Equivalence principle in chameleon models

DR SUSANA LANDAU; DR. HÉCTOR VUCETICH; DR. MARCELO SALGADO; DR. MARCELO SALGADO; DR. LUCILA KRAISELBURD; DR. DANIEL SUDARSKY; DR. LUCILA KRAISELBURD; DR. DANIEL SUDARSKY; DR SUSANA LANDAU; DR. HÉCTOR VUCETICH

PHYSICAL REVIEW D

AMER PHYSICAL SOC

Lugar: New York; Año: 2018 p. 104044 - 104044

2470-0010

Most theories that predict time and/or space variation of fundamental constants also predict violations of the Weak Equivalence Principle (WEP). In 2004 Khoury and Weltman [1] proposedthe so called chameleon field arguing that it could help avoiding experimental bounds on the WEP while having a non-trivial cosmological impact. In this paper we revisit the extent to which these expectations continue to hold as we enter the regime of high precision tests. The basis of the study is the development of a new method for computing the force between two massive bodies induced by the chameleon field which takes into account the influence on the field by both, the large and thetest bodies. We confirm that in the thin shell regime the force does depend non-trivially on the test body?s composition, even when the chameleon coupling constants eta_i =eta are universal. We alsopropose a simple criterion based on energy minimization, that we use to determine which of the approximations used in computing the scalar field in a two body problem is better in each specificregime. As an application of our analysis we then compare the resulting differential acceleration of two test bodies with the corresponding bounds obtained from Eötvös type experiments. We considertwo setups: 1) an Earth based experiment where the test bodies are made of Be and Al; 2) the Lunar Laser Ranging experiment. We find that for some choices of the free parameters of the chameleonmodel the predictions of the Eötvös parameter are larger than some of the previous estimates. As a consequence, we put new constrains on these free parameters. Our conclusions strongly suggest thatthe properties of immunity from experimental tests of the WEP, usually attributed to the chameleon and related models, should be carefully reconsidered. An important result of our analysis is that our approach leads to new constraints on the parameter space of the chameleon models.