Phenomenology of the Equivalence Principle with Light Scalars

TL;DR

This paper investigates how light scalar particles, called dilatons, could violate the equivalence principle by analyzing their couplings to atomic systems and deriving experimental constraints.

Contribution

It provides a general Lagrangian with five dilaton parameters and calculates the dilaton charge for atomic systems, highlighting key combinations affecting equivalence principle tests.

Findings

Identifies two main dilaton coupling combinations: nuclear binding energy variations and electromagnetism.

Provides calculations of dilaton charges for atomic systems.

Compares experimental limits on dilaton parameters.

Abstract

Light scalar particles with couplings of sub-gravitational strength, which can generically be called 'dilatons', can produce violations of the equivalence principle. However, in order to understand experimental sensitivities one must know the coupling of these scalars to atomic systems. We report here on a study of the required couplings. We give a general Lagrangian with five independent dilaton parameters and calculate the "dilaton charge" of atomic systems for each of these. Two combinations are particularly important. One is due to the variations in the nuclear binding energy, with a sensitivity scaling with the atomic number as $A^{-1/3}$. The other is due to electromagnetism. We compare limits on the dilaton parameters from existing experiments.