Deformation effect on the center-of-mass correction energy in nuclei ranging from Oxygen to Calcium

The microscopic center-of-mass (c.m.) correction energies for nuclei ranging from Oxygen to Calcium are systematically calculated by both spherical and axially deformed relativistic mean-field (RMF) models with the effective interaction PK1. The microscopic c.m. correction energies strongly depend on the isospin as well as deformation and deviate from the phenomenological ones. The deformation effect is discussed in detail by comparing the deformed with the spherical RMF calculation. It is found that the direct and exchange terms of the c.m. correction energies are strongly correlated with the density distribution of nuclei and are suppressed in the deformed case.Comment: 7 pages, 3 figures, accepted by Chin.Phys.Let

Deformation effect on the center-of-mass correction energy in nuclei ranging from Oxygen to Calcium

The microscopic center-of-mass (c.m.) correction energies for nuclei ranging from Oxygen to Calcium are systematically calculated by both spherical and axially deformed relativistic mean-field (RMF) models with the effective interaction PK1. The microscopic c.m. correction energies strongly depend on the isospin as well as deformation and deviate from the phenomenological ones. The deformation effect is discussed in detail by comparing the deformed with the spherical RMF calculation. It is found that the direct and exchange terms of the c.m. correction energies are strongly correlated with the density distribution of nuclei and are suppressed in the deformed case.Comment: 7 pages, 3 figures, accepted by Chin.Phys.Let

Relativistic mean-field approximation with density-dependent screening meson masses in nuclear matter

The Debye screening masses of the $\sigma$, $\omega$ and neutral $\rho$ mesons and the photon are calculated in the relativistic mean-field approximation. As the density of the nucleon increases, all the screening masses of mesons increase. It shows a different result with Brown-Rho scaling, which implies a reduction in the mass of all the mesons in the nuclear matter except the pion. Replacing the masses of the mesons with their corresponding screening masses in Walecka-1 model, five saturation properties of the nuclear matter are fixed reasonably, and then a density-dependent relativistic mean-field model is proposed without introducing the non-linear self-coupling terms of mesons.Comment: 14 pages, 3 figures, REVTEX4, Accepted for publication in Int. J. Mod. Phys.

Effective photon mass in nuclear matter and finite nuclei

Electromagnetic field in nuclear matter and nuclei are studied. In the nuclear matter, because the expectation value of the electric charge density operator is not zero, different in vacuum, the U(1) local gauge symmetry of electric charge is spontaneously broken, and consequently, the photon gains an effective mass through the Higgs mechanism. An alternative way to study the effective mass of photon is to calculate the self-energy of photon perturbatively. It shows that the effective mass of photon is about $5.42MeV$ in the symmetric nuclear matter at the saturation density $\rho_0 = 0.16fm^{-3}$ and about $2.0MeV$ at the surface of ${}^{238}U$. It seems that the two-body decay of a massive photon causes the sharp lines of electron-positron pairs in the low energy heavy ion collision experiments of ${}^{238}U+{}^{232}Th$ .Comment: 10 pages, 2 figures, 1 table, REVTEX4, submitted to Int. J. Mod. Phys.

The Temporal and Spectral Characteristics of "Fast Rise and Exponential Decay" Gamma-Ray Burst Pulses

In this paper we have analyzed the temporal and spectral behavior of 52 Fast Rise and Exponential Decay (FRED) pulses in 48 long-duration gamma-ray bursts (GRBs) observed by the CGRO/BATSE, using a pulse model with two shape parameters and the Band model with three shape parameters, respectively. It is found that these FRED pulses are distinguished both temporally and spectrally from those in long-lag pulses. Different from these long-lag pulses only one parameter pair indicates an evident correlation among the five parameters, which suggests that at least $\sim$4 parameters are needed to model burst temporal and spectral behavior. In addition, our studies reveal that these FRED pulses have correlated properties: (i) long-duration pulses have harder spectra and are less luminous than short-duration pulses; (ii) the more asymmetric the pulses are the steeper the evolutionary curves of the peak energy ($E_{p}$) in the $\nu f_{\nu}$ spectrum within pulse decay phase are. Our statistical results give some constrains on the current GRB models.Comment: 18 pages, 7 figures, accepted for publication in the Astrophysical Journa