1 Hyperonic matter in neutron star P. K. Sahu a∗ and A. Ohnishi a a Division of Physics, Hokkaido university, Sapporo 060-0810, Japan We discuss appearance and role of hyperons in neutron star matter with recent compiled nuclear equation of state from heavy-ion collisions. We also discuss different hyperon cou- plings from analysis of various experimental data on hypernuclei. We find that the sigma baryons do not appear in the neutron star matter, when it experiences a strong repulsive potential. However, the change in maximum mass of the neutron stars is insignificant against the different hyperon couplings. 1. INTRODUCTION In spite of more than two decades of work, the nuclear equation of state (EOS), which is required in calculation of neutron star properties is uncertain due to various reasons. The EOS at high baryon densities is one source of uncertainties, because it sensitively depends on short range nucleon-nucleon interaction. Furthermore, weak decay of neutrons into hyperons may be energetically allowed at high densities and the neutron matter may contains hyperons at such large baryon densities. If hyperons are likely to exist in high density matter, then it must be noted that the interaction of hyperons with other baryons is not well understood and the EOS is therefore uncertain. In this discussion, we use an extended version of the relativistic mean field model with momentum dependent forces, which are taken phenomenologically in the relativistic trans- port model in heavy-ion collisions [1]. The EOS was then derived by using momentum dependent constraints in the nuclear potentials [2]. We employ the same EOS in the neutron star calculation, where the composition of the star matter consists of lambdas, sigmas, cascades, neutrons, protons, electrons and muons. 2. NEUTRON STAR MATTER The EOS of neutron star matter is calculated in the frame work of the mean-field theory using covariant Lagrangian [3,4] given below. L =  i ¯ ψ i (iγ μ ∂ μ - m i + g σi σ + g ωi ω μ γ μ - g ρi ρ a μ γ μ T a )ψ i - 1 4 ω μν ω μν + 1 2 m 2 ω ω μ ω μ + 1 2 (∂ μ σ∂ μ σ - m 2 σ σ 2 ) - 1 4 ρ a μν ρ μν a + 1 2 m 2 ρ ρ a μ ρ μ a - 1 3 bm N (g σN σ) 3 - 1 4 c(g σN σ) 4 +  l ¯ ψ l (iγ μ ∂ μ - m l )ψ l . (1) * PKS was supported by the Japan Society for the Promotion of Science (ID No. P98357), Japan.