18,454 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
Reflection positive doubles
Here we introduce reflection positive doubles, a general framework for reflection positivity, covering a wide variety of systems in statistical physics and quantum field theory. These systems may be bosonic, fermionic, or parafermionic in nature. Within the framework of reflection positive doubles, we give necessary and sufficient conditions for reflection positivity. We use a reflection-invariant cone to implement our construction. Our characterization allows for a direct interpretation in terms of coupling constants, making it easy to check in concrete situations. We illustrate our methods with numerous examples
Constructive simulation and topological design of protocols
We give a topological simulation for tensor networks that we call the
two-string model. In this approach we give a new way to design protocols, and
we discover a new multipartite quantum communication protocol. We introduce the
notion of topologically-compressed transformations. Our new protocol can
implement multiple, non-local compressed transformations among multi-parties
using one multipartite resource state.Comment: 16 page
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%
Nano-scale oxygen octahedral tilting in 0.90(Bi1/2Na1/2)TiO3-0.05(Bi1/2K1/2)TiO3-0.05BaTiO3 lead-free perovskite piezoelectric ceramics
The oxygen octahedral tilted domains in
0.90(Bi1/2Na1/2)TiO3-0.5(Bi1/2K1/2)TiO3-0.5BaTiO3 lead-free perovskite
piezoelectric ceramic have been studied by transmission electron microscopy
(TEM). Selected-area electron diffraction patterns shows the 1/2ooo and 1/2ooe
reflections, indicating the presence of antiphase (a-a-a-) and in-phase
(aoaoc+) octahedral tilting, respectively. The morphology and distributions of
these tilted domains are shown in the centered dark-field images. Further, the
Bragg-filtered high-resolution TEM image reveals that the size of the in-phase
tilted domains varies from 1 to 8 nm across. The ceramic contains the mixture
of non-tilted and variants of the antiphase and in-phase tilted domains.Comment: 12 pages, 3 figure
The lepton asymmetry: the last chance for a critical-density cosmology?
We use a wide range of observations to constrain cosmological models possessing a significant asymmetry in the lepton sector, which offer perhaps the best chance of reconciling a critical-density Universe with current observations. The simplest case, with massless neutrinos, fails to fit many experimental data and does not lead to an acceptable model. If the neutrinos have mass of order one electron-volt (which is favoured by some neutrino observations), then models can be implemented which prove a good fit to microwave anisotropies and large-scale structure data. However, taking into account the latest microwave anisotropy results, especially those from Boomerang, we show that the model can no longer accommodate the observed baryon fraction in clusters. Together with the observed acceleration of the present Universe, this puts considerable pressure on such critical-density models
The effect of reionization on the COBE normalization
We point out that the effect of reionization on the microwave anisotropy
power spectrum is not necessarily negligible on the scales probed by COBE. It
can lead to an upward shift of the COBE normalization by more than the
one-sigma error quoted ignoring reionization. We provide a fitting function to
incorporate reionization into the normalization of the matter power spectrum.Comment: 3 pages LaTeX file with three figures incorporated (uses mn.sty and
epsf
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