报告人：Mohammad Sabir Ali博士后（印度科学教育与研究所）

题 目:Stationary black holes and stars in the Brans-Dicke theory for a positive cosmological constant revisited

时 间：2023年4月12日（周三）16:00

地 点：理工楼1226

联系人：刘玉孝

报告摘要:

It has been shown a few years back that for a stationary regular black hole or star solution in the Brans-Dicke theory with a positive cosmological constant endowed with a de Sitter or cosmological event horizon in the asymptotic region, not only there exists no nontrivial field configurations, but also the inverse Brans-Dicke parameter must be vanishing. The assumption of the existence of the cosmological horizon was crucial for this proof. However, since the Brans-Dicke field couples directly to the cosmological constant-term in the energy-momentum tensor as well as it acts as a source in the equation of motion of the Brans-Dicke field, it seems reasonable to ask: can Brans-Dicke field become strong instead and screen the effect of cosmological constant, at very large scales, so that the asymptotic de Sitter structure is replaced by some alternative, yet still acceptable boundary condition? In this work we analytically argue that no such alternative exists, as long as spacetime is assumed to be free of any naked curvature singularity. We further support this result by providing explicit numerical computations. Thus we conclude that in the presence of a positive cosmological constant, irrespective of whether the asymptotic de Sitter boundary condition is imposed or not, a regular stationary black hole or even a star solution in the Brans-Dicke theory always necessitates the inverse Brans-Dicke parameter to be vanishing and thereby reducing the theory to general relativity. The qualitative differences of this result with that of the standard no hair theorems are also pointed out.

报告人简介:

Md Sabir Ali obtained his masters degree in Theoretical High Energy Physics from the Aligarh Muslim University (2014) and the Doctorate (Ph.D.) degree (2020) from the Centre for Theoretical Physics at Jamia Millia Islamia. His doctorcal thesis works were based on the properties of the black holes including the lensing phenomena, the thermodynamics and the shdow properties in asymptotically (anti)-de Sitter spacetime. He did his first postdoctor from Indian Institute of Technology Ropar for two years. He then got the SERB-National Postdoctor Fellowship from the Department of Science and Technology, Government of India and worked at the Indian Institute of Scinece Education and Research Kolkata. Recently, he joined Lanzhou University as a postdoctoral researcher at the School of Physical Science and Technology. His work mainly focuses on the thermal and optical properties of the black holes. He is also interested to work on Quasinormal modes and the stability properties of the black holes. His few reseacrh works include the quantum field theoretaspects in curved spacetime.