A search for varying fundamental constants using Hz-level frequency measurements of cold CH molecules

TL;DR

This study develops a high-precision spectroscopic method to compare microwave transition frequencies in cold CH molecules from Earth and space, testing for possible variations in fundamental constants across different environments.

Contribution

It introduces a novel pulsed-beam spectroscopy technique for cold molecules and applies it to set the strongest limits yet on variations of fundamental constants between terrestrial and interstellar conditions.

Findings

No significant variation in the fine structure constant ;   1.1  10^{-7}

No significant variation in the electron-to-proton mass ratio ;   2.2  10^{-7}

Method can be used for future astrophysical constraints

Abstract

Many modern theories predict that the fundamental constants depend on time, position, or the local density of matter. We develop a spectroscopic method for pulsed beams of cold molecules, and use it to measure the frequencies of microwave transitions in CH with accuracy down to 3 Hz. By comparing these frequencies with those measured from sources of CH in the Milky Way, we test the hypothesis that fundamental constants may differ between the high and low density environments of the Earth and the interstellar medium. For the fine structure constant we find \Delta\alpha/\alpha = (0.3 +/- 1.1)*10^{-7}, the strongest limit to date on such a variation of \alpha. For the electron-to-proton mass ratio we find \Delta\mu/\mu = (-0.7 +/- 2.2) * 10^{-7}. We suggest how dedicated astrophysical measurements can improve these constraints further and can also constrain temporal variation of the constants.