MG15 - Talk detail

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In this talk, we present the results of our investigation of possibility of resolving the Chronology Protection Problem due to the existence of closed time-like curves in Kerr-Newman black-holes using modified gravity theories, particularly in the Non-Commutative geometry inspired and f(R) modified theories. Based on arXiv:1803.06666 Description of the work: We first revisit and quantify the details of the causality violation in the Kerr-Newman space-time. We then show that the issue also extends onto two of the modified Kerr-Newman solutions: the Non-Commutative geometry inspired solution and the f(R)-Gravity modified solution. The geodesic connectivity of the causality violating region is discussed in both the scenarios and the existence of null geodesics that contain points from the region is demonstrated. We also explore the possibility of mechanisms present within the model that can prevent causality violation. It is shown that although in both the models the model parameters can be chosen such that the causality violating region is eliminated, the resolution in the f(R) case is not consistent with cosmological observations. In the case of non-commutative geometry inspired solution, we show that chronology protection can be ensured by choosing suitable values for the non-commutative parameter, thereby eliminating the causality violating region and the Cauchy horizon. As a corollary, ee also discuss the causal aspects of Kerr-Newman de Sitter/anti-de Sitter space-times.

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