65,249 research outputs found
Axion hot dark matter bounds
We derive cosmological limits on two-component hot dark matter consisting of
neutrinos and axions. We restrict the large-scale structure data to the safely
linear regime, excluding the Lyman-alpha forest. We derive Bayesian credible
regions in the two-parameter space consisting of m_a and sum(m_nu).
Marginalizing over sum(m_nu) provides m_a<1.02 eV (95% CL). In the absence of
axions the same data and methods give sum(m_nu)< 0.63 eV (95% CL).Comment: Contribution to Proc. 4th Patras Workshop on Axions, WIMPs and WISPs
(18-21 June 2008, DESY
Television signal processing system Patent
Video signal processing system for sampling video brightness level
Video signal enhancement system with dynamic range compression and modulation index expansion Patent
Video signal enhancement of signal component representing brightness of scene element in low contras
Improved television signal processing system
Digital system processes spacecraft television pictures by converting images sensed on a photostorage vidicon to pulses which can be transmitted by telemetry. This system can be applied in the processing of medical X ray photographs and in electron microscopy
Application of Pad\'{e} interpolation to stationary state problems
If the small and large coupling behavior of a physical system can be computed
perturbatively and expressed respectively as power series in a coupling
parameter and , a Pad\'{e} approximant embracing the two series can
interpolate between these two limits and provide an accurate estimate of the
system's behavior in the generally intractable intermediate coupling regime.
The methodology and validity of this approach are illustrated by considering
several stationary state problems in quantum mechanics.Comment: RevTeX4, 7 pages (including 7 tables); v4 typos correcte
How CMB and large-scale structure constrain chameleon interacting dark energy
We explore a chameleon type of interacting dark matter-dark energy scenario
in which a scalar field adiabatically traces the minimum of an effective
potential sourced by the dark matter density. We discuss extensively the effect
of this coupling on cosmological observables, especially the parameter
degeneracies expected to arise between the model parameters and other
cosmological parameters, and then test the model against observations of the
cosmic microwave background (CMB) anisotropies and other cosmological probes.
We find that the chameleon parameters and , which determine
respectively the slope of the scalar field potential and the dark matter-dark
energy coupling strength, can be constrained to and using CMB data alone. The latter parameter in particular is constrained
only by the late Integrated Sachs-Wolfe effect. Adding measurements of the
local Hubble expansion rate tightens the bound on by a factor of
two, although this apparent improvement is arguably an artefact of the tension
between the local measurement and the value inferred from Planck data in
the minimal CDM model. The same argument also precludes chameleon
models from mimicking a dark radiation component, despite a passing similarity
between the two scenarios in that they both delay the epoch of matter-radiation
equality. Based on the derived parameter constraints, we discuss possible
signatures of the model for ongoing and future large-scale structure surveys.Comment: 25 pages, 6 figure
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