Browsing by Author "Luo, Ling-Wei"

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Equation-of-state of neutron stars with junction conditions in the Starobinsky model
(2018-01-01)
Feng, Wei-Xiang
;
Geng, Chao-Qiang
;
Kao, W. F.
;
Luo, Ling-Wei
;
物理研究所
We study the Starobinsky or R-2 model of f(R) = R + alpha R-2 for neutron stars with the structure equations represented by the coupled differential equations and the polytropic type of the matter equation-of-state (EoS). The junction conditions of f(R) gravity are used as the boundary conditions to match the Schwarzchild solution at the surface of the star. Based on these the conditions, we demonstrate that the coupled differential equations can be solved directly. In particular, from the dimensionless EoS (rho) over bar = (kp) over bar gamma with (k) over bar similar to 5.0 and gamma similar to 0.75 and the constraint of alpha less than or similar to 1.47722 x 10(7) m(2), we obtain the minimal mass of the NS to be around 1.44 M circle dot. In addition, if (k) over bar is larger than 5.0, the mass and radius of the NS would be smaller.
Stability of Einstein static state universe in the spatially flat branemodels
(2016-07-10)
Zhang, Kaituo
;
Wu, Puxun
;
Yu, Hongwei
;
Luo, Ling-Wei
;
物理研究所
With the assumption that a perfect fluid with a constant equation of state is the only energy component on the brane, we study the stability of Einstein static state solution under homogeneous and inhomogeneous scalar perturbations in both spatially flat Randall-Sundrum (RS) and Shtanov-Sahni (SS) braneworlds. We find that if the perfect fluid has a phantom-like property and the "Weyl fluid" originating from the projection of the bulk Weyl tensor onto the brane behaves like a radiation with positive energy density, the Einstein static state solution is stable in the SS braneworld, but unstable in the RS one. Furthermore, we demonstrate that the static state solution is also stable in the bulk with a timelike extra dimension. Thus, in the model where the extra dimension is timelike, our universe can stay at the Einstein static state past-eternally, which means that the big bang singularity might be resolved successfully by an emergent scenario. (C) 2016 The Authors. Published by Elsevier B.V.