Satellite Test of the Equivalence Principle as a Probe of Modified Newtonian Dynamics

TL;DR

The paper proposes using the Satellite Test of the Equivalence Principle (STEP) to detect violations of the Weak Equivalence Principle and to test Modified Newtonian Dynamics (MOND) predictions in low-acceleration regimes with high precision.

Contribution

It introduces a novel application of the STEP experiment to test MOND theories by measuring oscillation frequency and amplitude changes in test masses.

Findings

MOND predicts detectable increases in oscillation frequency if the Strong Equivalence Principle holds.

MOND predicts a cumulative increase in oscillation amplitude if the Strong Equivalence Principle does not hold.

STEP can decisively test Newton's law of inertia and the equivalence principle in low-acceleration regimes.

Abstract

The proposed Satellite Test of the Equivalence Principle (STEP) will detect possible violations of the Weak Equivalence Principle by measuring relative accelerations between test masses of different composition with a precision of one part in $10^{18}$. A serendipitous byproduct of the experimental design is that the absolute (common-mode) acceleration of the test masses is also measured to high precision as they oscillate along a common axis under the influence of restoring forces produced by the position sensor currents, which in drag-free mode lead to Newtonian accelerations as small as $10^{-14}$ g. This is deep inside the low-acceleration regime where Modified Newtonian Dynamics (MOND) diverges strongly from the Newtonian limit of General Relativity. We show that MOND theories (including those based on the widely-used $n$-family of interpolating functions as well as the covariant Tensor-Vector-Scalar formulation) predict an easily detectable increase in the frequency of oscillations of the STEP test masses if the Strong Equivalence Principle holds. If it does not hold, MOND predicts a cumulative increase in oscillation amplitude which is also detectable. STEP thus provides a new and potentially decisive test of Newton's law of inertia, as well as the equivalence principle in both its strong and weak forms.