Searching for spatial variations ofα²/μin the Milky Way

Abstract

Aims. We probe the dependence of α 2 /μ on the ambient matter density by means of spectral observations in submm-and mm-wave bands. Methods. A procedure is suggested for exploring the value of F = α 2 /μ, where μ = m e /m p is the electron-to-proton mass ratio, and α = e 2 /( 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 13 CO and the fine-structure transitions in atomic carbon [C i]. A model-dependent constraint on Δα/α can be obtained from ΔF/F using Δμ/μ independently measured from the ammonia method. Results. Currently available radio astronomical datasets provide an upper limit on |ΔV| < 110 m s −1 (1σ). When interpreted in terms of the spatial variation of F, this gives |ΔF/F| < 3.7 × 10 −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 ) × 10 −8 , recently found with the ammonia method. Considering that the ammonia method restricts the spatial variation of μ at the level of |Δμ/μ| ≤ 3 × 10 −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| < 2 × 10 −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 2 × 10 −7 at high redshift if no significant temporal dependence of α is present.

An upper limit to the variation in the fundamental constants at redshiftz= 5.2

“…For comparison, in the Milky Way the [C i]/CO pairs restrict ΔF/F at the level of |ΔF/F| < 0.4 ppm (Levshakov et al 2010a) leading to a limit on |Δα/α| < 0.2 ppm since the spatial variations in μ are restricted to |Δμ/μ| < 0.03 ppm in the disk of the Milky Way (Levshakov et al 2010b;Levshakov et al 2010c;Levshakov et al 2011;Ellingsen et al 2011).…”

“…The observed correlation between the spatial distributions of C 0 and CO can be explained by clumpy PDR models (e.g., Meixner & Tielens 1995;Spaans & van Dishoeck 1997;Papadopoulos et al 2004). In the observed z = 5.2 galaxy, the derived excitation temperature of the higher-J CO lines, T ex = 40 K, and the gas density n H 2 = 3.5 × 10 3 cm −3 (CRR) just corresponds to the critical density of n cr ≈ 3 × 10 3 cm −3 required to excite collisionally the J = 2 level of the ground state triplet of C 0 (e.g., Levshakov et al 2010a). Thus, we can assume that in the present case the distributions of CO and C 0 closely trace each other.…”

Searching for chameleon-like scalar fields with the ammonia method

“…This may be the consequence of the chameleonlike scalar field. New laboratory measurements of the rest frequencies and new observations involving other rotational transitions and other targets (e.g., Levshakov et al 2010b) are required to reach more definite conclusions. ) and the corresponding χ 2 ν values.…”

Constraints on the electron-to-proton mass ratio variation at the epoch of reionization

“…A combination of [C i]/[C ii]/CO lines, -the so-called Fine Structure Method (FSM), -has already been used in differential measurements of the fundamental physical constants in a wide redshift range -from z 0 up to z 7 (Levshakov et al 2008(Levshakov et al , 2010(Levshakov et al , 2012(Levshakov et al , 2017(Levshakov et al , 2019Curran et al 2011;Weiß et al 2012). To note is also that the FSM provides, at least, a factor of 30 more sensitive probe of the variability of physical constants than traditionally used UV and optical resonance lines of atoms and ions Kozlov et al 2008).…”