Searching for chameleon-like scalar fields with the ammonia method

TL;DR

This study uses high-resolution spectral observations of molecular clouds to test for variations in the electron-to-proton mass ratio, providing constraints on chameleon-like scalar field models that predict such variations depending on local matter density.

Contribution

It applies the ammonia method to measure potential variations in mu in interstellar environments, offering the most precise local constraint on mu variation to date.

Findings

Detected a statistically significant velocity offset of 23 +/- 4_stat +/- 3_sys m/s.

Inferred a variation in mu of (2.2 +/- 0.4_stat +/- 0.3_sys) x 10^{-8}.

Established an upper bound of |dmm| <= 3 x 10^{-8} at z=0.

Abstract

(Abridged) The ammonia method, which has been proposed to explore the electron-to-proton mass ratio, mu = m_e/m_p, is applied to nearby dark clouds in the Milky Way. This ratio, which is measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter is supposed to vary in chameleon-like scalar field models, which predict strong dependence of both masses and coupling constant on the local matter density. High resolution spectral observations of molecular cores in lines of NH3 (J,K) = (1,1), HC3N J = 2-1, and N2H+ J = 1-0 were performed at three radio telescopes to measure the radial velocity offsets, DeltaV = V_rot - V_inv, between the inversion transition of NH3 (1,1) and the rotational transitions of other molecules with different sensitivities to the parameter dmm = (mu_obs - mu_lab)/mu_lab. The measured values of DeltaV exhibit a statistically significant velocity offset of 23 +/- 4_stat +/- 3_sys m/s. When interpreted in terms of the electron-to-proton mass ratio variation, this infers that dmm = (2.2 +/- 0.4_stat +/- 0.3_sys)x10^{-8}. If only a conservative upper bound is considered, then the maximum offset between ammonia and the other molecules is |DeltaV| <= 30 m/s. This gives the most accurate reference point at z = 0 for dmm: |dmm| <= 3x10^{-8}.