Dynamics of the $N$-body system in energy-momentum squared gravity: Equations of motion to the first post-Newtonian order

TL;DR

This paper derives the first post-Newtonian equations of motion for an N-body system in energy-momentum squared gravity, showing that current solar system tests cannot constrain or distinguish this theory from General Relativity.

Contribution

It introduces the N-body equations of motion in the weak-field limit of EMSG and analyzes their implications for solar system tests.

Findings

EMSG effects can influence planetary perihelion shifts.

Current solar system tests do not constrain EMSG parameters.

EMSG is consistent with classical tests at first PN order.

Abstract

In the energy-momentum squared gravity (EMSG), the matter energy-momentum tensor is not conserved due to nonminimal interaction between the usual and modified matter fields. For this reason, the $N$-body acceleration may host the EMSG effects that can be probed at the solar scale by the perihelion shift of the planets and experimental tests of the Strong Equivalence Principle (SEP). To clarify this point, in this paper, we introduce the $N$-body equations of motion in the weak-field limit of the EMSG theory. To do so, the post-Newtonian (PN) hydrodynamic equations, the viral identities, as well as the corresponding equilibrium conditions are introduced in this theory. Armed with these relations, we derive the dynamics of the $N$-body system and its PN inter-body metric. It is shown that the EMSG theory is not ruled out by the classical test, the perihelion advance of Mercury, and the test of SEP. In other words, in the first PN order, it is not possible to constrain the free parameter of this theory and even distinguish it from GR using these local tests.