The current-type quadrupole moment and gravitational-wave mode $(\ell,m)=(2,1)$ of compact binary systems at the third post-Newtonian order

TL;DR

This paper computes the current quadrupole moment and gravitational-wave mode $(2,1)$ of non-spinning compact binaries at 3PN order, confirming previous results for the octupole and addressing UV divergences via dimensional regularization.

Contribution

It provides the first calculation of the current-type quadrupole moment and the $(2,1)$ mode at 3PN order, including a new treatment of divergences in arbitrary dimensions.

Findings

Computed the current-type quadrupole moment at 3PN order.

Calculated the $(2,1)$ gravitational-wave mode at 3.5PN correction.

Confirmed the 3PN mass-type octupole moment.

Abstract

Up to the third post-Newtonian (3PN) order, we compute (i) the current-type quadrupole moment of (non-spinning) compact binary systems, as well as (ii) the corresponding gravitational-wave mode $(2,1)$ (constituting a 3.5PN correction in the waveform). Moreover, at this occasion, (iii) we recompute and confirm the previous calculation of the mass-type octupole moment to 3PN order. The ultra-violet (UV) divergences due to the point-like nature of the source are treated by means of dimensional regularization. This entails generalizing the definition of the irreducible mass and current multipole moments of an isolated PN source in $d$ spatial dimensions. In particular, we find that the current type moment has the symmetry of a particular mixed Young tableau and that, in addition, there appears a third type of moment which is however inexistent in 3 spatial dimensions.