引力散射产生的标量场的轨道angular momentum
Orbital angular momentum of scalar field generated by gravitational scatterings
摘要：
人们一直期望通过天文观测来探测电磁波的轨道角动量，这可能会给我们对天体物理学的新认识。以前的工作指出了旋转黑洞通过引力散射可以产生电磁波的轨道角动量的可能性，通过观测它们可以测量黑洞的自旋参数。然而，电磁波的轨道角动量是如何通过引力散射产生的机制还没有得到充分的阐明。为了从引力透镜效应的角度来理解它，本文考虑一个辐射出实无质量标量场的球面波的辐射源，并借助于几何光学近似，研究了黑洞对球面波的引力散射对标量波的变形.我们证明了旋转黑洞引起的坐标系拖曳不是产生标量波轨道角动量的必要条件。然而，只有当黑洞旋转时，它的平行于图像方向余弦的分量才会出现。
英文摘要：
It has been expected that astronomical observations to detect the orbital angular momenta of electromagnetic waves may give us a new insight into astrophysics. Previous works pointed out the possibility that a rotating black hole can produce orbital angular momenta of electromagnetic waves through gravitational scattering, and the spin parameter of the black hole can be measured by observing them. However, the mechanism how the orbital angular momentum of the electromagnetic wave is generated by the gravitational scattering has not been clarified sufficiently. In this paper, in order to understand it from a point of view of gravitational lensing effects, we consider an emitter which radiates a spherical wave of the real massless scalar field and study the deformation of the scalar wave by the gravitational scattering due to a black hole by invoking the geometrical optics approximation. We show that the frame dragging caused by the rotating black hole is not a necessary condition for generating the orbital angular momentum of the scalar wave. However, its components parallel to the direction cosines of images appear only if the black hole is rotating.
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