2010A&A...516A.113L

We probe the dependence of α²/µ on the ambient matter density by means of spectral observations in submm- and mm-wave bands. A procedure is suggested for exploring the value of F=α²/µ, where µ=m_e/m_p is the electron-to-proton mass ratio, and α=e²/((h/2π)c) is the fine-structure constant. The fundamental physical constants, which are measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter are supposed to vary in chameleon-like scalar field models, which predict that both masses and coupling constant may depend on the local matter density. The parameter ΔF/F=(F_obs-F_lab)/F_lab can be estimated from the radial velocity offset, ΔV=V_rot-V_fs, between the low-laying rotational transitions in carbon monoxide ¹³CO and the fine-structure transitions in atomic carbon [CI]. A model-dependent constraint on Δα/α can be obtained from ΔF/F using Δµ/µ independently measured from the ammonia method. Currently available radio astronomical datasets provide an upper limit on |ΔV|<110m/s (1σ). When interpreted in terms of the spatial variation of F, this gives |ΔF/F|<3.7x10^–7. An order of magnitude improvement in this limit will allow us to independently test a non-zero value of Δµ/µ=(2.2±0.4_stat±0.3_sys)x10^–8, recently found with the ammonia method. Considering that the ammonia method restricts the spatial variation of µ at the level of |Δµ/µ|≤3x10^–8 and assuming that ΔF/F is the same in the entire interstellar medium, one obtains that the spatial variation of α does not exceed the value |Δα/α|< 2x10^–7. Since extragalactic gas clouds have similar densities to those in the interstellar medium, the bound on Δα/α is also expected to be less than 2x10^–7 at high redshift if no significant temporal dependence of α is present.