13,548 research outputs found
H_0 and Odds on Cosmology
Recent observations by the Hubble Space Telescope of Cepheids in the Virgo
cluster imply a Hubble Constant \ km/sec/Mpc. We attempt to
clarify some issues of interpretation of these results for determining the
global cosmological parameters and . Using the formalism of
Bayesian model comparison, the data suggest a universe with a nonzero
cosmological constant , but vanishing curvature: .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
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