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arXiv 2107.13804gr-qc
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与位移对称标量场非形式耦合的恒星

Stars disformally coupled to a shift-symmetric scalar field

Tact Ikeda, Aya Iyonaga, Tsutomu Kobayashi

摘要:

我们研究静态和球对称恒星非正式耦合到一个标量场。假设标量场是平移对称的,因此与物质耦合的度规的共形因子和非形式因子仅依赖于标量场的动力学项。假设标量场线性依赖于时间,我们考虑一个一般的位移对称标量张量理论和一般形式的物质能量动量张量,允许各向异性的压力和热通量的径向方向。根据引力场方程和能量-动量张量如何在非形式变换下变换,这是一个自然的起点。通过考察流体静力学平衡方程在存在导数依赖的共形因子和非形式因子时的结构,我们证明了恒星表面的能量密度和切向压力必须为零.这个事实被用来证明恒星表面的非形式不变性,这在以前是微妙和不清楚的。然后,我们专注于移位对称k-本质非形式耦合到物质,并研究了内部和外部的度量函数和标量场的轮廓更详细。结果表明,该解存在两个分支,依赖于标量场的速度。讨论了外时空的非形式相关度规函数。

英文摘要:

We investigate static and spherically symmetric stars disformally coupled to a scalar field. The scalar field is assumed to be shift symmetric, and hence the conformal and disformal factors of the metric coupled to matter are dependent only on the kinetic term of the scalar field. Assuming that the scalar field is linearly dependent on time, we consider a general shift-symmetric scalar-tensor theory and a general form of the matter energy-momentum tensor that allows for the anisotropic pressure and the heat flux in the radial direction. This is a natural starting point in light of how the gravitational field equations and the energy-momentum tensor transform under a disformal transformation. By inspecting the structure of the hydrostatic equilibrium equation in the presence of the derivative-dependent conformal and disformal factors, we show that the energy density and tangential pressure must vanish at the surface of a star. This fact is used to prove the disformal invariance of the surface of a star, which was previously subtle and unclear. We then focus on the shift-symmetric k-essence disformally coupled to matter, and study the interior and exterior metric functions and scalar-field profile in more detail. It is found that there are two branches of the solution depending on the velocity of the scalar field. The disformally-related metric functions of the exterior spacetime are also discussed.

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