Narrow Results

A modified $f(R)$ viable model is proposed that behaves asymptotically as $\mathrm{\Lambda }$CDM and satisfies cosmological and local gravity constraints. Apart from a mass scale that is a priori defined, the model contains only one additional parameter, which is determined by the current value of the matter density parameter ${\mathrm{\Omega }}_{m0}$. Under the chameleon mechanism the model satisfies the thin shell restrictions for local gravity systems without imposing additional restrictions on model parameters. Signals of scalar–tensor regime in the growth of matter perturbations, are present. Using the mass scale to determine the matter density parameter today, the remaining free parameter covers the whole range of values needed to test the model against the more stringent constraints arising at galactic and galactic cluster scales. The finite time singularity of the model was analyzed. A comparison was made with known models with the same number of parameters.

Observing inversion lines of ammonia (NH3), complemented by rotational lines of NH3 and other molecular species, provides stringent constraints on potential variations of the proton-to-electron mass ratio, μ. While a limit of |Δμ|/μ ~ 10⁻⁶ is derived for a lookback time of 7 × 10⁹ yr, nearby dark clouds might show a significant variation of order (2 − 3) × 10⁻⁸, possibly being related to chameleon fields. The detection of radioloud quasars with strong molecular absorption lines at redshifts z > 1 as well as the identification of a larger sample of nearby molecular clouds with exceptionally narrow lines (ΔV < 0.2kms⁻¹) would be essential to improve present limits and to put the acquired results onto a firmer statistical basis.