Astronomy and Astrophysics Seminars

# Cosmological horizon and quadrupole formula in de Sitter background

## by Dr. Sk Jahanur Hoque (IMSc, Chennai, India.)

Tuesday, September 12, 2017 from to (Asia/Kolkata)
at DAA SEMINAR ( A269 )
TIFR
 Description One of the physical realizations 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 $\mathcal{J}^{+}$.