Do current astronomical observations exclude the existence of nonstrange quark stars?

摘要

As is pointed out in a recent work [Phys. Rev. Lett. 120, 222001 (2018)], quark matter may not be strange. Inspired by this argument, we use a new self-consistent mean field approximation method to study the equation of state of cold dense matter within the framework of the two-flavor NJL model. Then the mass-radius relationship of two-flavor pure quark stars is studied. In the new self-consistent mean field approximation method we introduced, there is a free parameter α, which reflects the weight of different interaction channels. In principle, α should be determined by experiments rather than the self-consistent mean field approximation itself. In this paper, thus, the influence of the variation of α on the critical chemical potential of chiral phase transition and the stiffness of the equation of state (EOS) are thoroughly explored. The stiffness of the EOS can be increased greatly to support a two-solar-mass pure quark star when α is greater than 0.9, because the contribution from the vector term is retained by the Fierz transformation. Our result is also within the constraints on the radius from the recent data analysis of the tidal deformability. This means that the current theoretical calculations and astronomical observations cannot rule out the possibility of a two-flavor pure quark star.