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

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.

Science, 20th June 2008. 22 pages, 5 figures (12 EPS files), 2 tables, including Supporting Online Material; v2: Corrected reference for laboratory mu-variation bounds

References in corpus (5)

• Enhanced sensitivity to time-variation of m_p/m_e in the inversion spectrum of ammonia
• Revision of VLT/UVES constraints on a varying fine-structure constant
• Comment on "Limits on the Time Variation of the Electromagnetic Fine-Structure Constant in the Low Energy Limit from Absorption Lines in the Spectra of Distant Quasars"
• Probing variations in fundamental constants with radio and optical quasar absorption-line observations
• Global 8.4-GHz VLBI observations of JVAS B0218+357

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• Sensitivity coefficients to $\alpha$-variation for fine-structure transitions in Carbon-like ions