Constraining the variation of fundamental constants at z ~ 1.3 using 21-cm absorbers

We present high resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) and 21-cm absorption spectra obtained with the Giant Metrewave Radio Telescope (GMRT) and the Green Bank Telescope (GBT) of five quasars along the line of sight of which 21-cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsec scale radio images of these quasars obtained with the Very Large Baseline Array (VLBA). We use the data on four of these systems to constrain the time variation of x = g_p*alpha^2/mu where g_p is the proton gyromagnetic factor, alpha is the fine structure constant, and mu is the proton-to-electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross-correlation analysis and repeated Voigt profile fitting. In two cases we also confirm our results by analysing optical spectra obtained with the Keck telescope. We find the weighted and the simple means of Delta_x / x to be respectively -(0.1 +/- 1.3)x10^-6 and (0.0 +/- 1.5)x10^-6 at the mean redshift of = 1.36 corresponding to a look back time of ~ 9 Gyr. This is the most stringent constraint ever obtained on Delta_x / x. If we only use the two systems towards quasars unresolved at milliarcsec scales, we get the simple mean of Delta_x / x = + (0.2 +/- 1.6)x10^-6. Assuming constancy of other constants we get Delta_alpha / alpha = (0.0 +/- 0.8)x10^-6 which is a factor of two better than the best constraints obtained so far using the Many Multiplet Method. On the other hand assuming alpha and g_p have not varied we derive Delta_mmu / mu = (0.0 +/- 1.5)x10^-6 which is again the best limit ever obtained on the variation of mu over this redshift range. [Abridged]Comment: 22 pages, 15 figures, Accepted for publication in MNRA

Phase transition in the fine structure constant

Within the context of mass-varying neutrinos, we construct a cosmological model that has a phase transition in the electromagnetic fine structure constant \alpha at a redshift of 0.5. The model accommodates hints of a time variable \alpha in quasar spectra and the nonobservance of such an effect at very low redshifts. It is consistent with limits from the recombination and primordial nucleosynthesis eras and is free of instabilities.Comment: 6 pages, 1 figure. Version to appear in PL

Limits on Cosmological Variation of Strong Interaction and Quark Masses from Big Bang Nucleosynthesis, Cosmic, Laboratory and Oklo Data

Recent data on cosmological variation of the electromagnetic fine structure constant from distant quasar (QSO) absorption spectra have inspired a more general discussion of possible variation of other constants. We discuss variation of strong scale and quark masses. We derive the limits on their relative change from (i) primordial Big-Bang Nucleosynthesis (BBN); (ii) Oklo natural nuclear reactor, (iii) quasar absorption spectra, and (iv) laboratory measurements of hyperfine intervals.Comment: 10 pages 2 figurs: second version have several references added and some new comment

Time variation of the fine structure constant in the early universe and the Bekenstein model

We calculate bounds on the variation of the fine structure constant at the time of primordial nucleosynthesis and at the time of neutral hydrogen formation. We use these bounds and other bounds from the late universe to test Bekenstein model. We modify the Kawano code, CAMB and CosmoMC in order to include the possible variation of the fine structure constant. We use observational primordial abundances of \De, \He and \Li, recent data from the Cosmic Microwave Background and the 2dFGRS power spectrum, to obtain bounds on the variation of $\alpha$. We calculate a piecewise solution to the scalar field equation of Bekenstein model in two different regimes; i) matter and radiation, ii) matter and cosmological constant. We match both solutions with appropriate boundary conditions. We perform a statistical analysis using the bounds obtained from the early universe and other bounds from the late universe to constrain the free parameters of the model. Results are consistent with no variation of $\alpha$ in the early universe. Limits on $\alpha$ are inconsistent with the scale length of the theory $l$ being larger than Planck scale. In order to fit all observational and experimental data, the assumption $l>L_p$ implied in Bekenstein's model has to be relaxed.Comment: 13 pages, 8 figures,version accepted to be published in Astronomy and Astrophysic

Time Variation of the Fine Structure Constant Driven by Quintessence

There are indications from the study of quasar absorption spectra that the fine structure constant $\alpha$ may have been measurably smaller for redshifts $z>2.$ Analyses of other data ($^{149}$Sm fission rate for the Oklo natural reactor, variation of $^{187}$Re $\beta$-decay rate in meteorite studies, atomic clock measurements) which probe variations of $\alpha$ in the more recent past imply much smaller deviations from its present value. In this work we tie the variation of $\alpha$ to the evolution of the quintessence field proposed by Albrecht and Skordis, and show that agreement with all these data, as well as consistency with WMAP observations, can be achieved for a range of parameters. Some definite predictions follow for upcoming space missions searching for violations of the equivalence principle.Comment: Final version, to be published in Phys Rev

A Bitter Pill: The Primordial Lithium Problem Worsens

The lithium problem arises from the significant discrepancy between the primordial 7Li abundance as predicted by BBN theory and the WMAP baryon density, and the pre-Galactic lithium abundance inferred from observations of metal-poor (Population II) stars. This problem has loomed for the past decade, with a persistent discrepancy of a factor of 2--3 in 7Li/H. Recent developments have sharpened all aspects of the Li problem. Namely: (1) BBN theory predictions have sharpened due to new nuclear data, particularly the uncertainty on 3He(alpha,gamma)7Be, has reduced to 7.4%, and with a central value shift of ~ +0.04 keV barn. (2) The WMAP 5-year data now yields a cosmic baryon density with an uncertainty reduced to 2.7%. (3) Observations of metal-poor stars have tested for systematic effects, and have reaped new lithium isotopic data. With these, we now find that the BBN+WMAP predicts 7Li/H = (5.24+0.71-0.67) 10^{-10}. The Li problem remains and indeed is exacerbated; the discrepancy is now a factor 2.4--4.3 or 4.2sigma (from globular cluster stars) to 5.3sigma (from halo field stars). Possible resolutions to the lithium problem are briefly reviewed, and key nuclear, particle, and astronomical measurements highlighted.Comment: 21 pages, 4 figures. Comments welcom

Subtle gene modification in mouse ES cells: evidence for incorporation of unmodified oligonucleotides without induction of DNA damage

Gene targeting by single-stranded oligodeoxyribonucleotides (ssODNs) is a promising tool for site-specific gene modification in mouse embryonic stem cells (ESCs). We have developed an ESC line carrying a mutant EGFP reporter gene to monitor gene correction events shortly after exposure to ssODNs. We used this system to compare the appearance and fate of cells corrected by sense or anti-sense ssODNs. The slower appearance of green fluorescent cells with sense ssODNs as compared to anti-sense ssODNs is consistent with physical incorporation of the ssODN into the genome. Thus, the supremacy of anti-sense ssODNs, previously reported by others, may be an artefact of early readout of the EGFP reporter. Importantly, gene correction by unmodified ssODNs only mildly affected the viability of targeted cells and did not induce genomic DNA double-stranded breaks (DSBs). In contrast, ssODNs that were end-protected by phosphorothioate (PTO) linkages caused increased H2AX phosphorylation and impaired cell cycle progression in both corrected and non-corrected cells due to induction of genomic DSBs. Our results demonstrate that the use of unmodified rather than PTO end-protected ssODNs allows stable gene modification without compromising the genomic integrity of the cell, which is crucial for application of ssODN-mediated gene targeting in (embryonic) stem cells

Big Bang Nucleosynthesis and Particle Dark Matter

We review how our current understanding of the light element synthesis during the Big Bang Nucleosynthesis era may help shed light on the identity of particle dark matter.Comment: a mini-review for the NJP special issue on dark matte

Models of quintessence coupled to the electromagnetic field and the cosmological evolution of alpha

We study the change of the effective fine structure constant in the cosmological models of a scalar field with a non-vanishing coupling to the electromagnetic field. Combining cosmological data and terrestrial observations we place empirical constraints on the size of the possible coupling and explore a large class of models that exhibit tracking behavior. The change of the fine structure constant implied by the quasar absorption spectra together with the requirement of tracking behavior impose a lower bound of the size of this coupling. Furthermore, the transition to the quintessence regime implies a narrow window for this coupling around $10^{-5}$ in units of the inverse Planck mass. We also propose a non-minimal coupling between electromagnetism and quintessence which has the effect of leading only to changes of alpha determined from atomic physics phenomena, but leaving no observable consequences through nuclear physics effects. In doing so we are able to reconcile the claimed cosmological evidence for a changing fine structure constant with the tight constraints emerging from the Oklo natural nuclear reactor.Comment: 13 pages, 10 figures, RevTex, new references adde

Scenario of Accelerating Universe from the Phenomenological \Lambda- Models

Dark matter, the major component of the matter content of the Universe, played a significant role at early stages during structure formation. But at present the Universe is dark energy dominated as well as accelerating. Here, the presence of dark energy has been established by including a time-dependent $\Lambda$ term in the Einstein's field equations. This model is compatible with the idea of an accelerating Universe so far as the value of the deceleration parameter is concerned. Possibility of a change in sign of the deceleration parameter is also discussed. The impact of considering the speed of light as variable in the field equations has also been investigated by using a well known time-dependent $\Lambda$ model.Comment: Latex, 9 pages, Major change