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arXiv 2007.03947gr-qcastro-ph.HEhep-th
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从观测到的喷流功率和辐射效率看Einstein-Maxwell介子-轴子引力的特征

Signatures of Einstein-Maxwell dilaton-axion gravity from the observed jet power and the radiative efficiency

Indrani Banerjee, Bhaswati Mandal, Soumitra SenGupta

摘要:

爱因斯坦-麦克斯韦介子-轴子(EMDA)引力产生于杂化弦论的低能有效作用量,并提供了一个简单的框架来探索相同的签名。从弦紧化的作用中继承下来的介子场和轴子场在暴胀宇宙学和解释目前宇宙的加速膨胀中有着有趣的结果。因此,在现有的天体物理观测中寻找这些场的足迹是值得的。由于爱因斯坦引力在高曲率域中被期望接受量子修正,黑洞的近视界区域似乎是测试这些偏离广义相对论的理想天体物理实验室。EMDA引力中精确的、稳态的和轴对称的黑洞解对应于带有介子荷的Kerr-Sen时空,而角动量来源于轴子场。来自吸积盘的弹道喷流和连续谱的峰值发射被认为是非常接近事件视界发射的,因此应该带有背景时空的印记。我们计算了克尔-森背景下连续谱的喷流功率和辐射效率,并与微类星体的相应观测结果进行了比较。我们的分析表明,与带有膨胀子电荷的克尔-森黑洞相比,克尔黑洞更受青睐。

英文摘要:

The Einstein-Maxwell dilaton-axion (EMDA) gravity arises in the low energy effective action of the heterotic string theory and provides a simple framework to explore the signatures of the same. The dilaton and the axion fields inherited in the action from string compactifications have interesting consequences in inflationary cosmology and in explaining the present accelerated expansion of the universe. It is therefore worthwhile to search for the footprints of these fields in the available astrophysical observations. Since Einstein gravity is expected to receive quantum corrections in the high curvature domain, the near horizon regime of black holes seems to be the ideal astrophysical laboratory to test these deviations from general relativity. Exact, stationary and axisymmetric black hole solution in EMDA gravity corresponds to the Kerr-Sen spacetime which carries dilaton charge, while the angular momentum is sourced by the axion field. The ballistic jets and the peak emission of the continuum spectrum from the accretion disk are believed to be launched very close to the event horizon and hence should bear the imprints of the background spacetime. We compute the jet power and the radiative efficiency derived from the continuum spectrum in the Kerr-Sen background and compare them with the corresponding observations of microquasars. Our analysis reveals that Kerr black holes are more favored compared to Kerr-Sen black holes with dilaton charges.

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