Stringent bounds to spatial variations of the electron-to-proton mass ratio in the Milky Way

✍ Scribed by P. Molaro; S.A. Levshakov; M.G. Kozlov

• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 252 KB
• Volume: 194
• Category: Article
• ISSN: 0920-5632
• DOI: 10.1016/j.nuclphysbps.2009.07.032

✦ Synopsis

The ammonia method, recently proposed by Flambaum and Kozlov (2007) to probe variations of the electronto-proton mass ratio, μ = me/mp, is applied for the first time to dense prestellar molecular clouds in the Milky Way, allowing to test Δμ/μ at different galactocentric distances. High quality radio-astronomical observations are used to check the presence of possible relative radial velocity offsets between the inversion transition of NH 3 (J, K) = (1, 1), and the CCS JN = 21 -10 and N2H + J = 1 -0 rotational transitions. Carefully selected sample of 21 NH3/CCS pairs observed in the Perseus molecular cloud provide the offset ΔVCCS-NH 3 = 36 ± 7stat ± 13.5sys m s -1 . A similar offset of ΔV = 40.8 ± 12.9stat m s -1 between NH3 (J, K) = (1, 1) and N2H + J = 1 -0 has been found in an isolated dense core L183 by Pagani et al. (2009).

Overall these observations provide a safe bound of a maximum offset between ammonia and the other molecules at the level of ΔV ≤ 100 m s -1 . Being interpreted in terms of Δμ/μ, this bound corresponds to Δμ/μ ≤ 1×10 -7 , which is an order of magnitude more sensitive than available extragalactic constraints. Taken at face value the measured ΔV shows positive shifts between the line centers of NH 3 and these two other molecules and suggest a real offset, which would imply a Δμ/μ ∼ 4 × 10 -8 . If Δμ/μ follows the gradient of the local gravitational potential, then the obtained results are in conflict with laboratory atomic clock experiments in the solar system by ∼ 5 orders of magnitude, thus requiring a chameleon-type scalar field model. New measurements involving other molecules and a wider range of objects along with verification of molecular rest frequencies are currently planned to confirm these first indications.