Probing the electron-to-proton mass ratio gradient in the Milky Way with Class I methanol masers
Artikel i vetenskaplig tidskrift, 2022

We estimate limits on non-universal coupling of hypothetical hidden fields to standard matter by evaluating the fractional changes in the electron-to-proton mass ratio, mu = m(e)/m(p), based on observations of Class I methanol masers distributed in the Milky Way disc over the range of the Galactocentric distances 4 less than or similar to R less than or similar to 12 kpc. The velocity offsets Delta V = V-44 - V-95 measured between the 44- and 95-GHz methanol lines provide, so far, one of the most stringent constraints on the spatial gradient k(mu)= d(Delta mu/mu)/dR < 2 x10(-9) kpc(-1) and the upper limit on Delta mu/mu <2 x 10(-8), where Delta mu/mu = (mu(obs) - mu(lab))/mu(lab). We also find that the offsets Delta V are clustered into two groups which are separated by delta(Delta V) = 0.022 +/- 0.003 km s(-1) (1 sigma confidence level). The grouping is most probably due to the dominance of different hyperfine transitions in the 44- and 95-GHz methanol maser emission. Which transition becomes favoured is determined by an alignment (polarization) of the nuclear spins of the four hydrogen atoms in the methanol molecule. This result confirms that there are preferred hyperfine transitions involved in the methanol maser action.

elementary particles

methods: observational

ISM: molecules

techniques: spectroscopic



S. A. Levshakov

Saint Petersburg Electrotechnical University

National Research Centre "Kurchatov Institute"

Russian Academy of Sciences

I. I. Agafonova

Saint Petersburg Electrotechnical University

C. Henkel

Chinese Academy of Sciences


King Abdulaziz University

Kee-Tae Kim

University of Science and Technology (UST)

Korea Astronomy and Space Science Institute

M. G. Kozlov

Saint Petersburg Electrotechnical University

National Research Centre "Kurchatov Institute"

Boy Lankhaar

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik

W. Yang


Monthly Notices of the Royal Astronomical Society

0035-8711 (ISSN) 1365-2966 (eISSN)

Vol. 511 1 413-424


Subatomär fysik

Astronomi, astrofysik och kosmologi

Teoretisk kemi



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