar D$ mesons in the magnetized hadronic matter are calculated within the chiral effective model. The partial decay widths of the vector charmonium state to $D\bar D$ are computed using a field theoretical model for composite hadrons with quark/antiquark constituents, and are compared to the decay widths calculated using an effective hadronic Lagrangian. The effects of the mixing are observed to lead to significant contributions to the masses of the pseusoscalar and vector charmonium states, and an appreciable increase in the decay width $\psi(3770) \rightarrow D\bar D$ at large values of the magnetic fields. These studies of the charmonium states in strong magnetic fields should have observable consequences on the dilepton spectra, as well as on the production of the open charm mesons and the charmonium states in ultra relativistic heavy ion collision experiments.

Searching optimum equations of state of neutron star matter in strong magnetic fields with rotation

Abstract Masses and radii of neutron stars are obtained in the presence of strong magnetic fields together with rotation. Mass-radius relations are calculated using 11 equations of state (EoSs: GM1, TM1-a, TM1-b, TM2$\omega\rho$-a, TM2$\omega\rho$-b, NL3-a, NL3-b, NL3$\omega\rho$-a, NL3$\omega\rho$-b, DDME2-a and DDME2-b) in relativistic mean field (RMF) theory. Obtained masses are over and around twice the solar mass ($M_\odot$) for all EoSs in the presence of strong magnetic fields of $3 \times 10^{18}$ G at the center. For NL3$\omega\rho$-a and NL3$\omega\rho$-b EoSs, masses are more than $M=2.17\,M_\odot$(observed maximum mass: $2.14\,M_\odot$) even without magnetic fields. Rotational effects are found to be insignificant in any case, at least up to the Kepler frequency. Suitable EoSs are also selected concerning the constraint on the radius of a neutron star.

Magnetic fields in compact stars and related phenomena

Magnetic fields appear at all scales in the Universe, spanning many orders of magnitude in their strength, and intervening in the development of many astrophysical processes. In particular, in compact objects, magnetic fields can reach huge intensities and play a fundamental role in the evolution of the star and its surroundings. In this review, the most relevant ideas about their generation mechanisms and their eects on the composition and evolution of compact stars are summarized. The review highlights the role played by anisotropic pressures, induced by the presence of strong magnetic fields, in the equation of state and in the macroscopic observables of compact objects. Anisotropies demand to solve Einstein equations beyond the sphericalsymmetry. In this regard, two models are analyzed, one using a metric in cylindrical coordinates and another one considering a metric, which allows to take into account small deformations of the objects. These results are relevant for the description of magnetized white dwarfs and hypothetical quark and Bose-Einstein condensate stars. Some related astrophysical phenomena, as pulsar kick velocities and jets associated to compact objects, are also addressed as a consequence of the presence of strong magnetic fields.

Creation and dissipation of magnetic fields in non-ideal GRMHD simulations

Compact objects, such as neutron stars and black holes, are characterized by the presence of strong magnetic fields that are crucial to explain the high-energy emission from these sources. Such magnetic fields may be subject to complex evolution inside the hosting relativistic plasmas, like dynamo-like processes amplifying initial seed fields in accretion disks or in the early stages of neutron star formation, or dissipative reconnection events in thin current sheets, as believed to occur in the magnetospheres of magnetars. Here we present a unified treatment of these non-ideal effects within the framework of general relativistic magnetohydrodynamics (GRMHD). Results of recent numerical simulations obtained with the ECHO code will be briefly discussed for selected test cases.

Similarity solutions for the strong shock waves in magnetogasdynamics with the effect of monochromatic radiation

In this paper, the method of invariance of Lie group is used to find the similarity solutions of the cylindrical shock waves for one-dimensional unsteady flow in magnetogasdynamics in the presence of monochromatic radiation. The density is assumed to be non-uniform ahead of the shock. The radiation flux is assumed to move through the gas. It is also shown that how the radiation parameter, ambient density exponent, ratio of specific heats (adiabatic constant) and the initial magnetic field strength affect the profiles of the flow variables. It is found that the shock wave decays in the presence of strong magnetic field and shows reverse behavior in the case of monochromatic radiation, i.e., the shock wave grows faster in the presence of radiation. To obtain the similarity solutions and the profiles of the flow variables, numerical calculations are performed using the software package MATHEMATICA.

Effect of magnetic field on the charge and thermal transport properties of hot and dense QCD matter

We have studied the effect of strong magnetic field on the charge and thermal transport properties of hot QCD matter at finite chemical potential. For this purpose, we have calculated the electrical conductivity (sigma _mathrm{el}) and the thermal conductivity (kappa ) using kinetic theory in the relaxation time approximation, where the interactions are subsumed through the distribution functions within the quasiparticle model at finite temperature, strong magnetic field and finite chemical potential. This study helps to understand the impacts of strong magnetic field and chemical potential on the local equilibrium by the Knudsen number (Omega ) through kappa and on the relative behavior between thermal conductivity and electrical conductivity through the Lorenz number (L) in the Wiedemann–Franz law. We have observed that, both sigma _mathrm{el} and kappa get increased in the presence of strong magnetic field, and the additional presence of chemical potential further increases their magnitudes, where sigma _mathrm{el} shows decreasing trend with the temperature, opposite to its increasing behavior in the isotropic medium, whereas kappa increases slowly with the temperature, contrary to its fast increase in the isotropic medium. The variation in kappa explains the decrease of the Knudsen number with the increase of the temperature. However, in the presence of strong magnetic field and finite chemical potential, Omega gets enhanced and approaches unity, thus, the system may move slightly away from the equilibrium state. The Lorenz number (kappa /(sigma _mathrm{el} T)) in the abovementioned regime of strong magnetic field and finite chemical potential shows linear enhancement with the temperature and has smaller magnitude than the isotropic one, thus, it describes the violation of the Wiedemann–Franz law for the hot and dense QCD matter in the presence of a strong magnetic field.

Three-dimensional heat transfer effects in external layers of a magnetized neutron star

ABSTRACT Determination of a magnetic field structure on a neutron star (NS) surface is an important problem of a modern astrophysics. In a presence of strong magnetic fields, a thermal conductivity of a degenerate matter is anisotropic. In this paper, we present 3D anisotropic heat transfer simulations in outer layers of magnetized NSs, and construct synthetic thermal light curves. We have used a different from previous works tensorial thermal conductivity coefficient of electrons, derived from the analytical solution of the Boltzmann equation by the Chapman–Enskog method. We have obtained an NS surface temperature distribution in presence of dipole-plus-quadrupole magnetic fields. We consider a case, in which magnetic axes of a dipole and quadrupole components of the magnetic field are not aligned. To examine observational manifestations of such fields, we have generated thermal light curves for the obtained temperature distributions using a composite blackbody model. It is shown that the simplest (only zero-order spherical function in quadrupole component) non-coaxial dipole-plus-quadrupole magnetic field distribution can significantly affect the thermal light curves, making pulse profiles non-symmetric and amplifying pulsations in comparison to the pure-dipolar field.

The importance of magnetic fields for the initial mass function of the first stars

ABSTRACT Magnetic fields play an important role for the formation of stars in both local and high-redshift galaxies. Recent studies of dynamo amplification in the first dark matter haloes suggest that significant magnetic fields were likely present during the formation of the first stars in the Universe at redshifts of 15 and above. In this work, we study how these magnetic fields potentially impact the initial mass function (IMF) of the first stars. We perform 200 high-resolution, three-dimensional (3D), magnetohydrodynamic (MHD) simulations of the collapse of primordial clouds with different initial turbulent magnetic field strengths as predicted from turbulent dynamo theory in the early Universe, forming more than 1100 first stars in total. We detect a strong statistical signature of suppressed fragmentation in the presence of strong magnetic fields, leading to a dramatic reduction in the number of first stars with masses low enough that they might be expected to survive to the present-day. Additionally, strong fields shift the transition point where stars go from being mostly single to mostly multiple to higher masses. However, irrespective of the field strength, individual simulations are highly chaotic, show different levels of fragmentation and clustering, and the outcome depends on the exact realization of the turbulence in the primordial clouds. While these are still idealized simulations that do not start from cosmological initial conditions, our work shows that magnetic fields play a key role for the primordial IMF, potentially even more so than for the present-day IMF.

Suppression of luminosity and mass–radius relation of highly magnetized white dwarfs

ABSTRACT We explore the luminosity L of magnetized white dwarfs and its effect on the mass–radius relation. We self-consistently obtain the interface between the electron degenerate-gas dominated inner core and the outer ideal gas surface layer or envelope by incorporating both the components of gas throughout the model white dwarf. This is obtained by solving the set of magnetostatic equilibrium, photon diffusion, and mass conservation equations in the Newtonian framework, for different sets of luminosity and magnetic field. We appropriately use magnetic opacity, instead of Kramer’s opacity, wherever required. We show that the Chandrasekhar limit is retained, even at high luminosity up to about $10^{-2}\, L_\odot$ but without magnetic field, if the temperature is set constant inside the interface. However, there is an increased mass for large-radius white dwarfs, an effect of photon diffusion. Nevertheless, in the presence of strong magnetic fields, with central strength of about 1014 G, super-Chandrasekhar white dwarfs, with masses of about $1.9\, {\rm M}_{\odot }$, are obtained even when the temperature inside the interface is kept constant. Most interestingly, small-radius magnetic white dwarfs remain super-Chandrasekhar even if their luminosity decreases to as low as about $10^{-20}\, L_{\odot }$. However, their large-radius counterparts in the same mass–radius relation merge with Chandrasekhar’s result at low L. Hence, we argue for the possibility of highly magnetized, low luminous super-Chandrasekhar mass white dwarfs that, owing to their faintness, can be practically hidden.

Polarized Radiation Signals from Highly Magnetized Neutron Star Surfaces

AbstractThe surfaces of neutron stars are likely sources of strongly polarized soft X rays due to the presence of strong magnetic fields. Scattering transport in the surface layers is critical to the determination of the emergent anisotropy of light intensity, and is strongly influenced by the complicated interplay between linear and circular polarization information. We have developed a magnetic Thomson scattering simulation to model the outer layers of fully-ionized atmospheres in such compact objects. Here we summarize emergent intensities and polarizations from extended atmospheric simulations, spanning considerable ranges of magnetic colatitudes. General relativistic propagation of light from the surface to infinity is fully included. The net polarization degrees are moderate and not very small when summing over a variety of field directions. These results provide an important foundation for observations of magnetars to be acquired by NASA’s new IXPE X-ray polarimeter and future X-ray polarimetry missions.

Modeling of spherical dust charging in collisionless magnetized plasmas with DiMPl

Determining the equilibrium charge of conducting spheres in plasmas is important for interpreting Langmuir probe measurements, plasma surface interactions, and dust particle behavior. The Monte Carlo code Dust in Magnetised Plasmas (DiMPl) has been developed for the purpose of determining the forces and charging behavior of conducting spheroids under a variety of conditions and benchmarked against previous numerical results. The floating potentials of spheres in isothermal, collisionless, hydrogen plasmas as a function of magnetic field strength and size relative to the Debye length are studied using DiMPl and compared with new results from the N-body tree code (pot) and recent particle in cell measurements. The results of all three simulations are similar, identifying a small range at modest ion magnetization parameters over which the electron current is reduced relative to the ion current. The potential as a function of magnetic field strength is found to be relatively insensitive to dust size for dust smaller than the Debye length. The potential of large dust is found to depend less strongly on flow speed for modest magnetic field strengths and to decrease with increasing flow speed in the presence of strong magnetic fields for smaller dust. A semi-empirical model for the potential of small dust in a collisionless plasma as a function of magnetic field strength is developed, which reproduces the expected currents and potentials in the high and low magnetic field limit.

Collective oscillations of Majorana neutrinos in strong magnetic fields and self-induced flavor equilibrium

We study collective oscillations of Majorana neutrinos in some of the most extreme astrophysical sites such as neutron star merger remnants and magneto-rotational core-collapse supernovae which include dense neutrino media in the presence of strong magnetic fields. We show that neutrinos can reach flavor equilibrium if neutrino transition magnetic moment ${\ensuremath{\mu}}_{\ensuremath{\nu}}$ is strong enough, namely when ${\ensuremath{\mu}}_{\ensuremath{\nu}}/{\ensuremath{\mu}}_{\mathrm{B}}\ensuremath{\gtrsim}{10}^{\ensuremath{-}14}--{10}^{\ensuremath{-}15}$ with ${\ensuremath{\mu}}_{\mathrm{B}}$ being the Bohr magneton. This sort of flavor equilibrium, which is not necessarily flavor equipartition, can occur on (short) scales determined by the strength of the magnetic term in the Hamiltonian. Our findings can have interesting implications for the physics of such violent astrophysical environments.

Inverse bremsstrahlung absorption in magnetized plasmas

The Magneto-Inertial Fusion (MIF) approach has the benefits of both approaches of Inertial Confinement Fusion (ICF) and Magnetic Confinement Fusion (MCF). MIF is a complete approach, as compared to others. It has the advancement of the common ICF and some advantages over MCF. It also includes high-density plasma in the presence of strong magnetic fields. In this study, we investigate the inverse bremsstrahlung absorption (IBA) in magnetized plasma and the kinetic theory. Many researchers have calculated the inverse bremsstrahlung absorption coefficient through the ICF approach. In this investigation, however, the average of IBA is obtained that can be used in the MIF approach, the kinetic theory and the Krook collision frequency. In addition, the influences of some parameters such as laser wavelength, electron temperature, and static magnetic field are shown on the mean collisional absorption. A numerical solution is also used to calculate the dispersion function and the laser electric field. IBA is one of the basic heating processes in laser fusion plasma. The results of the study show that, in critical layers, the increase of absorption is proportional to short laser wavelength, low electron temperature, but IBA varies slowly with the static magnetic field.

Computation of Non-isothermal Thermo-convective Micropolar Fluid Dynamics in a Hall MHD Generator System with Non-linear Distending Wall

A theoretical model for steady non-isothermal convective heat transfer in non-Newtonian magnetized micropolar gas flow from a non-linear stretching/contracting wall in the presence of strong magnetic field is presented, as a simulation of an MHD (magnetohydrodynamic) Hall energy generator. Subsonic flow is considered, and compressibility effects neglected. The strength of the magnetic field which is applied in the general case obliquely to the wall is sufficient to invoke the collective effects of Hall current and Ohmic heating (Joule dissipation). Viscous heating is also included in the energy balance. Deploying similarity transformations, the governing equations are normalized into nonlinear ordinary differential equations with associated boundary conditions. The non-linear boundary value problem thus posed is then solved computationally with Nachtsheim–Swigert iteration technique along with the fourth-fifth order Runge–Kutta integration method. Verification of solutions is obtained with the semi-analytical Homotopy analysis method. Further validation is conducted with the semi-numerical Adomian decomposition method. In both cases excellent agreement is obtained with the Runge–Kutta shooting quadrature solutions. Additional validation is conducted with earlier Newtonian studies in the absence of micropolar, Hall current and dissipation effects. The influence of local Grashof number, local Hartmann number, Eringen microrotational parameter, Eringen coupling vortex parameter, Prandtl number and Eckert number on non-dimensional velocity components (primary, secondary and angular) and temperature within the boundary layer are graphically illustrated and interpreted at length. Furthermore, the effects of the thermophysical (e.g. non-isothermal power law index), electromagnetic parameters (e.g. Hall parameter) and geometric parameter (wall extension/contraction parameter) on the skin-friction coefficient (i.e. primary and secondary shear stress and wall couple stress) and surface heat transfer rate (Nusselt number) are evaluated. The study is relevant to near wall transport phenomena in novel MHD Hall power generators.

3D Simulation of Anisotropic Heat Transfer in Outer Layers of Magnetized Neutron Stars

The results of three-dimensional numerical simulation of heat transfer in the outer layers of magnetized neutron stars are presented. Determining the structure of the magnetic field on a neutron star surface is an important task of modern astrophysics. In the presence of strong magnetic fields, the medium becomes anisotropic, and the laws of heat conduction change. The tensor coefficient of thermal conductivity for magnetized degenerate plasma was obtained by Bisnovatyi-Kogan and Glushikhina by solving the Boltzmann equation with the Chapman–Enskog method. In this paper, the temperature distribution on the surface of a magnetized neutron star is obtained for magnetic fields of the dipolar and quadrupolar type, as well as for their superposition. To numerically solve the stationary temperature distribution problem in the outer layers of a magnetized neutron star, the basic (support) operator numerical method was extended to a three-dimensional case. The problem was solved on the grid which consists of tetrahedra.

Experimental measurement of ionization chamber angular response and associated magnetic field correction factors in MR-linac.

To measure ionization chamber dose response as a function of the angle between magnetic field direction and ionization chamber orientation in magnetic resonance-guided radiation therapy (MRgRT) system, and to evaluate angular dependence of magnetic field correction factor for reference dosimetry. Measurements were performed on an Elekta MR-linac that integrates a 1.5-T Philips MRI and a 7-MV FFF photon beam accelerator. The response of four reference class chambers (Exradin-A19, A1SL, IBA FC65-G, and CC13, paired with a PTW UE electrometer) was studied. An in-house built MR-compatible water tank and an accompanying cylindrical insert that allowed chamber rotation around the cylinder's axis was used. The EPID onboard imaging was used to center chamber at the MR-linac isocenter (143.5cm, SAD), as well as to verify position at each datapoint. A clear angular dependence of dose response for all chambers has been measured. The most significant effect of magnetic field on relative chamber response in the presence of magnetic field was observed in the orientation when chamber axis is perpendicular to the direction of magnetic field with the tip pointing in the same direction as Lorentz force. This effect is more pronounced for larger volume chambers; the maximum relative variation in the chamber response (between the setup described above and the one where chamber and magnetic field are parallel) is a 5.3% and 4.6% increase for A19 and FC65-G, respectively, and only 2.0% and 1.9% for smaller volume A1SL and CC13 chamber, respectively. We measured the absolute magnitude of the magnetic field correction factor for the Exradin-A19, A1SL, IBA FC65-G, and CC13 to be 0.938±1.13%, 0.968±0.99%, 0.950±1.13%, and 0.975±1.13%, respectively. The values are for perpendicular orientation of the chamber relative to magnetic field and parallel to the Lorentz force. Experimental measurements carried out in this study have verified the optimal orientation of ionization chamber in terms of minimizing effect of magnetic field on the chamber dose response. This study provides a detailed high-resolution measurement of absolute values for four reference class chambers as a function of the angle between ionization chamber's central axis and the direction of strong magnetic field over a full 360° rotation. The experimental results of this study can further be used for optimization of the actual sensitive volume of the chamber (and analysis of dead volume) in future Monte Carlo chamber simulations in the presence of strong magnetic fields. In addition, it will provide some necessary data for future reference dosimetry protocols for MR-linac.

RMATE: A device to test radiation-induced effects under controlled magnetic field and temperature

This study shows the development and performance assessment of a novel set-up that enables the research of structural materials for fusion reactors, by making possible simultaneous application of temperature (up to 450 °C) and magnetic field (close to 0.6 T) during irradiation experiments. These aspects become critical as structural materials in fusion reactors are exposed to intense radiation levels under the presence of strong magnetic fields. Moreover, material microstructure could be modified by radiation-induced propagating defects, which are thought to be sensitive to magnetic fields. The device has three main components: magnetic closure, sample holder with integrated heater, and radiation shield. It is provided with a thermal shield to prevent other elements of the device to heat up and fail. A mapping of the magnetic flux in the region where sample and heater are located has been modeled by finite elements simulation software and correlated with magnetic measurements.

Landau damping in a strong magnetic field: Dissociation of quarkonia

In this article we have investigated the effects of strong magnetic field on the properties of quarkonia immersed in a thermal medium of quarks and gluons and then studied the quasi-free dissociation of quarkonia due to the Landau-damping. Thermalising the Schwinger propagator for quarks in the lowest Landau levels and the Feynman propagator for gluons in real-time formalism, we have calculated the resummed retarded and symmetric propagators, which in turn give the real and imaginary components of dielectric permittivity, respectively. Finally the inverse Fourier transform of the permittivities encrypt the effect of hot QCD medium in the presence of strong magnetic field into both real and imaginary parts of heavy quark potential. We have found that the magnetic field largely affects the large-distance interaction, as a result, the real part of potential becomes more attractive and the magnitude of imaginary part too becomes larger, compared to its counterpart in the absence of magnetic field. The real part of the potential is thereafter solved numerically by the Schrödinger equation to obtain the energy eigenvalues and energy eigenfunctions of the charmonium states. We have noticed that in the presence of strong magnetic field, the size (r2) of J/ψ and ψ′ are swelled whereas χc gets shrunk, unless the temperature is very high. Similarly the magnetic field affects the binding of J/ψ and χc differently, i.e. it decreases the binding of J/ψ but increases for χc. On contrary the magnetic field increases the width of the resonances, unless the temperature is sufficiently high. We have finally studied the dissociation due to the Landau damping and found that the dissociation temperatures become higher in the presence of magnetic field. For example, with eB=6mπ2 the J/ψ is dissociated at 2Tc, and with eB=4mπ2 the χc is dissociated at 1.1Tc in comparison, with eB = 0 the J/ψ is dissociated at T=1.6Tc and χc is dissociated at T=0.8Tc. However, with the further increase of magnetic field the dissociation temperatures decrease.

Induced charge and electric field in dense magnetized fermionic medium at finite temperature

The one-photon vertex in presence of strong magnetic field and finite temperature in dense medium is computed, its properties are investigated. Calculations are performed in analytical forms for two cases: at zero temperature and at high temperature. The integral form of the vertex is obtained for a general case. The tensor function is represented as the sum of Feynmanʼs one-loop diagrams. The induced charge dependence on chemical potential, temperature, and strong magnetic field is investigated in detail. The induced potential is calculated for the case of the infinite medium plate.

Thermomagnetic properties and Bjorken expansion of hot QCD matter in a strong magnetic field

In this work we have studied the effects of an external strong magnetic field on the thermodynamic and magnetic properties of a hot QCD matter and then explored these effects on the subsequent hydrodynamic expansion of the said matter once produced in the ultrarelativistic heavy ion collisions. For that purpose, we have computed the quark and gluon self-energies up to one loop in the strong magnetic field, using the HTL approximation with two hard scales - temperature and magnetic field, which in turn compute the effective propagators for quarks and gluons, respectively. Hence the quark and gluon contributions to the free energy are obtained from the respective propagators and finally derive the equation of state (EOS) by calculating the pressure and energy density. We have found that the speed of sound is enhanced due to the presence of strong magnetic field and this effect will be later exploited in the hydrodynamics. Thereafter the magnetic properties are studied from the free energy of the matter, where the magnetization is found to increase linearly with the magnetic field, thus hints the paramagnetic behavior. The temperature dependence of the magnetization is also studied, where the magnetization is found to increase slowly with the temperature. Finally, to see how a strong magnetic field could affect the hydrodynamic evolution, we have revisited the Bjorken boost-invariant picture with our paramagnetic EOS as an input in the equation of motion for the energy-momentum conservation. We have noticed that the energy density evolves faster than in the absence of strong magnetic field, i.e. cooling becomes faster, which could have implications on the heavy-ion phenomenology. As mentioned earlier, this observation can be understood by the enhancement of the speed of sound.