标题： 各向异性压力对PSR J0740+6620中心方程的状态方程的影响：基于无量纲TOV方程的研究 显示英文标题

标题： Anisotropic pressure effect on central EOS of PSR J0740+6620 in the light of dimensionless TOV equation

摘要： 人们普遍认为中子星内部的压力是各向同性的。然而，强磁场或超流性表明压力各向异性可能是一种更现实的模型。我们基于两种流行的模型——BL 模型和H 模型推导了各向异性中子星的无量纲 TOV 方程，以研究各向异性的影响。与各向同性情况类似，最大质量 $M_{max}$和其对应的半径 $R_{Mmax}$也可以通过径向中心压力 $p_{rc}$和中心能量密度 $\varepsilon_{c}$的线性组合来表示，这与状态方程（EOS）无关。我们还发现，所得到的中心状态方程会随着 $\lambda_{BL}$（$\lambda_{H}$）的不同取值而变化，该参数控制着横向压力与径向压力之间差异的大小。 结合PSR J0740+6620的观测数据并与基于各向同性中子星提取的物态方程进行比较，在BL模型中，当$\lambda_{BL}$= 0.4 时，中心能量密度$\varepsilon_{c}$从 546 – 1056 MeV/fm$^{3}$变化到 510 – 1005 MeV/fm$^{3}$，而径向中心压力$p_{rc}$从 87 – 310 MeV/fm$^{3}$变化到 76 – 271 MeV/fm$^{3}$。 对于 \($\lambda_{BL}$= 2 \)，提取的 $\varepsilon_{c}$ 和 $p_{rc}$ 分别变为了 412–822 MeV/fm $^{3}$ 和 50–165 MeV/fm $^{3}$。 在H模型中，当$\lambda_{H}$= 0.4 时，提取的$\varepsilon_{c}$变为 626–1164 MeV/fm$^{3}$，提取的$p_{rc}$变为 104–409 MeV/fm$^{3}$。 对于 \($\lambda_{H}$= 2 \)，提取的 $\varepsilon_{c}$ 减少到 894–995 MeV/fm $^{3}$，提取的 $p_{rc}$ 变为 220–301 MeV/fm $^{3}$。 显示英文摘要

摘要： It is generally agreed upon that the pressure inside a neutron star is isotropic. However, a strong magnetic field or superfluidity suggests that the pressure anisotropy may be a more realistic model. We derived the dimensionless TOV equation for anisotropic neutron stars based on two popular models, namely the BL model and the H model, to investigate the effect of anisotropy. Similar to the isotropic case, the maximum mass $M_{max}$ and its corresponding radius $R_{Mmax}$ can also be expressed linearly by a combination of radial central pressure $p_{rc}$ and central energy density $\varepsilon_{c}$, which is insensitive to the equation of state (EOS). We also found that the obtained central EOS would change with different values of $\lambda_{BL}$ ($\lambda_{H}$), which controls the magnitude of the difference between the transverse pressure and the radial pressure. Combining with observational data of PSR J0740+6620 and comparing to the extracted EOS based on isotropic neutron star, it is shown that in the BL model, for $\lambda_{BL}$ = 0.4, the extracted central energy density $\varepsilon_{c}$ changed from 546 -- 1056 MeV/fm$^{3}$ to 510 -- 1005 MeV/fm$^{3}$, and the extracted radial central pressure $p_{rc}$ changed from 87 -- 310 MeV/fm$^{3}$ to 76 -- 271 MeV/fm$^{3}$. For $\lambda_{BL}$ = 2, the extracted $\varepsilon_{c}$ and $p_{rc}$ changed to 412 -- 822 MeV/fm$^{3}$ and 50 -- 165 MeV/fm$^{3}$, respectively. In the H model, for $\lambda_{H}$ = 0.4, the extracted $\varepsilon_{c}$ changed to 626 -- 1164 MeV/fm$^{3}$, and the extracted $p_{rc}$ changed to 104 -- 409 MeV/fm$^{3}$. For $\lambda_{H}$ = 2, the extracted $\varepsilon_{c}$ decreased to 894 -- 995 MeV/fm$^{3}$, and the extracted $p_{rc}$ changed to 220 -- 301 MeV/fm$^{3}$.