Ammonia as a Tracer of Fundamental Constants

TL;DR

This paper discusses how ammonia spectral lines can be used to test for variations in fundamental constants over cosmic time, with current limits and potential for future improvements.

Contribution

It introduces ammonia as a sensitive tracer for detecting possible variations in the proton-to-electron mass ratio across cosmic history.

Findings

Current limits constrain variation to one part per million over 7 billion years.

Nearby dark clouds may show variations of 20-30 parts per billion.

Future observations could significantly improve these constraints.

Abstract

Observing inversion lines of ammonia (NH3), complemented by rotational lines of NH3 and other molecular species, provides stringent constraints on potential variations of the proton-to-electron mass ratio. While a limit of one part per million is derived for a lookback time of 7 billion years, nearby dark clouds might show a statistically significant variation of order 20-30 parts per billion, possibly being related to chameleon fields. The detection of radio-loud quasars with strong molecular absorption lines at redshifts z > 1 as well as the identification of a larger sample of nearby dark clouds with exceptionally narrow lines (<0.2 km/s) would be essential to improve present limits and to put the acquired results onto a firmer statistical basis.