Methanol isotopologues as a probe for spatial and temporal variations of the electron-to-proton mass ratio

TL;DR

This study calculates the sensitivity of methanol isotopologue microwave transitions to potential variations in the electron-to-proton mass ratio, enabling tests of fundamental physics over cosmic distances.

Contribution

It introduces new sensitivity coefficients for methanol isotopologues, expanding tools for probing fundamental constant variations in space and time.

Findings

Methanol isotopologues have a wide range of Qmu sensitivity coefficients.

Observed lines constrain mu variation to 3x10^-8 in star-forming regions.

Results align with previous limits from methanol and other molecules.

Abstract

We present results on numerical calculations of the sensitivity coefficients, Qmu, of microwave molecular transitions in (13C)H3OH and CH3(18O)H to the hypothetical variation in the fundamental physical constant mu - the electron-to-proton mass ratio. The invariability of mu in time and space is one of the basic assumptions of the Standard Model of particle physics which can be tested at cosmological scales by means of astronomical observations in the Galaxy and external galaxies. Our calculations show that these two methanol isotopologues can be utilized for such tests since their microwave transitions from the frequency interval 1-100 GHz exhibit a large spread in Qmu values which span a range of -109 < Qmu < 78. We show that the thermal emission lines of (13C)H3OH observed in the star-forming region NGC6334I constrain the variability of mu at a level of 3x10^-8 (1{\sigma}), which is in line with the most stringent upper limits obtained previously from observations of methanol (CH3OH) and other molecules in the Galaxy.