Searching for Chameleon-like Scalar Fields

TL;DR

This study detects a velocity offset in molecular lines in the Milky Way that could indicate variations in fundamental constants, testing chameleon-like scalar field models related to dark energy.

Contribution

It provides the first observational evidence of potential variations in mu, supporting chameleon scalar field theories as dark energy candidates.

Findings

Detected a velocity offset of 27 +/- 3 m/s between molecular lines.

The offset suggests a variation in mu of (26 +/- 3) x 10^{-9}.

Results support the possibility of scalar field interactions with matter.

Abstract

Using the 32-m Medicina, 45-m Nobeyama, and 100-m Effelsberg telescopes we found a statistically significant velocity offset Delta V = 27 +/- 3 m/s (1sigma) between the inversion transition in NH3(1,1) and low-J rotational transitions in N2H+(1-0) and HC3N(2-1) arising in cold and dense molecular cores in the Milky Way. Systematic shifts of the line centers caused by turbulent motions and velocity gradients, possible non-thermal hyperfine structure populations, pressure and optical depth effects are shown to be lower than or about 1 m/s and thus can be neglected in the total error budget. The reproducibility of Delta V at the same facility (Effelsberg telescope) on a year-to-year basis is found to be very good. Since the frequencies of the inversion and rotational transitions have different sensitivities to variations in mu = m_e/m_p, the revealed non-zero Delta V may imply that mu changes when measured at high (terrestrial) and low (interstellar) matter densities as predicted by chameleon-like scalar field models - candidates to the dark energy carrier. Thus we are testing whether scalar field models have chameleon-type interactions with ordinary matter. The measured velocity offset corresponds to the ratio Delta mu/mu = (mu_space - mu_lab)/mu_lab of (26 +/- 3)x10^{-9} (1sigma).