Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
Michael T. Murphy,1*
Victor V. Flambaum,2
Sébastien Muller,3
Christian Henkel4
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, µ, over cosmological time and distance scales. The inversion transitions of ammonia are particularly sensitive to µ as compared to molecular rotational transitions. Comparing the available ammonia spectra observed toward the quasar B0218+357 with new, high-quality rotational spectra, we present the first detailed measurement of µ with this technique, limiting relative deviations from the laboratory value to |
µ/µ| < 1.8 x 10–6 (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 observations.
1 Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H39, Post Office Box 218, Victoria 3122, Australia.
2 School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia.
3 Academia Sinica Institute of Astronomy and Astrophysics, Post Office Box 23-141, Taipei, 106 Taiwan.
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
* To whom correspondence should be addressed. E-mail: mmurphy{at}swin.edu.au