Quadrupole formulae with cosmological constant: comparison

Abstract

We consider three different approaches (by Ashtekar, Bonga and Kesavan; Hoque and Virmani; and Dobkowski-Ry\l{}ko and Lewandowski) to investigate gravitational radiation produced by time changing matter source in de Sitter spacetime. All of them lead to generalizations of the quadrupole formula, however, due to different gauge conditions and choices of the hypersurfaces, across which the energy flux is computed, it is nontrivial to see that they all coincide, as one would expect from the symplectic theory. Each of the expressions for the radiated energy in the form of gravitational waves is expressed in terms of the mass and pressure quadrupole moments and written explicitly up to the linear order in $\sqrt{\Lambda}$, or equvalently in Hubble parameter $H$. It is shown that up to the first order all three of the generalizations of the quadrupole formula agree.