Nonrelativistic nucleon effective masses in nuclear matter: BHF versus RHF

Abstract

The density and isospin dependences of the nonrelativistic nucleon effective mass ($m^{\ast }$) are studied, which is a measure of the nonlocality of the single particle (s.p.) potential. We decouple it further into the so called k-mass ($m_k^{\ast }$, i.e., the nonlocality in space) and E-mass ($m_E^{\ast }$, i.e., the nonlocality in time). Both masses are determined and compared from the latest versions of the nonrelativistic Brueckner-Hartree Fock (BHF) model and the relativistic Hartree-Fock (RHF) model. The latter are achieved based on the corresponding Schrödinger equivalent s.p. potential in a relativistic framework. We demonstrate the origins of different effective masses and discuss also their neutron-proton splitting in the asymmetric matter in different models. We find that the neutron-proton splittings of both the k-mass and the E-mass have the same asymmetry dependences at considered densities, namely $m_{k,n}^{\ast }>m_{k,p}^{\ast }$ and $m_{E,p}^{\ast }>m_{E,n}^{\ast }$. However, the resulting splittings of nucleon effective masses could have different asymmetry dependences in the two models, because they could be dominated either by that of the k-mass (then we have $m_n^{\ast }>m_p^{\ast }$ in the BHF model) or by that of the E-mass (then we have $m_p^{\ast }>m_n^{\ast }$ in the RHF model).

4 pages, 5 figures, 1 table, PHYSICAL REVIEW C (2016) accepted