Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe

TL;DR

This study uses molecular absorption lines from distant quasars to set the most stringent astrophysical limit on variations in the proton-to-electron mass ratio over half the universe's age, testing fundamental physics.

Contribution

It provides the first detailed measurement of mu variation using ammonia spectra from a quasar, achieving the strongest constraint to date.

Findings

Limit on mu variation: |dmu/mu| < 1.8x10^{-6} at 95% confidence

First detailed measurement of mu using ammonia spectra in this context

Sets a new strongest astrophysical constraint on fundamental constant variation

Abstract

The Standard Model of particle physics assumes that the so-called fundamental constants are universal and unchanging. Absorption lines arising in molecular clouds along quasar sightlines offer a precise test for variations in the proton-to-electron mass ratio, mu, over cosmological time and distance scales. The inversion transitions of ammonia are particularly sensitive to mu compared to molecular rotational transitions. Comparing the available ammonia spectra observed towards the quasar B0218+357 with new, high-quality rotational spectra, we present the first detailed measurement of mu with this technique, limiting relative deviations from the laboratory value to |dmu/mu| < 1.8x10^{-6} (95% confidence level) at approximately half the Universe's current age - the strongest astrophysical constraint to date. Higher-quality ammonia observations will reduce both the statistical and systematic uncertainties in these measurements.