Markov Chain Monte Carlo methods applied to measuring the fine structure constant from quasar spectroscopy .
Abstract
Recent attempts to constrain cosmological variation in the fine structure constant, alpha , using quasar absorption lines have yielded two statistical samples which initially appear to be inconsistent. One of these samples was subsequently demonstrated to not pass consistency tests; it appears that the optimisation algorithm used to fit the model to the spectra failed. Nevertheless, the results of the other hinge on the robustness of the spectral fitting program VPFIT, which has been tested through simulation but not through direct exploration of the likelihood function. We present the application of Markov Chain Monte Carlo (MCMC) methods to this problem, and demonstrate that VPFIT produces similar values and uncertainties for Delta alpha /alpha , the fractional change in the fine structure constant, as our MCMC algorithm, and thus that VPFIT is reliable.
 Publication:

Memorie della Societa Astronomica Italiana
 Pub Date:
 2009
 arXiv:
 arXiv:0910.2699
 Bibcode:
 2009MmSAI..80..864K
 Keywords:

 Atomic processes;
 Methods: numerical;
 Methods: statistical;
 Quasars: absorption lines;
 Quasars: individual: LBQS 22061958;
 Quasars: individual: LBQS 00130029;
 Quasars: individual: Q 0551366;
 Cosmology: observations;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 IAU 2009 JD9 conference proceedings. 6 pages, 2 figures. MmSAI, vol. 80 in press Paolo Molaro &