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

Abstract

Far infrared fine-structure transitions of [C i] and [C ii] and rotational transitions of CO are used to probe hypothetical variations of the electron-to-proton mass ratio µ = m e /m p at the epoch of reionization (z > 6). A constraint on ∆µ/µ = (µ obs − µ lab )/µ lab = (0.7 ± 1.2) × 10 −5 (1σ) obtained at z = 6.31 is the most stringent upto-date limit on the variation of µ at such high redshift. For all available estimates of ∆µ/µ ranging between z = 0 and z ∼ 1100, -the epoch of recombination, -a regression curve ∆µ/µ = k µ (1 + z) p , with k µ = (1.6 ± 0.3) × 10 −8 and p = 2.00 ± 0.03, is deduced. If confirmed, this would imply a dynamical nature of dark matter/dark energy.

Axi-Higgs Cosmology

“…The typical sensitivity of the QS measurements on δv is of order ∼ O(10 −5 ) − O(10 −6 ) 10 . It is limited by several factors such as Doppler noise and the background emissions [33]. Although the amplitude of δv is expected to be higher at higher z, the precisions for the QS measurements become relatively low in this case.…”

“…The lower limit of m a is set by the AC measurement of the µ drift rate [22]. The projected lower limits from astronomical observations of molecular absorption spectra, based on the present and the two-order improved precisions for eighteen known QSs [33], are also presented. The shaded purple region represents a recast of the CMB+BAO data interpretation in ΛCDM+m e (previously proposed to address the Hubble tension in [19]) in this axi-Higgs model.…”

“…The AC measurements are sensitive to the temporal drift rate of δv(t) since atomic frequen- Left: Maximal drift rate |d(δv)/dt| t 0 as a function of m a , versus the p values after marginalizing the axion oscillation phase, with the AC data [22]. Right: Maximal δv as a function of z, versus the QS data at different redshifts [33]. In both panels, we take 1.1% as the δv ini benchmark value.…”

“…The axion mass is bounded from above by requiring the axion not to roll down until near or after the recombination, and limited from below by the AC measurements on m e /m p drift rate [22] (solid-green). The projected lower limits from astronomical observations of molecular absorption spectra, in terms of the present and the two-order improved precisions for eighteen known quasars [33], are also presented (dashed-green). The CMB+BAO data, previously encoded in the ΛCDM+m e context to address the Hubble tension [19], is recast in this axi-Higgs model (with C = 0.01).…”

“…Note that the evolution of δv is described by the physics of a damped oscillator. The oscillating feature of δv may be detected by the AC measurements [20][21][22], while its non-zero value may be detected by the quasar (QS) spectral measurements [33]. With further improvements in their precisions in the near future, the axi-Higgs model should be seriously tested.…”