MICROSCOPE mission: first constraints on the violation of the weak equivalence principle by a light scalar dilaton

TL;DR

The MICROSCOPE experiment's initial results significantly tighten constraints on light scalar fields that could violate the weak equivalence principle, especially for fields with masses below 10^{-12} eV, by improving existing bounds by an order of magnitude.

Contribution

This study provides the first constraints on light scalar dilatons from MICROSCOPE data, enhancing previous limits on their coupling to matter and testing fundamental physics.

Findings

Constraints on scalar coupling strength improved by an order of magnitude.

Limits on dilaton parameters are tightened for masses below 10^{-12} eV.

Results exclude certain scalar field models with weaker couplings.

Abstract

The existence of a light or massive scalar field with a coupling to matter weaker than gravitational strength is a possible source of violation of the weak equivalence principle. We use the first results on the E\"otv\"os parameter by the MICROSCOPE experiment to set new constraints on such scalar fields. For a massive scalar field of mass smaller than $10^{-12}$ eV (i.e. range larger than a few $10^5$ m) we improve existing constraints by one order of magnitude to $|\alpha|<10^{-11}$ if the scalar field couples to the baryon number and to $|\alpha|<10^{-12}$ if the scalar field couples to the difference between the baryon and the lepton numbers. We also consider a model describing the coupling of a generic dilaton to the standard matter fields with five parameters, for a light field: we find that for masses smaller than $10^{-12}$eV, the constraints on the dilaton coupling parameters are improved by one order of magnitude compared to previous equivalence principle tests.