5,905 research outputs found
Like vs. Like: Strategy and Improvements in Supernova Cosmology Systematics
Control of systematic uncertainties in the use of Type Ia supernovae as
standardized distance indicators can be achieved through contrasting subsets of
observationally-characterized, like supernovae. Essentially, like supernovae at
different redshifts reveal the cosmology, and differing supernovae at the same
redshift reveal systematics, including evolution not already corrected for by
the standardization. Here we examine the strategy for use of empirically
defined subsets to minimize the cosmological parameter risk, the quadratic sum
of the parameter uncertainty and systematic bias. We investigate the optimal
recognition of subsets within the sample and discuss some issues of
observational requirements on accurately measuring subset properties.
Neglecting like vs. like comparison (i.e. creating only a single Hubble
diagram) can cause cosmological constraints on dark energy to be biased by
1\sigma or degraded by a factor 1.6 for a total drift of 0.02 mag. Recognition
of subsets at the 0.016 mag level (relative differences) erases bias and
reduces the degradation to 2%.Comment: 11 pages, 6 figure
Single stage experimental evaluation of slotted rotor and stator blading. Part I - Analysis and design
Analysis and design of slotted rotor and stator blading for application to compressors in advanced airbreathing propulsion system
Quasiclassical theory for the superconducting proximity effect in Dirac materials
We derive the quasiclassical non-equilibrium Eilenberger and Usadel equations
to first order in quantities small compared to the Fermi energy, valid for
Dirac edge and surface electrons with spin-momentum locking, as relevant for
topological insulators. We discuss in detail several of the key technical
points and assumptions of the derivation, and provide a Riccati-parametrization
of the equations. Solving first the equilibrium equations for S/N and S/F
bilayers and Josephson junctions, we study the superconducting proximity effect
in Dirac materials. Similarly to related works, we find that the effect of an
exchange field depends strongly on the direction of the field. Only components
normal to the transport direction lead to attenuation of the Cooper pair
wavefunction inside the F. Fields parallel to the transport direction lead to
phase-shifts in the dependence on the superconducting phase difference for both
the charge current and density of states in an S/F/S-junction. Moreover, we
compute the differential conductance in S/N and S/F bilayers with an applied
voltage bias, and determine the dependence on the length of the N and F regions
and the exchange field.Comment: 13 pages, 5 figures. Accepted for publication in Phys. Rev.
The Intrinsic Magnetization of Antiferromagnetic Textures
Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order
parameter spatially varies. This intrinsic spin is present even at equilibrium
and can be interpreted as a twisting of the homogeneous AFM into a state with a
finite spin. Because magnetic moments couple directly to external magnetic
fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic
textures under such influence. Starting from the discrete Heisenberg model, we
derive the continuum limit of the free energy of AFMs in the exchange
approximation and explicitly rederive that the spatial variation of the
antiferromagnetic order parameter is associated with an intrinsic magnetization
density. We calculate the magnetization profile of a domain wall and discuss
how the intrinsic magnetization reacts to external forces. We show
conclusively, both analytically and numerically, that a spatially inhomogeneous
magnetic field can move and control the position of domain walls in AFMs. By
comparing our model to a commonly used alternative parametrization procedure
for the continuum fields, we show that the physical interpretations of these
fields depend critically on the choice of parametrization procedure for the
discrete-to-continuous transition. This can explain why a significant amount of
recent studies of the dynamics of AFMs, including effective models that
describe the motion of antiferromagnetic domain walls, have neglected the
intrinsic spin of the textured order parameter.Comment: 12 pages, 7 figure
Model Independent Expansion History from Supernovae: Cosmology versus Systematics
We examine the Pantheon supernovae distance data compilation in a model
independent analysis to test the validity of cosmic history reconstructions
beyond the concordance CDM cosmology. Strong deviations are allowed by
the data at in the reconstructed Hubble parameter, diagnostic,
and dark energy equation of state. We explore three interpretations: 1)
possibility of the true cosmology being far from CDM, 2) supernovae
property evolution, and 3) survey selection effects. The strong (and
theoretically problematic) deviations at vanish and good
consistency with CDM is found with a simple Malmquist-like linear
correction. The adjusted data is robust against the model independent iterative
smoothing reconstruction. However, we caution that while by eye the original
deviation from CDM is striking, tests do not show the extra
linear correction parameter is statistically significant, and a
model-independent Gaussian Process regression does not find significant
evidence for the need for correction at high-redshifts.Comment: 9 pages, 6 figures, accepted for publication in MNRA
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