Constraints on changes in the proton–electron mass ratio using methanol lines

Abstract

We report Karl G. Jansky Very Large Array (VLA) absorption spectroscopy in four methanol (CH 3 OH) lines in the z = 0.88582 gravitational lens towards PKS1830−211. Three of the four lines have very different sensitivity coefficients K µ to changes in the proton-electron mass ratio µ; a comparison between the line redshifts thus allows us to test for temporal evolution in µ. We obtain a stringent statistical constraint on changes in µ by comparing the redshifted 12.179 GHz and 60.531 GHz lines, [∆µ/µ] 1.1 × 10 −7 (2σ) over 0 < z 0.88582, a factor of ≈ 2.5 more sensitive than the best earlier results. However, the higher signal-to-noise ratio (by a factor of ≈ 2) of the VLA spectrum in the 12.179 GHz transition also indicates that this line has a different shape from that of the other three CH 3 OH lines (at > 4σ significance). The sensitivity of the above result, and that of all earlier CH 3 OH studies, is thus likely to be limited by unknown systematic errors, probably arising due to the frequency-dependent structure of PKS1830−211. A robust result is obtained by combining the three lines at similar frequencies, 48.372, 48.377 and 60.531 GHz, whose line profiles are found to be in good agreement. This yields the 2σ constraint [∆µ/µ] 4 × 10 −7 , the most stringent current constraint on changes in µ. We thus find no evidence for changes in the proton-electron mass ratio over a lookback time of ≈ 7.5 Gyrs.

Detection of extragalactic CF+toward PKS 1830−211

“…On the other hand, CH 3 OH, HNCO, HC 3 N, and CH 3 NH 2 were found with blueshifted centroids (∼−5 km s −1 ), such as CH 3 OH here. A similar centroid was found by Kanekar et al (2015) on the line profile of several CH 3 OH lines observed at good signal-to-noise ratio with the Jansky Very Large Array. The time variations of the absorption (Muller & Guélin 2008;Muller et al 2014a) hamper the comparison of line profiles across time, but at a given epoch, the relative offsets of the line velocity centroids between different species are meaningful.…”

Fundamental constant observational bounds on the variability of the QCD scale

“…The methanol (Jansen et al 2011;Levshakov, Kozlov & Reimers 2011) and ammonia (Flambaum & Kozlov 2007) molecules are very sensitive to μ variations. Observations of methanol lines in PKS1830−211 at a redshift of 0.88582 by Bagdonaite et al (2013) and Kanekar et al (2015) have restricted μ/μ to ( − 2.9 ± 5.7) × 10 −8 , where the error is the combined statistical and systematic 1σ error. Concerns about common lines of sight have increased the error to ±1.0 × 10 −7 which is the constraint on the variation of μ used in this work.…”

The Relation between Fundamental Constants and Particle Physics Parameters

“…The radio observations, however, are significantly more accurate than the optical H 2 observations. The radio observations of methanol in PKS1830-211 [12] ( ∆µ µ = (−2.9 ± 10) × 10 −8 ) at a redshift of 0.88582 is currently the tightest constraint on a variation of µ. In spite of the relatively low redshift, the look back time is greater than half the age of the universe.…”

“…These constraints come from using (13) in (12). The ± in the ∆α α and ∆µ µ terms in Equations (14) and (15) simply reflect that limits on dα α and dµ µ are plus or minus the quoted error.…”