H_0 and Odds on Cosmology

Recent observations by the Hubble Space Telescope of Cepheids in the Virgo cluster imply a Hubble Constant $H_0=80\pm17$\ km/sec/Mpc. We attempt to clarify some issues of interpretation of these results for determining the global cosmological parameters $\Omega$ and $\Lambda$. Using the formalism of Bayesian model comparison, the data suggest a universe with a nonzero cosmological constant $\Lambda>0$, but vanishing curvature: $\Omega+\Lambda=1$.Comment: 8 Pages, uuencoded postscript. Submitted to ApJLett. Also available at file://ftp.cita.utoronto.ca/cita/andrew/papers/odds.p

Sparsely Sampling the Sky: A Bayesian Experimental Design Approach

The next generation of galaxy surveys will observe millions of galaxies over large volumes of the universe. These surveys are expensive both in time and cost, raising questions regarding the optimal investment of this time and money. In this work we investigate criteria for selecting amongst observing strategies for constraining the galaxy power spectrum and a set of cosmological parameters. Depending on the parameters of interest, it may be more efficient to observe a larger, but sparsely sampled, area of sky instead of a smaller contiguous area. In this work, by making use of the principles of Bayesian Experimental Design, we will investigate the advantages and disadvantages of the sparse sampling of the sky and discuss the circumstances in which a sparse survey is indeed the most efficient strategy. For the Dark Energy Survey (DES), we find that by sparsely observing the same area in a smaller amount of time, we only increase the errors on the parameters by a maximum of 0.45%. Conversely, investing the same amount of time as the original DES to observe a sparser but larger area of sky we can in fact constrain the parameters with errors reduced by 28%

Detection of Gravitational Waves from Inflation

Recent measurements of temperature fluctuations in the cosmic microwave background (CMB) indicate that the Universe is flat and that large-scale structure grew via gravitational infall from primordial adiabatic perturbations. Both of these observations seem to indicate that we are on the right track with inflation. But what is the new physics responsible for inflation? This question can be answered with observations of the polarization of the CMB. Inflation predicts robustly the existence of a stochastic background of cosmological gravitational waves with an amplitude proportional to the square of the energy scale of inflation. This gravitational-wave background induces a unique signature in the polarization of the CMB. If inflation took place at an energy scale much smaller than that of grand unification, then the signal will be too small to be detectable. However, if inflation had something to do with grand unification or Planck-scale physics, then the signal is conceivably detectable in the optimistic case by the Planck satellite, or if not, then by a dedicated post-Planck CMB polarization experiment. Realistic developments in detector technology as well as a proper scan strategy could produce such a post-Planck experiment that would improve on Planck's sensitivity to the gravitational-wave background by several orders of magnitude in a decade timescale.Comment: 13 page, 4 figures. To appear in the proceedings of DPF2000, Columbus, 9-12 August 2000 and (with slight revisions) in the proceedings of, "Gravitational Waves: A Challenge to Theoretical Astrophysics," Trieste, 5-9 June 200

Entry Dynamics of a Spinning Vehicle

Solution for angular motion analysis on spinning atmospheric entry vehicl