arXiv subjects

G. Mao

Publications and source records attributed to G. Mao.

7 recordsLinked to original sources

arXiv2006

Neutron spin polarization in strong magnetic fields

The effects of strong magnetic fields on the inner crust of neutron stars are investigated after taking into account the anomalous magnetic moments of nucleons. Energy spectra and wave functions for protons and neutrons in a uniform magnetic field are provided. The particle spin polarizations and the yields of protons and neutrons are calculated in a free Fermi gas model. Obvious spin polarization occurs when $B\geq10^{14}$G for protons and $B\geq10^{17}$G for neutrons, respectively. It is shown that the neutron spin polarization depends solely on the magnetic field strength.

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arXiv2004

Energy Spectra of Anti-nucleons in Finite Nuclei

The quantum vacuum in a many-body system of finite nuclei has been investigated within the relativistic Hartree approach which describes the bound states of nucleons and anti-nucleons consistently. The contributions of the Dirac sea to the source terms of the meson-field equations are taken into account up to the one-nucleon loop and one-meson loop. The tensor couplings for the $ω$- and $ρ$-meson are included in the model. The overall nucleon spectra of shell-model states are in agreement with the data. The calculated anti-nucleon spectra in the vacuum differ about 20 -- 30 MeV with and without the tensor-coupling effects.

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arXiv2003

Neutron star composition in strong magnetic fields

We study the problem of neutron star composition in the presence of a strong magnetic field. The effects of the anomalous magnetic moments of both nucleons and electrons are investigated in relativistic mean field calculations for a $β$-equilibrium system. Since neutrons are fully spin polarized in a large field, generally speaking, the proton fraction can never exceed the field free case. An extremely strong magnetic field may lead to a pure neutron matter instead of a proton-rich matter.

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arXiv2002

Bound states of anti-nucleons in finite nuclei

We study the bound states of anti-nucleons emerging from the lower continuum in finite nuclei within the relativistic Hartree approach including the contributions of the Dirac sea to the source terms of the meson fields. The Dirac equation is reduced to two Schrödinger-equivalent equations for the nucleon and the anti-nucleon respectively. These two equations are solved simultaneously in an iteration procedure. Numerical results show that the bound levels of anti-nucleons vary drastically when the vacuum contributions are taken into account.

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arXiv2000

Vacuum discharge as a possible source of gamma-ray bursts

We propose that spontaneous particle--anti-particle pair creations from the discharged vacuum caused by the strong interactions in dense matter are major sources of $γ$-ray bursts. Two neutron star collisions or black hole-neutron star mergers at cosmological distance could produce a compact object with its density exceeding the critical density for pair creations. The emitted anti-particles annihilate with corresponding particles at the ambient medium. This releases a large amount of energy. We discuss the spontaneous $p\bar{p}$ pair creations within two neutron star collision and estimate the exploded energy from $p\bar{p}$ annihilation processes. The total energy could be around $10^{51} - 10^{53}$ erg depending on the impact parameter of colliding neutron stars. This value fits well into the range of the initial energy of the most energetic $γ$-ray bursts.

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arXiv1999

Relativistic Hartree approach including both positive- and negative-energy bound states

We develop a relativistic model to describe the bound states of positive energy and negative energy in finite nuclei at the same time. Instead of searching for the negative-energy solution of the nucleon's Dirac equation, we solve the Dirac equations for the nucleon and the anti-nucleon simultaneously. The single-particle energies of negative-energy nucleons are obtained through changing the sign of the single-particle energies of positive-energy anti-nucleons. The contributions of the Dirac sea to the source terms of the meson fields are evaluated by means of the derivative expansion up to the leading derivative order for the one-meson loop and one-nucleon loop. After refitting the parameters of the model to the properties of spherical nuclei, the results of positive-energy sector are similar to that calculated within the commonly used relativistic mean field theory under the no-sea approximation. However, the bound levels of negative-energy nucleons vary drastically when the vacuum contributions are taken into account. It implies that the negative-energy spectra deserve a sensitive probe to the effective interactions in addition to the positive-energy spectra.

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arXiv1998

Microscopic Models for Ultrarelativistic Heavy Ion Collisions

In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended collision term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab}< 100$ MeV/nucleon up to $E_{lab}> 200$ GeV/nucleon, allowing for a consistent calculation of excitation functions from the intermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.

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