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Register a new userDoes the proton-to-electron mass ratio vary in the course of cosmological evolution?
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A.Ivanchik
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The possible cosmological variation of the proton-to-electron mass ratio was estimated by measuring the H_2 wavelengths in the high-resolution spectrum of the quasar Q~0347-382. Our analysis yielded an estimate for the possible deviation of mu value in the past, 10 Gyr ago: for the unweighted value $Delta mu / mu = (3.0pm2.4)times10^{-5}$; for the weighted value [ Delta mu / mu = (5.02pm1.82)times10^{-5}] Since the significance of the both results does not exceed 3$sigma$, further observations are needed to increase the statistical significance. In any case, this result may be considered as the most stringent estimate on an upper limit of a possible variation of mu (95% C.L.): [ |Delta mu / mu| < 8times 10^{-5} ] This value serves as an effective tool for selection of models determining a relation between possible cosmological deviations of the fine-structure constant alpha and the elementary particle masses (m$_p$, m$_e$, etc.).
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Multidimensional cosmologies allow for variations of fundamental physical constants over the course of cosmological evolution, and differe
We estimate the cosmological variation of the proton-to-electron mass ratio mu=m_p/m_e by measuring the wavelengths of molecular hydrogen transitions in the early universe. The analysis is performed using high spectral resolution observations (FWHM ~ 7 km/s) of two damped Lyman-alpha systems at z_{abs}=2.3377 and 3.0249 observed along the lines of sight to the quasars Q 1232+082 and Q 0347-382 respectively. The most conservative result of the analysis is a possible variation of mu over the last ~ 10 Gyrs, with an amplitude Deltamu/mu = (5.7+-3.8)x10^{-5}. The result is significant at the 1.5sigma level only and should be confirmed by further observations. This is the most stringent estimate of a possible cosmological variation of mu obtained up to now.
A new limit on the possible cosmological variation of the proton-to-electron mass ratio mu=m_p/m_e is estimated by measuring wavelengths of H_2 lines of Lyman and Werner bands from two absorption systems at z_abs = 2.5947 and 3.0249 in the spectra of quasars Q 0405-443 and Q 0347-383, respectively. Data are of the highest spectral resolution (R = 53000) and S/N ratio (30div70) for this kind of study. We search for any correlation between z_i, the redshift of observed lines, determined using laboratory wavelengths as references, and K_i, the sensitivity coefficient of the lines to a change of mu, that could be interpreted as a variation of mu over the corresponding cosmological time. We use two sets of laboratory wavelengths, the first one, Set (A) (Abgrall et al.), based on experimental determination of energy levels and the second one, Set (P) (Philip et al.), based on new laboratory measurements of some individual rest-wavelengths. We find Deltamu/mu = (3.05+-0.75)10^-5 for Set (A), and Deltamu/mu = (1.65+-0.74)10^-5 for Set (P). The second determination is the most stringent limit on the variation of mu over the last 12 Gyrs ever obtained. The correlation found using Set (A) seems to show that some amount of systematic error is hidden in the determination of energy levels of the H$_2$ molecule.
Molecular transitions recently discovered at redshift z_abs=2.059 toward the bright background quasar J2123-0050 are analysed to limit cosmological variation in the proton-to-electron mass ratio, mu=m_p/m_e. Observed with the Keck telescope, the optical echelle spectrum has the highest resolving power and largest number (86) of H_2 transitions in such analyses so far. Also, (seven) HD transitions are used for the first time to constrain mu-variation. These factors, and an analysis employing the fewest possible free parameters, strongly constrain mus relative deviation from the current laboratory value: dmu/mu =(+5.6+/-5.5_stat+/-2.9_sys)x10^{-6}, indicating an insignificantly larger mu in the absorber. This is the first Keck result to complement recent null constraints from three systems at z_abs>2.5 observed with the Very Large Telescope. The main possible systematic errors stem from wavelength calibration uncertainties. In particular, distortions in the wavelength solution on echelle order scales are estimated to contribute approximately half the total systematic error component, but our estimate is model dependent and may therefore under or overestimate the real effect, if present. To assist future mu-variation analyses of this kind, and other astrophysical studies of H_2 in general, we provide a compilation of the most precise laboratory wavelengths and calculated parameters important for absorption-line work with H_2 transitions redwards of the hydrogen Lyman limit.
Yes, but only for a parameter value that makes it almost coincide with the standard model. We reconsider the cosmological dynamics of a generalized Chaplygin gas (gCg) which is split into a cold dark matter (CDM) part and a dark energy (DE) component with constant equation of state. This model, which implies a specific interaction between CDM and DE, has a $Lambda$CDM limit and provides the basis for studying deviations from the latter. Including matter and radiation, we use the (modified) CLASS code cite{class} to construct the CMB and matter power spectra in order to search for a gCg-based concordance model that is in agreement with the SNIa data from the JLA sample and with recent Planck data. The results reveal that the gCg parameter $alpha$ is restricted to $|alpha|lesssim 0.05$, i.e., to values very close to the $Lambda$CDM limit $alpha =0$. This excludes, in particular, models in which DE decays linearly with the Hubble rate.
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