4,274 research outputs found
Non-Gaussian Halo Bias Re-examined: Mass-dependent Amplitude from the Peak-Background Split and Thresholding
Recent results of N-body simulations have shown that current theoretical
models are not able to correctly predict the amplitude of the scale-dependent
halo bias induced by primordial non-Gaussianity, for models going beyond the
simplest, local quadratic case. Motivated by these discrepancies, we carefully
examine three theoretical approaches based on (1) the statistics of thresholded
regions, (2) a peak-background split method based on separation of scales, and
(3) a peak-background split method using the conditional mass function. We
first demonstrate that the statistics of thresholded regions, which is shown to
be equivalent at leading order to a local bias expansion, cannot explain the
mass-dependent deviation between theory and N-body simulations. In the two
formulations of the peak-background split on the other hand, we identify an
important, but previously overlooked, correction to the non-Gaussian bias that
strongly depends on halo mass. This new term is in general significant for any
primordial non-Gaussianity going beyond the simplest local fNL model. In a
separate paper, we compare these new theoretical predictions with N-body
simulations, showing good agreement for all simulated types of non-Gaussianity.Comment: 26 pages, 3 figures (v2): minor changes from (v1). matches published
versio
The Larmor clock and anomalous spin dephasing in silicon
Drift-diffusion theory - which fully describes charge transport in
semiconductors - is also universally used to model transport of spin-polarized
electrons in the presence of longitudinal electric fields. By transforming spin
transit time into spin orientation with precession (a technique called the
"Larmor clock") in current-sensing vertical-transport intrinsic Si devices, we
show that spin diffusion (and concomitant spin dephasing) can be greatly
enhanced with respect to charge diffusion, in direct contrast to predictions of
spin Coulomb-drag diffusion suppression.Comment: minor edits and updated ref
Econometric analysis of volatile art markets
A new heteroskedastic hedonic regression model is suggested which takes into account time-varying volatility and is applied to a blue chips art market. A nonparametric local likelihood estimator is proposed, and this is more precise than the often used dummy variables method. The empirical analysis reveals that errors are considerably non-Gaussian, and that a student distribution with time-varying scale and degrees of freedom does well in explaining deviations of prices from their expectation. The art price index is a smooth function of time and has a variability that is comparable to the volatility of stock indices.Volatility, art markets, hedonic regression, semiparametric estimation
The profile of an emission line from relativistic outflows around a black hole
Recent observations show strong evidence for the presence of Doppler-shifted
emission lines in the spectrum of both black hole candidates and active
galactic nuclei. These lines are likely to originate from relativistic outflows
(or jets) in the vicinity of the central black hole. Consequently, the profile
of such a line should be distorted by strong gravitational effects near the
black hole, as well as special relativistic effects. In this paper, we present
results from a detailed study on how each process affects the observed line
profile. We found that the profile is sensitive to the intrinsic properties of
the jets (Lorentz factor, velocity profile, and emissivity law), as well as to
the spin of the black hole and the viewing angle (with respect to the axis of
the jets). More specifically, in the case of approaching jets, an intrisically
narrow line (blue-shifted) is seen as simply broadened at small viewing angles,
but it shows a doubly peaked profile at large viewing angles for extreme Kerr
black holes (due to the combination of gravitational focusing and Doppler
effects); the profile is always singly peaked for Schwarzschild black holes.
For receding jets, however, the line profile becomes quite complicated owing to
complicated photon trajectories. To facilitate comparison with observations, we
searched a large parameter space to derive representative line profiles. We
show the results and discuss how to use emission lines as a potential tool for
probing the inner region of a black hole jet system.Comment: 16 pages in emulateapj style, 11 figure
Control of spin coherence in semiconductor double quantum dots
We propose a scheme to manipulate the spin coherence in vertically coupled
GaAs double quantum dots. Up to {\em ten} orders of magnitude variation of the
spin relaxation and {\em two} orders of magnitude variation of the spin
dephasing can be achieved by a small gate voltage applied vertically on the
double dot. Specially, large variation of spin relaxation still exists at 0 K.
In the calculation, the equation-of-motion approach is applied to obtain the
electron decoherence time and all the relevant spin decoherence mechanisms,
such as the spin-orbit coupling together with the electron--bulk-phonon
scattering, the direct spin-phonon coupling due to the phonon-induced strain,
the hyperfine interaction and the second-order process of electron-phonon
scattering combined with the hyperfine interaction, are included. The condition
to obtain the large variations of spin coherence is also addressed.Comment: 6 pages, 4 figures, to be published in PR
Tracing Ghost Cavities with Low Frequency Radio Observations
We present X-ray and multi-frequency radio observations of the central radio
sources in several X-ray cavity systems. We show that targeted radio
observations are key to determining if the lobes are being actively fed by the
central AGN. Low frequency observations provide a unique way to study both the
lifecycle of the central radio source as well as its energy input into the ICM
over several outburst episodes.Comment: 6 pages, 4 figures, To appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", eds. H. Boehringer, P.
Schuecker, G. W. Pratt & A. Finoguenov (ESO Astrophysics Symposia,
Springer-Verlag), Garching (Germany), August 200
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