* Astronomy

Blobrana · L

RE: Fine structure constant

Blobrana · L

Title: Origin of pulsar pulse fine structure
Authors: O. M. Ulyanov, A. A. Seredkina, A. I. Shevtsova

We give a new numerical model of pulsar pulse radiation through the interstellar medium (ISM) considering the propagation effects. It explains the deficit of a scattering measure at the decameter range of frequencies that leads to the possibility of detecting the pulsar pulse fine structure. The results of numerical simulation confirm that the fine structure may be detected at low frequencies and this is qualitatively agreed with the observational data.

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Title: On the Evidence for Cosmic Variation of the Fine Structure Constant: A Bayesian Reanalysis of the Quasar Dataset
Authors: Ewan Cameron, Tony Pettitt

We review the evidence behind recent claims of spatial variation in the fine structure constant deriving from observations on ground-based telescopes of ionic absorption lines in the light from distant quasars. To this end we expand upon previous non-Bayesian analyses limited by the assumptions of a strictly Normal and unbiased form for the "unexplained errors" of the benchmark quasar dataset. Through nested importance sampling and the method of power posteriors we evaluate and compare marginal likelihoods (or Bayes factors) for three competing hypotheses-(i) the strict null (no cosmic variation), (ii) the monopole null (a constant Earth-to-quasar offset only), and (iii) the monopole+dipole hypothesis (featuring a cosmic variation manifest to the Earth-bound observer as a North-South divergence)-under various alternative error terms. Our analysis reveals significant support for a skeptical interpretation in which the apparent dipole effect is driven solely by systematic errors of opposing sign inherent in measurements from the two telescopes employed to obtain the observations. In this context we highlight the importance of new observations along the equator of the alleged dipole (in addition to the new polar observations planned) in order to more strongly test the skeptical interpretation.

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Title: Estimations of the cosmological parameters from the observational variation of the fine structure constant
Authors: Zhong-Xu Zhai, Xian-Ming Liu, Zhi-Song Zhang, Tong-Jie Zhang

We present the constraints on the Quintessence scalar field model from the observational data of the variation of the fine structure constant obtained from Keck and VLT telescopes. Within the theoretical frame proposed by Bekenstein, the constraints on the parameters of the Quintessence scalar field model are obtained. By the consideration of the prior of \Omega_{m0} as WMAP 7 suggests, we obtain various results of the different samples. Based on these results, we also calculate the probability density function of the coupling constant \zeta. The best-fit values show a consistent relationship between \zeta and the different experimental results. In our work, we test two different potential models, namely, the inverse power law potential and the exponential potential. The results show that both the large value of the parameters in the potential and the strong coupling can cause the variation of fine structure constant.

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Title: Is there correlation between Fine Structure and Dark Energy Cosmic Dipoles?
Authors: Antonio Mariano, Leandros Perivolaropoulos

We present a detailed analysis (including redshift tomography) of the cosmic dipoles in the Keck+VLT quasar absorber and in the Union2 SnIa samples. We show that the fine structure constant cosmic dipole obtained through the Keck+VLT quasar absorber sample at 4.1\sigma level, is anomalously aligned with the corresponding dark energy dipole obtained through the Union2 sample at 2\sigma level. The angular separation between the two dipole directions is 11.3° ±11.8°. We use Monte Carlo simulations to find the probability of obtaining the observed dipole magnitudes with the observed alignment, in the context of an isotropic cosmological model with no correlation between dark energy and fine structure constant. We find that this probability is less than one part in 10^6. We propose a simple physical model (extended topological quintessence) which naturally predicts spherical inhomogeneous distribution for both dark energy density and fine structure constant values. The model is based on the existence of a recently formed giant global monopole with Hubble scale core which also couples non-minimally to electromagnetism. Aligned dipole anisotropies would naturally emerge for an off-center observer for both the fine structure constant and for dark energy density. This model smoothly reduces to \lcdm for proper limits of its parameters.

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Title: Is there a spatial gradient in values of the fine-structure constant? A reanalysis of the results
Authors: J. C. Berengut, E. M. Kava, V. V. Flambaum

We statistically analyse a recent sample of data points measuring the fine-structure constant alpha (relative to the terrestrial value) in quasar absorption systems. Using different statistical techniques, we find general agreement with previous authors that a dipole model is a well-justified fit to the data. We determine the significance of the dipole fit relative to that of a simple monopole fit, discuss the consistency of the interpretation, and test alternate models for potential variation of alpha against the data. Using a simple analysis we find that the monopole term (the constant offset in (delta alpha)/alpha) may be caused by non-terrestrial magnesium isotope abundances in the absorbers. Finally we test the domain-wall model against the data.

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Blobrana · L

Title: Searching for variations in the fine-structure constant and the proton-to-electron mass ratio using quasar absorption lines
Authors: Julian A. King

Quasar absorption lines provide a precise test of the assumed constancy of the fundamental constants of physics. We have investigated potential changes in the fine-structure constant, alpha, and the proton-to-electron mass ratio, mu. The many-multiplet method allows one to use optical fine-structure transitions to constrain (Delta alpha)/alpha at better than the 10^(-5) level. We present a new analysis of 154 quasar absorbers with 0.2 < z 1.6 sub-samples independently yield consistent estimates of the dipole direction, which suggests that the effect is not caused by telescope systematics. We consider a number of systematic effects and show that they are unable to explain the observed dipole effect. We have used spectra of the quasars Q0405-443, Q0347-383 and Q0528-250 from VLT/UVES to investigate the absorbers at z=2.595, 3.025 and 2.811 in these spectra respectively. We find that (Delta mu)/mu=(10.1 ± 6.6) x 10^(-6), (8.2 ± 7.5) x 10^(-6) and (-1.4 ± 3.9) x 10^(-6) in these absorbers respectively. A second spectrum of Q0528-250 provides an additional constraint of (Delta mu)/mu=(0.2 ± 3.2_stat ± 1.9_sys) x 10^(-6). The weighted mean of these values yields (Delta mu)/mu=(1.7 ± 2.4) x 10^(-6), the most precise constraint on evolution in mu at z>1.

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Title: Spatial variation in the fine-structure constant -- new results from VLT/UVES
Authors: Julian A. King, John K. Webb, Michael T. Murphy, Victor V. Flambaum, Robert F. Carswell, Matthew B. Bainbridge, Michael R. Wilczynska, F. Elliot Koch

We present a new analysis of a large sample of quasar absorption-line spectra obtained using UVES (the Ultraviolet and Visual Echelle Spectrograph) on the VLT (Very Large Telescope) in Chile. In the VLT sample (154 absorbers), we find evidence that alpha increases with increasing cosmological distance from Earth. However, as previously shown, the Keck sample (141 absorbers) provided evidence for a smaller alpha in the distant absorption clouds. Upon combining the samples an apparent variation of alpha across the sky emerges which is well represented by an angular dipole model pointing in the direction RA=(17.3 ±1.0) hr, dec. = (-61 ±10) deg, with amplitude (0.97 +0.22/-0.20) x 10^(-5). The dipole model is required at the 4.1 sigma statistical significance level over a simple monopole model where alpha is the same across the sky (but possibly different to the current laboratory value). The data sets reveal a number of remarkable consistencies: various data cuts are consistent and there is consistency in the overlap region of the Keck and VLT samples. Assuming a dipole-only (i.e. no-monopole) model whose amplitude grows proportionally with 'lookback-time distance' (r=ct, where t is the lookback time), the amplitude is (1.1 ±0.2) x 10^(-6) GLyr^(-1) and the model is significant at the 4.2 sigma confidence level over the null model [Delta alpha]/alpha = 0). We apply robustness checks and demonstrate that the dipole effect does not originate from a small subset of the absorbers or spectra. We present an analysis of systematic effects, and are unable to identify any single systematic effect which can emulate the observed variation in alpha.

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Title: The Fine Structure Constant and the CMB Damping Scale
Authors: Eloisa Menegoni, Maria Archidiacono, Erminia Calabrese, Silvia Galli, C. J. A. P. Martins, Alessandro Melchiorri

The recent measurements of the Cosmic Microwave Background anisotropies at arcminute angular scales performed by the ACT and SPT experiments are probing the damping regime of CMB fluctuations. The analysis of these datasets unexpectedly suggests that the effective number of relativistic degrees of freedom is larger than the standard value of Neff = 3.04, and inconsistent with it at more than two standard deviations. In this paper we study the role of a mechanism that could affect the shape of the CMB angular fluctuations at those scales, namely a change in the recombination process through variations in the fine structure constant. We show that the new CMB data significantly improve the previous constraints on variations of {\alpha}, with {\alpha}/{\alpha}0 = 0.984 ± 0.005, i.e. hinting also to a more than two standard deviation from the current, local, value {\alpha}0. A significant degeneracy is present between {\alpha} and Neff, and when variations in the latter are allowed the constraints on {\alpha} are relaxed and again consistent with the standard value. Deviations of either parameter from their standard values would imply the presence of new, currently unknown physics.

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Blobrana · L

Nature's laws may vary across the Universe

One of the laws of nature may vary across the Universe, according to a study published today in the journal Physical Review Letters.
One of the most cherished principles in science - the constancy of physics - may not be true, according to research carried out at the University of New South Wales (UNSW), Swinburne University of Technology and the University of Cambridge.
The study found that one of the four known fundamental forces, electromagnetism - measured by the so-called fine-structure constant and denoted by the symbol 'alpha' - seems to vary across the Universe.
The first hints that alpha might not be constant came a decade ago when Professor John Webb, Professor Victor Flambaum, and other colleagues at UNSW and elsewhere, analysed observations from the Keck Observatory, in Hawaii. Those observations were restricted to one broad area in the sky.
However, now Webb and colleagues (PhD graduate Dr Julian King, PhD student Matthew Bainbridge and Professor Victor Flambaum at UNSW; Dr Michael Murphy at Swinburne University of Technology, and Professor Bob Carswell from Cambridge University) have doubled the number of observations and measured the value of alpha in about 300 distant galaxies, all at huge distances from Earth, and over a much wider area of the sky. The new observations were obtained using the European Southern Observatory's 'Very Large Telescope' in Chile.
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