Motivated by a recent report by Biwas and Bose (Phys Rev D 99:104002, 2019) that the observations of GW170817 to constrain the extent of pressure anisotropy in neutron stars within Bower–Liang anisotropic model, we systematically study the effects of anisotropic pressure on properties of the neutron stars with hyperons. The equation of state is calculated using the relativistic mean-field model with a BSP parameter set to determine nucleonic coupling constants and by using SU(6) and hyperon potential depths to determine hyperonic coupling constants. We investigate three models of anisotropic pressure known in literature namely Bowers and Liang (Astrophys J 88:657, 1974), Horvat et al. (Class Quant Grav 28:025009, 2011), and Cosenza et al. (J Math Phys (NY) 22:118, 1981). The reliability of the equation of state used is checked by comparing the parameters of the corresponding EOS to recent experimental data. The mass–radius, moment of inertia, and tidal deformability results of Bowers–Liang, Horvat et al., and Cosenza et al. anisotropic models are compared to the corresponding recent results extracted from the analysis of some NS observation data. We have found that the radii predicted by anisotropic NS are sensitive to the anisotropic model used and the results obtained by using the model proposed by Horvat et al. with anisotropic free parameter $$\varUpsilon ~\approx -$$Υ≈- 1.15 are relative compatible with all taken constraints.
The role of scalar boson exchange as a mediator of the fermionic dark particle interaction and the mass of dark particle on the bulk properties of fermionic dark stars including their moment of inertia and tidal deformability are studied. We have found that the role of the attractive nature of the scalar boson exchange and the fermionic dark particle mass can control the stiffness of the fermionic dark star equation of state. By increasing the strength of scalar boson coupling, the fermionic dark star becomes more compact. As a consequence, if scalar boson exchange contribution is included the compactness of a dark star can exceed C=0.22. We also compare the fermionic dark stars moment of inertia and tidal deformability to those of neutron stars (with and without hyperons in neutron star core) predicted by relativistic mean field model. It is evidence that the properties of both types of stars are quite different. We also have found that the universal I-Love relation in fermionic dark stars is not affected by scalar boson exchange contribution and the fermionic dark particle mass. Possible observations of fermionic dark stars are also discussed.
Dark star is a hypothetical stellar compact object composed of dark particles which clumped together due to self-interaction among dark particles. Tidal Love numbers from binary stars are potential observables for studying the internal structure of the stars. The Tidal Love numbers can be deduced from the gravitational wave of the coalescence or inspiral of binary stars. The ground base interferometer can measure the corresponding gravitational wave. In this work, we study the equation of state, mass-radius relation, electric, magnetic and surficial tidal love numbers of dark stars. We obtain that Tidal Love numbers are not too sensitive to study the role of scalar boson exchange and the impact of the mass of the dark particle in dark matter equation of state.
In this paper, we employ one variant of the Generalized Uncertainty Principle (GUP) model, i.e., the Kempf–Mangano–Mann (KMM) model, and discuss the impact of GUP on the EoS of nuclear and neutron star matter based on the relativistic mean field (RMF) model. We input the result in the Serrano–Liška (SL) gravity theory to discuss the corresponding Neutron Star (NS) properties. We have shown that the upper bound for the GUP parameter from nuclear matter properties is $$\beta \le 2\times 10^{-7}$$ β ≤ 2 × 10 - 7 MeV$$^{-2}$$ - 2 . If we used this $$\beta $$ β upper bound to calculate NS matter, and considering SL parameter $${\tilde{c}}$$ c ~ as an independent parameter, we have found that the upper bound for the SL parameter, which modifies the Einstein field equation, is $${\tilde{c}} \le 10^7$$ c ~ ≤ 10 7 m$$^2$$ 2 . This beta upper bound is determined by considering the anisotropy magnitude smaller than the pressure magnitude. By employing $$\beta =2\times 10^{-7}$$ β = 2 × 10 - 7 MeV$$^{-2}$$ - 2 and $${\tilde{c}} = 10^7$$ c ~ = 10 7 m$$^2$$ 2 , we obtain the mass–radius relation that satisfies NICER data for both PSR J0740+6620 (whose mass is $$\sim 2.1M_\odot $$ ∼ 2.1 M ⊙ ) and PSR J0030+0451 ($$M\sim 1.4M_\odot $$ M ∼ 1.4 M ⊙ ). Our GUP parameter upper bound perfectly matches the constraint from $$^{87}$$ 87 Rb cold-atom-recoil experiment. If we consider that the same strength from the additional logarithmic term in the entropy from both GUP and SL model are dependent, for $$\beta < 2\times 10^{-7}$$ β < 2 × 10 - 7 MeV$$^{-2}$$ - 2 , it is clear that SL parameter lower bound is $${\tilde{c}} > -16\times 10^{-34}$$ c ~ > - 16 × 10 - 34 m$$^2$$ 2 . The magnitude of this bound is $$10^{-40}$$ 10 - 40 smaller than the upper bound magnitude of SL parameter considering as independent parameter i.e., $${\tilde{c}} \le 10^7$$ c ~ ≤ 10 7 m$$^2$$ 2 .
It has been reported that there is a discrepancy of 4σ in the neutron lifetime measurement with two methods, i.e., the trap method (measuring the number of neutrons remaining in the various time intervals) and beam method (measuring the number of protons formed from regulated neutrons currents). Fornal and Grinstein (2019) proposed that the possibility neutrons decay into the dark matter can explain this discrepancy. In this study, the author asses the consequence of the proposal by studying the impact on neutron stars with Hyperon. Based on our numerical calculation we found that dark matter may be present in the core of a neutron star because it only appears at very high densities, and the population is negligible with a maximum population of about 0.1%
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