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11.00 am, Seminar Hall Cosmological horizon and quadrupole formula in de Sitter background Sk Jahanur Hoque Institute of Mathematical Sciences, Chennai. 30-08-17 Abstract One of the physical realisations of gravitational waves is that they carry energy. Though there is no gauge invariant local definition of gravitational stress energy tensor, in the special context of two widely separated scales, Isaacson defined an effective gravitational stress tensor for the ripples. Energy computed from effective stress tensor is well understood for weak gravitational waves in Minkowski background. In de Sitter background space-like character of future null infinity $\mathcal{J}^{+}$, makes the definition of energy subtle. A spatially compact source in de Sitter background also provides a distinguished null hypersurface, its cosmological horizon, $\mathcal{H}^{+}$. In this talk I will discuss how Isaacson prescription can be adopted to compute energy flux in de Sitter background. Energy flux computed using effective stress tensor can be evaluated at $\mathcal{H}^{+}$ and matches with that computed at $\mathcal{J}^{+}$.To get an order of estimate I will also discuss power radiated by a binary system in de Sitter background.
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