A nonlinear scalar model of extreme mass ratio inspirals in effective field theory II. Scalar perturbations and a master source

TL;DR

This paper develops a simplified regularization method for scalar perturbations and self-force calculations in a model of extreme mass ratio inspirals, demonstrating consistency and introducing a master source for various physical quantities.

Contribution

It introduces a simpler regularization procedure for scalar perturbations and self-force calculations, and defines a master source for deriving multiple physical observables in EMRI models.

Findings

Regular expressions for scalar perturbations are valid through third order.

The regularization method agrees with previous second-order calculations but is simpler.

The master source enables derivation of waveform, self-force, and orbital shifts.

Abstract

The motion of a small compact object (SCO) in a background spacetime is investigated further in a class of model nonlinear scalar field theories having a perturbative structure analogous to the General Relativistic description of extreme mass ratio inspirals (EMRIs). We derive regular expressions for the scalar perturbations generated by the SCO's motion valid through third order in $\epsilon$, the size of the SCO to the background curvature length scale. Our expressions are compared to those calculated through second order in $\epsilon$ by Rosenthal in [E. Rosenthal, CQG 22, S859 (2005)] and found to agree but our procedure for regularizing the scalar perturbations is considerably simpler. Following the Detweiler-Whiting (DW) scheme, we use our regular expressions for the field and derive the regular self-force corrections through third order. We find agreement with our previous derivation based on a variational principle of an effective action for the worldline associated with the SCO thus demonstrating the internal consistency of our formalism. This also explicitly demonstrates that the DW decomposition of Green's functions is a valid and practical method of self force computation at higher orders in perturbation theory and, as we show in an appendix, at all orders in perturbation theory. Finally, we identify a master source from which all other physically relevant quantities are derivable. Knowing the master source perturbatively allows one to construct the waveform measured by an observer, the regular part of the field on the worldline, the regular part of the self force, and orbital quantities such as shifts of the innermost stable circular orbit, etc. The existence of a master source together with the regularization methods implemented in this series should be indispensable for derivations of higher-order gravitational self force corrections.