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arXiv 2209.00766nucl-thastro-ph.HEhep-ph
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受中子星约束的全息冷致密物质

Holographic cold dense matter constrained by neutron stars

Lin Zhang, Mei Huang

摘要:

在Einstein-Maxwell-Schwarzon(EMD)系统框架下,采用全息QCD模型,对物质部分采用改进的Karch-Katz-Son-Stephanov(KKSS)作用量,研究了中子星内部冷密物质的物态方程.这种在EMD $+$ KKSS框架中描述全息核物质的方法与用DBI作用量和CS项描述全息核物质的方法不同。结合Hebeler-Lattimer-Pethick-Schwenk(HLPS)中间状态方程,构造了中子星内部的混合状态方程.得到的混合EoS位于低密度手征有效理论、高密度微扰QCD以及它们之间的多方插值所定义的范围内,并受到天体物理观测的约束。声速的平方在$2-5$乘以饱和重子数密度的区域中达到大于$0.8$的最大值,并且在重子密度高的区域中接近共形极限。中子星的质量-半径关系和潮汐形变与天体物理测量结果一致。中子星可能的最大质量约为$2.5 M_{\odot}$,半径约为$12 \mathrm{km}$。注意到在质量-半径关系中,全息夸克物质分支总是不稳定的,而全息核物质可以产生稳定的分支。这些结果表明,即使在NS的核心,物质仍然处于限制阶段,夸克物质是不受欢迎的。

英文摘要:

The equation of state (EoS) for cold dense matter inside neutron stars is investigated by using holographic QCD models in the framework of the Einstein-Maxwell-dilaton (EMD) system and the improved Karch-Katz-Son-Stephanov (KKSS) action for matter part. This method of describing holographic nuclear matter in the EMD$+$KKSS framework is different from that by using the Dirac-Born-Infeld (DBI) action and the Chern-Simons (CS) terms. Combining with the Hebeler-Lattimer-Pethick-Schwenk (HLPS) intermediate equation of state (EoS), the hybrid EoS inside the neutron stars is constructed. The obtained hybrid EoS is located in the range that is defined by the low-density chiral effective theory, the high-density perturbative QCD, and the polytropic interpolations between them, and is constrained by the astrophysics observations. The square of the sound velocity reaches a maximum value larger than $0.8$ in the region of $2-5$ times the saturation baryon number density and approaches the conformal limit at the high baryon density range. The mass-radius relation and the tidal deformability of the neutron stars are in agreement with astrophysical measurements. The possible maximum mass for the neutron star is about $2.5 M_{\odot}$ and the radius is about $12 \mathrm{km}$ then. It is noticed that the holographic quark matter branch in the mass-radius relation is always unstable and the holographic nuclear matter can produce a stable branch. These results indicate that even in the core of the NS, the matter is still in the confinement phase and the quark matter is not favored.

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