arXiv 2101.030342021-01gr-qchep-th

Einstein-Maxwell标量理论中的慢转黑洞

Slowly rotating black holes in the Einstein-Maxwell-scalar theory

Jianhui Qiu

备注：: 17 pages, 11 figures
DOI：: 10.1140/epjc/s10052-021-09890-3

摘要：

在对一般Einstein-Maxwell标量理论进行分类的基础上，提出了一种新的Einstein-Maxwell标量理论，研究了慢旋转黑洞解.计算了该黑洞的旋磁比，它随第二自由参数$β$的增大而增大，随参数$γ\equiv \frac{2 α^{2}}{1+α^2}$的增大而减小.在Einstein-Maxwell-Maxwell（EMD）理论中，参数$β$消失，但控制Maxwell场和Maxwell场之间耦合强度的自由参数$α$保留。旋磁比总是小于$2$，这是Kerr-Newman（KN）黑洞和狄拉克电子的著名值。标量毛减少了狄拉克理论中的磁偶极矩，导致旋磁比下降。然而，我们发现，在爱因斯坦-麦克斯韦标量理论中，通过同时增加$β$和荷质比$Q/M$，可以实现2的旋磁比（回想一下，KN黑洞的旋磁比与$Q/M$无关）。同样的情况也适用于局部非旋转观测者的角速度。此外，我们还分析了用荷质比对圆轨道的周期修正，以及对最内层稳定圆轨道半径的修正。结果表明，$β$的校正值增大，而$Q/M$的校正值减小。最后，研究了总辐射效率，当考虑旋转效应时，总辐射效率为零。

英文摘要：

We investigate a slowly rotating black hole solution in a novel Einstein-Maxwell-scalar theory, which is prompted by the classification of general Einstein-Maxwell-scalar theories. The gyromagnetic ratio of this black hole is calculated, and it increases as the second free parameter $β$ increases, but decreases with the increasing parameter $γ\equiv \frac{2 α^{2}}{1+α^2}$. In the Einstein-Maxwell-dilaton (EMD) theory, the parameter $β$ vanishes, but the free parameter $α$ governing the strength of the coupling between the dilaton and the Maxwell field remains. The gyromagnetic ratio is always less than $2$, the well-known value for a Kerr-Newman (KN) black hole as well as for a Dirac electron. Scalar hairs reduce the magnetic dipole moment in dilaton theory, resulting in a drop in the gyromagnetic ratio. However, we find that the gyromagnetic ratio of two can be realized in this Einstein-Maxwell-scalar theory by increasing $β$ and the charge-to-mass ratio $Q/M$ simultaneously (recall that the gyromagnetic ratio of KN black holes is independent of $Q/M$). The same situation also applies to the angular velocity of a locally non-rotating observer. Moreover, we analyze the period correction for circular orbits in terms of charge-to-mass ratio, as well as the correction of the radius of the innermost stable circular orbits. It is found the correction increases with $β$ but decreases with $Q/M$. Finally, the total radiative efficiency is investigated, and it can vanish once the effect of rotation is considered.

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摘要：

英文摘要：

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