Time delays across saddles as a test of modified gravity

TL;DR

This paper proposes using lunar laser ranging and VLBI to detect or rule out modified gravity models that predict diverging time delays near gravitational saddle points, testing gravity's infrared behavior.

Contribution

It introduces observational strategies to test modified gravity theories through time-delay measurements near gravitational saddle points within the solar system.

Findings

Lunar Laser Ranging can probe time delays within meters of the saddle.

VLBI can measure delays across the Jupiter-Sun saddle.

These experiments can confirm or exclude models with infrared divergent gravity.

Abstract

Modified gravity theories can produce strong signals in the vicinity of the saddles of the total gravitational potential. In a sub-class of these models this translates into diverging time-delays for echoes crossing the saddles. Such models arise from the possibility that gravity might be infrared divergent or confined, and if suitably designed they are very difficult to rule out. We show that Lunar Laser Ranging during an eclipse could probe the time-delay effect within meters of the saddle, thereby proving or excluding these models. Very Large Baseline Interferometry, instead, could target delays across the Jupiter-Sun saddle. Such experiments would shed light on the infrared behaviour of gravity and examine the puzzling possibility that there might be well-hidden regions of strong gravity and even singularities inside the solar system.