Effect Of Anomalous Magnetic Moment Research Articles

Effect of anomalous magnetic moment on the chiral transition at zero temperature in a strong magnetic field

The effect of the anomalous magnetic moment (AMM) on the chiral restoration is investigated at zero temperature in the strong magnetic fields with the vacuum magnetic regularization scheme. It is shown that the chiral restoration diagram sensitively depends on the AMM in the ultrastrong magnetic fields. In our work, the parameterization of AMM is employed as proportional to the square of the chiral condensate. The critical chemical potential is found to decrease linearly by the increasing coefficient in the AMM scale. At a smaller scale of the AMM, the critical chemical potential could go down and then grow up as the magnetic field increases. But at a larger scale, the magnetic catalysis on the critical chemical potential would not happen anymore.

Cold Quark–Gluon Plasma EOS Applied to a Magnetically Deformed Quark Star with an Anomalous Magnetic Moment

We consider a QCD cold-plasma-motivated Equation of State (EOS) to examine the impact of an Anomalous Magnetic Moment (AMM) coupling and small shape deformations on the static oblate and prolate core shapes of quark stars. Using the Fogaça QCD-motivated EOS, which shifts from the high-temperature, low-chemical-potential quark–gluon plasma environment to the low-temperature, high-chemical-potential quark stellar core environment, we consider the impact of an AMM coupling with a metric-induced shape deformation parameter in the Tolman–Oppenheimer–Volkov (TOV) equations. The AMM coupling includes a phenomenological scaling that accounts for the weak and strong field characteristics in dense matter. The EOS is developed using a hard gluon and soft gluon decomposition of the gluon field tensor and using a mean-field effective mass for the gluons. The AMM is considered using the Dirac spin tensor coupled to the EM field tensor with quark-flavor-based magnetic moments. The shape parameter is introduced in a metric ansatz that represents oblate and prolate static stellar cores for modified TOV equations. These equations are numerically solved for the final mass and radius states, representing the core collapse of a massive star with a phase transition leading to an unbound quark–gluon plasma. We find that the combined shape parameter and AMM effects can alter the coupled EOS–TOV equations, resulting in an increase in the final mass and a decrease in the final equatorial radius without collapsing the core into a black hole and without violating causality constraints; we find maximum mass values in the range 1.6 Mʘ < M < 2.5 Mʘ. These states are consistent with some astrophysical, high-mass magnetar/pulsar and gravity wave systems and may provide evidence for a core that has undergone a quark–gluon phase transition such as PSR 0943 + 10 and the secondary from the GW 190814 event.

Insignificance of the anomalous magnetic moment of the quarks in presence of chiral imbalance

We incorporate the anomalous magnetic moment (AMM) of quarks in the framework of PNJL model to study hot and dense magnetised matter with chiral imbalance. For this purpose, the eigen energy solution of the Dirac equation is obtained in presence of constant background magnetic field and chiral chemical potential (CCP) along with the minimal anomalous magnetic moment interaction of the fermion. Although there is a marginal enhancement in the IMC behaviour of the quark condensate due to the combined effects of AMM and CCP, we find that the overall behaviour of the Polyakov loop and the chiral charge density is dominated by the chiral chemical potential. It is further shown that the AMM effects in presence of CCP remains insignificant even after consideration of thermo-magnetically modified moments.

Open bottom mesons in asymmetric nuclear matter in the presence of strong magnetic fields

The modifications of the masses of the $B$ and $\bar B$ mesons in asymmetric nuclear matter in the presence of strong magnetic fields, are investigated using a chiral effective model. The medium modifications of these open bottom mesons arise due to their interactions with the scalar mesons and the nucleons. In the magnetized nuclear matter, the proton has contributions from the Landau levels. In the chiral effective model, the masses of the $B$ and $\bar B$ are calculated from the leading term, namely the vectorial Weinberg Tomozawa term as well as from the next to leading order contributions, i.e., due to the scalar exchange and the range terms. Due to the Weinberg-Tomozawa term, the $\bar B$ mesons experience an attractive interaction in the symmetric nuclear matter, whereas the $B$ mesons have a repulsive interaction. Inclusion of the contributions from the scalar exchange and the range terms as well, leads to drop of the masses of both $B$ and $\bar B$ mesons. The effect of the isospin asymmetry breaks the mass degeneracy of the $B^+$ and $B^0$ (as well as of the $B^-$ and $\bar {B^0}$) mesons, and its effect is observed to be large at high densities. The effects of anomalous magnetic moments of the nucleons are taken into account in the present study of the masses of the open bottom mesons in magnetized nuclear matter.

Dynamical screening of AMM and QED effects for large-Z hydrogen-like atoms

The effective interaction ΔU AMM of the anomalous magnetic moment (AMM) of an electron with the Coulomb field of an extended nucleus is analyzed. As soon as the q 2 dependence of the electron formfactor F 2(q 2)is taken into account from the beginning, the AMM is found to be dynamically screened at small distances of r ≪ 1/m. The ΔU AMM effects on the low-lying electronic levels of a superheavy extended nucleus with Zα > 1are analyzed using the nonperturbative approach. The growth rate of the ΔU AMM contribution with increasing Z is shown to be essentially nonmonotonic. At the same time, the energy shifts of electronic levels in the vicinity of the threshold of the lower continuum monotonically decrease in the region Z ≫Z cr,1s . The latter result is generalized to the whole self-energy contribution to energy shifts of electronic levels, thus also referring to the possible behavior of QED radiative effects with virtual-photon exchange, considered beyond the framework of the perturbative expansion in Zα.

Neutron stars including the effects of chaotic magnetic fields and anomalous magnetic moments**Supported by National Natural Science Foundation of China (11535004, 11375086, 11120101005, 11175085, 11235001), 973 National Major State Basic Research and Development of China (2013CB834400), and Science and Technology Development Fund of Macau (068/2011/A)

The relativistic mean field (RMF) FSUGold model extended to include hyperons is employed to study the properties of neutron stars with strong magnetic fields. The chaotic magnetic field approximation is utilized. The effect of anomalous magnetic moments (AMMs) is also investigated. It is shown that the equation of state (EOS) of neutron star matter is stiffened by the presence of the magnetic field, which increases the maximum mass of a neutron star by around 6%. The AMMs only have a small influence on the EOS of neutron star matter, and increase the maximum mass of a neutron star by 0.02Msun. Neutral particles are spin polarized due to the presence of the AMMs.

Relativistic elastic scattering of hydrogen atoms by positron impact with anomalous magnetic moment effects

Elastic scattering of hydrogen atoms by positron impact is studied at various values of incident positron energy and laser intensities. A discussion of differential cross-sections for positron scattering by hydrogen atoms in presence of laser field is presented along with anomalous magnetic moment of both electrons and positrons fully included. Differential cross sections for electrons and positrons remain almost equal in absence of anomalous magnetic moment effects. A comparison is also made with introduction of anomalous magnetic moment effects of both electrons and positrons. At intensities equal to 0.05 a.u. and above significant discrepancies in differential cross section is found even in first Born approximation.

Effect of anomalous magnetic moment on thermodynamic properties of weakly interacting Fermi gas in weak magnetic field

Taking the anomalous magnetic moment into consideration, the analytical expression of the free energy for a weakly interacting Fermi gas in a weak magnetic field is derived by using the pseudopotential method and thermodynamic theory, therefore the thermodynamic properties can be studied. Based on the derived expression, the thermodynamic properties of this system at both high and low temperatures are given, and the effect of anomalous magnetic moment on thermodynamic properties can be analyzed. The effect of anomalous magnetic moment on the thermodynamic properties is related to temperature, and with the rise of temperature this effect increases in the low temperature zone, but decreases in the high temperature zone. For the chemical potential and internal energy of the system, the anomalous magnetic moment strengthens the influence of the magnetic field, but weakens the influence of the interaction. Under the influence of anomalous magnetic moment, the heat capacity of the system decreases in the low temperature zone, but increases in the high temperature zone.

Anomalous magnetic moment of hot quarks, inverse magnetic catalysis, and reentrance of the chiral symmetry broken phase

The effect of anomalous magnetic moment of quarks on thermodynamic properties of the chiral condensate is studied, using of a two-flavor Nambu--Jona-Lasinio model at finite temperature $T$, chemical potential $\mu$, and in the presence of a uniform magnetic field $eB$. To this purpose, the Schwinger linear-in-$B$ ansatz for the quark anomalous magnetic moment in term of the nonperturbative Bohr magneton is considered. In a two-dimensional flavor space, it leads to the correction $\hat{T}_{Sch}=\hat{\kappa}\hat{Q} eB$ in the energy dispersion relation of quarks. Here, $\hat{Q}$ is the quark charge matrix. We consider three different sets for $\hat{\kappa}$, and numerically determine the dependence of the constituent quark mass on $T,\mu$ and $eB$ for fixed $\hat{\kappa}$. By exploring the complete phase portrait of this model in $T$-$\mu$, $\mu$-$eB$, and $T$-$eB$ phase spaces for various fixed $eB$, $T$, $\mu$ and $\hat{\kappa}$, we observe that inverse magnetic catalysis occurs for large enough $\hat{\kappa}$. Moreover, in the regime of weak magnetic fields, the phenomenon of reentrance of chiral symmetry broken and restored phases occurs for $T, \mu$ and $eB$ dependent $\hat{\kappa}$.

Effects of AMM on the EoS of magnetized dense systems

AbstractWe 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 > m2) the AMM is found from the one‐loop fermion selfenergy. 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 thermodynamical 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 < m2 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. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron impact excitation of hydrogen atom with anomalous magnetic moment effects

In framework of first Born approximation, Salamin wave states have been used to calculate the differential cross section for laser assisted semirelativistic 1s–2s excitation of hydrogen atom by electron impact with anomalous magnetic moment effects fully included. The obtained results have been compared with laser assisted relativistic differential cross section without such effects. It is found that the electron’s anomalous magnetic moment effects in laser assisted 1s–2s excitation is very important particularly with increase of intensity. Good agreement with laser assisted differential cross section without anomalous magnetic moment effects is obtained when electron’s anomaly \(\kappa=4a_{e^-}=2(g-2)\) is taken to be zero.

Muon's Anomalous Magnetic Moment Effects on Laser Assisted Coulomb Scattering Process

Laser assisted Coulomb scattering by relativistic electron and heavy electron (muon) is studied by using Salamin waves [3] in the Weak Field Approximation (WFA). Both electron and muon are described by the Dirac equation, with the anomalous magnetic moment effects fully included. The generalization of this paper to heavy electron (muon) gives interesting insights as to how the mass affects the magnitude of the differential cross sections. No significant difference in the muon’s DCS with and without AMM effects was detected. PACS: 34.80.Dp, 12.20.Ds

Electron’s anomalous magnetic-moment effects on electron-hydrogen elastic collisions in the presence of a circularly polarized laser field

The effect of the electron's anomalous magnetic moment on the relativistic electronic dressing for the process of electron-hydrogen atom elastic collisions is investigated. We consider a laser field with circular polarization and various electric field strengths. The Dirac-Volkov states taking into account this anomaly are used to describe the process in the first order of perturbation theory. The correlation between the terms coming from this anomaly and the electric field strength gives rise to new results, namely the strong dependence of the spinor part of the differential cross section (DCS) with respect to these terms. A detailed study has been devoted to the non relativistic regime as well as the moderate relativistic regime. Some aspects of this dependence as well as the dynamical behavior of the DCS in the relativistic regime have been addressed.

Nucleon-nucleon bremsstrahlung: Anomalous magnetic moment effects

Background: Two soft-photon amplitudes, the two-u-two-t special ( TuTts) amplitude and the Low amplitude, are known to produce quantitatively similar npy cross sections, but they predict quite different pp. cross sections for those kinematic conditions in which the nucleon scattering angles are small ( less than 25 degrees.). Purpose: These two amplitudes have been applied to systematically investigate three different nucleon-nucleon bremsstrahlung ( NN gamma) processes: pp gamma, np gamma, and nn gamma. The nn gamma process is explored for the first time. The primary focus of this work is to investigate the contribution of the proton and the neutron anomalous magnetic moments to all three NN gamma processes for projectile energies above 150 MeV and for laboratory scattering angles (theta(1) and theta(2)) lying between 8 degrees and 40 degrees. Method: A special soft-photon expansion in which the TuTts amplitude is expanded in terms of the Low amplitude plus additional amplitudes is utilized to explore the relationship between the TuTts and Low amplitudes and the reasons why they agree and disagree. We also used the TuTts amplitude to calculate the NN gamma cross section with and without the anomalous magnetic moment contributions to explore the importance of that element of the electromagnetic current. Results: The TuTts amplitude describes well the available pp. cross- section data. The anomalous magnetic moment contribution is ( i) significant in the pp. process when each scattering angle is less than 25 degrees but insignificant when each scattering angle is 40 degrees or greater and ( ii) insignificant in the np gamma process for all scattering angles. The nn. cross sections for the TuTts and Low amplitudes differ substantially for the kinematics investigated. Conclusions: In general, the Low amplitude agrees well with the TuTts amplitude when anomalous magnetic moment effects are not significant, but the two amplitudes can yield quite different predictions when such effects are significant. These findings have enhanced our understanding of the fundamental emission mechanism governing NN gamma processes, and they explain why the TuTts amplitude should be used to describe all three NN gamma processes.

Variational two-fermion wave equations in quantum electrodynamics: Muoniumlike systems

We consider a reformulation of quantum electrodynamics in which covariant Green functions are used to solve for the electromagnetic field in terms of the fermion fields. The resulting modified Hamiltonian contains the photon propagator directly. A simple Fock-state variational trial function is used to derive relativistic two-fermion equations variationally from the expectation value of the Hamiltonian of the field theory. The interaction kernel of the equation is shown to be, in essence, the invariant M matrix in lowest order. Solutions of the two-body equations are presented for muoniumlike systems for small coupling strengths. The results compare well with the observed muonium spectrum, as well as that for hydrogen and muonic hydrogen. Anomalous magnetic moment effects are discussed.

Effects of Anomalous Magnetic Moment in the Quantum Motion of Neutral Particle in Magnetic and Electric Fields Produced by a Linear Source in a Conical Spacetime

In this paper we analyse the effect of the anomalous magnetic moment on the non-relativistic quantum motion of a neutral particle in magnetic and electric fields produced by linear sources of constant current and charge density, respectively.

Anomalous Magnetic Moments

The Dirac equation explained why the gyromagnetic ratio, g factor, is equal to 2 for fundamental spin [Formula: see text] particles. Quantum loop effects were subsequently shown to induce a small shift or anomaly, a≡(g-2)/2. Anomalous magnetic moment effects have been calculated and measured with extraordinary precision for the electron and muon. Here, the Standard Model's predictions for al=(gl-2)/2, l=e, μ are described and compared with experimental values. Implications for probing "New Physics" effects are also discussed.

NUCLEAR MATTER IN INTENSE MAGNETIC FIELD AND WEAK PROCESSES

We study the effect of magnetic field on the dominant neutrino emission processes in neutron stars. The processes are first calculated for the case when the magnetic field does not exceed the critical value to confine electrons to the lowest Landau state. We consider here magnetic fields up to ~1019 Gauss. We find that fields of strength 1015-1016 Gauss have significant effect on the neutronization process, for the direct URCA process the effect of the magnetic field becomes significant only at ~1019 Gauss. In order to estimate the effect we derive the composition of cold nuclear matter at high densities and in beta equilibrium, a situation appropriate for neutron stars. The hadronic interactions are incorporated through the exchange of scalar and vector mesons in the framework of relativistic mean field theory. In addition the effects of anomalous magnetic moments of nucleons are also considered.

Anomalous magnetic moment effects in the radiative decay

We have calculated the differential probability of the radiative decay, , of the -lepton carrying an anomalous magnetic moment. Taking into account both the inner bremsstrahlung and the structure-dependent radiation contributions, we computed the double differential probability. Observables, which are particularly suitable for the full reconstruction of the vector and axial form factors, are identified and implications for the measurement of the anomalous magnetic moment of the -lepton are discussed.

Low energy limit of the Chern-Simons theory coupled to fermions

We study the nonrelativistic limit of the theory of a quantum Chern-Simons field minimally coupled to Dirac fermions. To get the nonrelativistic effective Lagrangian one has to incorporate vacuum polarization and anomalous magnetic moment effects. In addition to that, an unsuspected quartic fermionic interaction may also be induced. As a by-product, the method we use to calculate loop diagrams, separating low and high loop momenta contributions, allows us to identify how a quantum nonrelativistic theory nests in a relativistic one.