Effects of Isoscalar- and Isovector-scalar Meson Mixing on Neutron Star Structure

Abstract

Based on the accurately calibrated interaction FSUGold, we show that including isovector-scalar δ meson and its coupling to isoscalar-scalar σ meson in the relativistic mean-field (RMF) model can soften the symmetry energy E sym(n) at intermediate densities while stiffening the E sym(n) at high densities. We find this new RMF model can be simultaneously compatible with (1) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions; (2) the neutron skin thickness of 208Pb from the PREX-II experiment; (3) the largest mass of a neutron star (NS) reported so far from PSR J0740+6620; (4) the limit of Λ1.4 ≤ 580 for the dimensionless tidal deformability of the canonical 1.4 M ⊙ NS from the gravitational-wave signal GW170817; (5) the mass–radius relation of PSR J0030+0451 and PSR J0740+6620 measured by NICER. The new model thus removes the tension between PREX-II and GW170817 observed in the conventional RMF model.

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“…For the study of isospin asymmetric matter only vector-isovector ρ field was used during the initial development of this model. However, as has been emphasized in various studies, the scalar-isovector meson δ plays a significant role in the study of isospin asymmetric effects and hence, has been included in the current work [44][45][46]. Finite baryon density and temperature of the medium lead to the modification in the properties of these constituent quarks and hence the baryons.…”