Angular momentum flux in scalar-tensor theories up to 1.5 post-Newtonian order

We compute the angular momentum flux from a noncircular nonspinning binary system of compact objects in massless scalar-tensor theories up to one and a half post-Newtonian (1.5PN) order using multipole moments. The angular momentum flux in scalar-tensor theories involves both a tensorial and a scalar contribution, which can be further decomposed as instantaneous, tail, and nonlinear memory effects up to 1.5PN order. We compute the explicit expressions of tail effects using the Fourier decomposition of tensorial and scalar multipole moments, and nonlinear memory effects using the Newtonian order quasi-Keplerian representation of elliptic orbits in scalar-tensor theories. This work is important to construct the radiation-reaction force and hence the waveform templates for eccentric binaries in scalar-tensor theories of gravity.