Relativistic mean-field models with scaled hadron masses and couplings: Hyperons and maximum neutron star mass

Abstract

An equation of state of cold nuclear matter with an arbitrary isotopic composition is studied within a relativistic mean-field approach with hadron masses and coupling constants depending self-consistently on the scalar mean-field. All hadron masses decrease universally with the scalar field growth, whereas meson-nucleon coupling constants can vary differently. More specifically we focus on two modifications of the KVOR model studied previously. One extension of the model (KVORcut) demonstrates that the equation of state stiffens if the increase of the scalar-field magnitude with the density is bounded from above at some value for baryon densities above the saturation nuclear density. This can be realized if the nucleon vector-meson coupling constant changes rapidly as a function of the scalar field slightly above the desired value. The other version of the model (MKVOR) utilizes a smaller value of the nucleon effective mass at the nuclear saturation density and a saturation of the scalar field in the isospin asymmetric matter induced by a strong variation of the nucleon isovector-meson coupling constant as function of the scalar field. A possibility of hyperonization of the matter in neutron star interiors is incorporated. Our equations of state fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, direct Urca constraint, gravitational-baryon mass constraint for the pulsar J0737-3039B, and the constraint on the maximum mass of the neutron stars.

Influence of the stiffness of the equation of state and in-medium effects on the cooling of compact stars

“…Moreover, the rapid DU-like processes on the hyperons may occur. Although recently it was demonstrated [100,101] how these problems might be smoothened it would be important to include the hyperons in the cooling code.…”

On Manifestation of In-Medium Effects in Neutron Stars and Heavy-Ion Collisions

“…For more details, see discussion in [1,[6][7][8][9][10][11][12][13][14]. Most difficult is the ability to satisfy simultaneously the heavy-ion-collision flow and the maximum neutron-star mass constraints.…”

“…The problems were named the hyperon [15,16] and the ∆ [17,18] puzzles. These problems can be resolved in the RMF models with scaled hadron masses and couplings [9][10][11]14]. The model employed in [11,14] is a generalization of the NLW model with effective coupling constants g * mb = g mb χ mb (σ) and hadron masses m * i = m i Φ i (σ), which are functions of the σ field [8], i = {b, m}, where m = {σ, ω, ρ, φ} lists the included mesonic fields, b = {N, H, ∆} indicates a baryon (nucleon N = p, n; hyperon H = Λ, Σ, Ξ; and ∆ isobar).…”

“…[9][10][11]14] use models of two kinds, the KVORcut-based models, where one exploits the cut in ω sector choosing accordingly the η ω ( f ) dependence, and the MKVORcut-based models, where one exploits the cut in ρ sector choosing accordingly the η ρ ( f ) dependence. In KVORcut models without inclusion of hyperons, the ρ − condensate appears by the second-order phase transition and the influence of the ρ − condensation on the EoS is minor.…”

“…[10,46]. Calculation of the spin-parameters g = (g nn + g np )/2, g = (g nn − g np )/2 needs to incorporate the contribution in the NN interaction beyond the mean-field Hartree-level.…”