Equatorial periodic orbits and gravitational wave phenomenology around spherically-symmetric vacuum solution in Freund–Nambu scalar–tensor gravity
Year: 2026
Type: article
Abstract: We investigate test particle dynamics and gravitational wave (GW) phenomenology in an exact spherically symmetric vacuum solution of Freund–Nambu scalar–tensor gravity. This framework generalizes the Janis–Newman–Winicour (JNW) naked singularity via a geometric non-linear coupling q and a direct scalar-particle coupling $$g_s$$ g s . We demonstrate that these parameters systematically modify the Innermost Stable Circular Orbit (ISCO) – which shifts inward for $$g_s > 0$$ g s > 0 – and the Marginally Bound Orbit (MBO). Furthermore, we classify bound periodic trajectories to isolate extreme zoom–whirl orbits exhibiting intense periapsis precession. By applying the Numerical Kludge method to Extreme Mass-Ratio Inspirals (EMRIs), we reveal that scalar–tensor corrections induce a macroscopic temporal dephasing in high-frequency GW bursts, even when the orbit’s spatial topology is preserved. These unique phase shifts offer a robust diagnostic signature for future space-based observatories like LISA to probe the strong-field regime and constrain scalar–tensor extensions of general relativity.
Source: The European Physical Journal C
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7165687760