Relativistic hypernuclear compact stars with calibrated equations of state

Abstract

Within the covariant density functional theory of hypernuclear matter we build a series of equations of state for hypernuclear compact stars, by calibrating the coupling constants of the Ξ-hyperon to the experimental binding energy of the single-Ξ hypernuclei 15 Ξ − C and 12 Ξ − Be. Coupling constants of the Λ-hyperon to nucleons have been calibrated on a vast collection of experimental data on single Λ-hypernuclei and we employ those values. Uncertainties on the couplings of the Σ-hyperon to nuclear matter, due to lack of experimental data, are accounted for by allowing for a wide variation of the well depth of Σ at rest in symmetric saturated nuclear matter. To account for uncertainties in the nucleonic sector at densities much larger than n 0 , a rich collection of parametrizations is employed, some of them in agreement with existing constraints from nuclear physics and astrophysics. Neutron star properties are investigated with all these calibrated equations of state. The effects of the presence of hyperons on the radius, on the tidal deformability, on the moment of inertia, and on the nucleonic direct Urca process are discussed. The sensitivity of the hyperonic direct Urca processes to uncertainties in the nucleonic and hyperonic sectors is also addressed. It is shown that the relative variations of the radius, tidal deformability and moment of inertia from the values that characterize purely nucleonic stars are linearly correlated with the strangeness fraction. The maximum radius deviation, obtained for most massive neutron stars, is ≈ 10%. The reduction of the maximum mass, triggered by nucleation of strangeness, is estimated at ≈ 15 − 20%, out of which 5% comes from insufficient information on the Σ-hyperon interactions. A total of 44 calibrated hyperonic equations of state are published as Supplemental Material.

Nuclear Physics and Astrophysics Constraints on the High Density Matter Equation of State

“…At higher densities in cold stars, hyperons appear naturally (due to Pauli blocking), when their chemical potentials exceed their effective masses and the strangeness non-conserving weak processes become possible [7][8][9][10][11]. Different models vary in predictions of the threshold densities for appearance of hyperons, which depend on hyperon couplings and the consequent hyperon binding energies [12]. At higher temperatures, hyperons exist at all densities [11], and have to be accounted for in EoS models.…”

“…The data were adopted from [171]. The models are labeled by numbers: (1) [166], (2) [165], (3) [172], (4) [167], (5,15) [173], (6,7,13,14) [171], (8) [174], (9) [175], (10) [170], (11) [176], (12) [177], (16) [178], (17) [179], (18) [58,180], and (19,20) [181].…”

Anisotropic neutron stars with hyperons: implication of the recent nuclear matter data and observations of neutron stars

“…The recent reports on the role of hyperons and other exotics and how to deal with the "hyperon puzzle" can be found, e.g., in Refs. [57][58][59][60][61][62][63][64][65][66][67][68] and also see the references therein.…”

Properties of rotating neutron star in density-dependent relativistic mean-field models

“…Some additional degrees of freedom, hyprons, Kaon or a deconfined phase of quark matter can also be imposed. The possible appearance of such an exotic core significantly affects the properties of neutron stars [2][3][4][5][24][25][26][27][28]. In this study, the neutron star core is assumed to be composed of only neutron, proton, electron and muon as a beta stable matter.…”