Neutron stars in scalar-tensor theories: Analytic scalar charges and universal relations
Neutron stars in scalar-tensor theories: Analytic scalar charges and universal relations
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标量张量理论中的中子星：解析标量电荷和普遍关系
DOI：
10.1103/physrevd.104.044017
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发表时间：
2021
影响因子：
5
通讯作者：
Stepniczka, Michael
中科院分区：
文献类型：
--
作者：
Yagi, Kent;Stepniczka, Michael
中子星密度大，引力场强，是探测广义相对论的理想天体物理源。例如，双星脉冲星和引力波的观测对某些标量张量理论施加了严格的限制，在这些理论中，无质量的标量场通过物质与度规耦合。在这样的标量-张量理论中，中子星的一个显著现象是自发标量，即使物质-标量耦合在远离中子星的地方渐近消失，归一化标量电荷仍然保持秩序统一。虽然大多数关于中子星标量化的工作都集中在数值分析上，但本文的目的是从解析的角度推导出精确的标量电荷。为了实现这一点，我们考虑了一个简单的Tolman VII形式的能量密度分布，并在弱场展开中工作。我们将按顺序求解修正的Tolman-Oppenheimer-Volkoff方程，并应用Padé恢复法来考虑高阶效应。我们发现，我们的解析标量电荷(根据恒星的致密性)很好地模拟了数值计算的结果。我们还发现了标量电荷和恒星结合能之间的准普适关系，这种关系对基本的状态方程不敏感。托尔曼7号星和恒定密度星的解析标量电荷的比较从数学上支持了这一准宇宙关系。这里的分析结果提供了物理激励的、随时可以使用的标量电荷的精确表达式。
Neutron stars are ideal astrophysical sources to probe general relativity due to their large compactnesses and strong gravitational fields. For example, binary pulsar and gravitational wave observations have placed stringent bounds on certain scalar-tensor theories in which a massless scalar field is coupled to the metric through matter. A remarkable phenomenon of neutron stars in such scalar-tensor theories is spontaneous scalarization, where a normalized scalar charge remains of order unity even if the matter-scalar coupling vanishes asymptotically far from the neutron star. While most works on scalarization of neutron stars focus on numerical analysis, this paper aims to derive accurate scalar charges analytically. To achieve this, we consider a simple energy density profile of the Tolman VII form and work in a weak-field expansion. We solve the modified Tolman-Oppenheimer-Volkoff equations order by order and apply a Padé resummation to account for higher order effects. We find that our analytic scalar charges (in terms of the stellar compactness) beautifully model those computed numerically. We also find a quasiuniversal relation between the scalar charge and stellar binding energy that is insensitive to the underlying equations of state. A comparison of analytic scalar charges for Tolman VII and constant density stars mathematically supports this quasiuniversal relation. The analytic results found here provide physically motivated, ready to use accurate expressions for scalar charges.
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