Effective Nucleon Masses in Symmetric and Asymmetric Nuclear Matter

The momentum and isospin dependence of the in-medium nucleon mass are studied. Two definitions of the effective mass, i.e., the Dirac mass $m_D^{*}$ and the nonrelativistic mass $m_{NR}^{*}$ which parametrizes the energy spectrum, are compared. Both masses are determined from relativistic Dirac-Brueckner-Hartree-Fock calculations. The nonrelativistic mass shows a distinct peak around the Fermi momentum. The proton-neutron mass splitting in isospin asymmetric matter is $m_{D,n}^{*}<m_{D,p}^{*}$ and opposite for the nonrelativistic mass, i.e., $m_{NR,n}^{*}>m_{NR,p}^{*}$, which is consistent with nonrelativistic approaches.

Figure 1

The effective mass in isospin symmetric nuclear matter as a function of the momentum $k=|\mathbf{k}|$ at different densities.

Figure 2

The effective mass in isospin symmetric nuclear matter at $k=|\mathbf{k}|=k_F$ as a function of the Fermi momentum $k_F$.

Figure 3

Neutron effective mass as a function of the momentum $k=|\mathbf{k}|$ for various values of the asymmetry parameter $\beta$ at fixed nuclear density $n_B=0.166{\mathrm{fm}}^{-3}$.

Figure 4

Neutron effective mass obtained in the RMF approximation as a function of the momentum $k=|\mathbf{k}|$ at fixed nuclear density $n_B=0.166{\mathrm{fm}}^{-3}$.