2,285 research outputs found
Comment on: Weak Anisotropy and Disorder Dependence of the In-Plane Magnetoresistance in High-Mobility (100) Si Inversion Layers
Comment on: Weak Anisotropy and Disorder Dependence of the In-Plane
Magnetoresistance in High-Mobility (100) Si Inversion LayersComment: 1 page, submitted to PR
Hybrid bounds for twisted L-functions
The aim of this paper is to derive bounds on the critical line Rs 1/2 for L- functions attached to twists f circle times chi of a primitive cusp form f of level N and a primitive character modulo q that break convexity simultaneously in the s and q aspects. If f has trivial nebentypus, it is shown that
L(f circle times chi, s) << (N vertical bar s vertical bar q)(epsilon) N-4/5(vertical bar s vertical bar q)(1/2-1/40),
where the implied constant depends only on epsilon > 0 and the archimedean parameter of f. To this end, two independent methods are employed to show
L(f circle times chi, s) << (N vertical bar s vertical bar q)(epsilon) N-1/2 vertical bar S vertical bar(1/2)q(3/8) and
L(g,s) << D-2/3 vertical bar S vertical bar(5/12)
for any primitive cusp form g of level D and arbitrary nebentypus (not necessarily a twist f circle times chi of level D vertical bar Nq(2))
Measuring Feedback Using the Intergalactic Medium State and Evolution Inferred from the Soft X-ray Background
We explore the intergalactic medium (IGM) as a potential source of the
unresolved soft X-ray background (XRB) and the feasibility to extract the IGM
state and evolution from XRB observations. We build two analytical models, the
continuum field model and the halo model, to calculate the IGM XRB mean flux,
angular auto correlation and cross correlation with galaxies. Our results
suggest that the IGM may contribute a significant fraction to the unresolved
soft XRB flux and correlations. We calibrated non-Gaussian errors estimated
against our moving mesh hydro simulation and estimate that the ROSAT
all sky survey plus Sloan galaxy photometric redshift survey would allow a
accuracy in the IGM XRB-galaxy cross correlation power spectrum
measurement for and a accuracy in the redshift resolved
X-ray emissivity-galaxy cross correlation power spectrum measurement for
. At small scales, non-gravitational heating, e.g. feedback,
dominates over gravity and leaves unique signatures in the IGM XRB, which
allows a comparable accuracy in the measurement of the amount of
non-gravitational heating and the length scales where non-gravitational energy
balances gravity.Comment: 17 pages, 5 figures. Will appear on ApJ May issu
Mapping dark matter with cosmic magnification
We develop a new tool to generate statistically precise dark matter maps from
the cosmic magnification of galaxies with distance estimates. We show how to
overcome the intrinsic clustering problem using the slope of the luminosity
function, because magnificability changes strongly over the luminosity
function, while intrinsic clustering only changes weakly. This may allow
precision cosmology beyond most current systematic limitations. SKA is able to
reconstruct projected matter density map at smoothing scale with
S/N, at the rate of 200-4000 deg per year, depending on the
abundance and evolution of 21cm emitting galaxies. This power of mapping dark
matter is comparable to, or even better than that of cosmic shear from deep
optical surveys or 21cm surveys.Comment: 4 pages, 1 figures. Discussions added. PRL accepte
High Resolution VLBI Astrometry of pulsar scintillation screens with the Transform
The recent development of \theta\mhyphen\theta techniques in pulsar
scintillometry has opened the door for new high resolution imaging techniques
of the scattering medium. By solving the phase retrieval problem and recovering
the wavefield from a pulsar dynamic spectrum, the Doppler shift, time delay,
and phase offset of individual images can be determined. However, the results
of phase retrieval from a single dish are only known up to a constant phase
rotation, which introduces extra parameters when doing astrometry using Very
Long Baseline Interferometry. We present an extension to previous
\theta\mhyphen\theta methods using the interferometric visibilities between
multiple stations to calibrate the wavefields. When applied to existing data
for PSR B0834+06 we measure the effective screen distance and lens orientation
with five times greater precision than previous works
Resolving the Emission Regions of the Crab Pulsar's Giant Pulses II. Evidence for Relativistic Motion
The Crab Pulsar is the prime example of an emitter of giant pulses. These
short, very bright pulses are thought to originate near the light cylinder, at
from the pulsar. The pulsar's location inside the Crab
Nebula offers an unusual opportunity to resolve the emission regions, using the
nebula, which scatters radio waves, as a lens. We attempt to do this using a
sample of 61998 giant pulses found in coherently combined European VLBI network
observations at . These were taken at times of relatively strong
scattering and hence good effective resolution, and from correlations between
pulse spectra, we show that the giant pulse emission regions are indeed
resolved. We infer apparent diameters of and
for the main and interpulse components, respectively, and show that with these
sizes the correlation amplitudes and decorrelation timescales and bandwidths
can be understood quantitatively, both in our observations and in previous
ones. Using pulse-spectra statistics and correlations between polarizations, we
also show that the nebula resolves the nanoshots that comprise individual giant
pulses. The implied diameters of far exceed light
travel-time estimates, suggesting the emitting plasma is moving
relativistically, with , as inferred previously from
drifting bands during the scattering tail of a giant pulse. If so, the emission
happens over a region extended along the line of sight by
. We conclude that relativistic motion likely is
important for producing giant pulses, and may be similarly for other sources of
short, bright radio emission, such as fast radio bursts.Comment: 29 pages, 18 figures, accepted for publication in Ap
Gravitational Lensing by Galaxy Groups in the Hubble Deep Field
We investigate strong lensing of galaxies in the Hubble Deep Field by
foreground groups and clusters of galaxies with masses from to
10^{15} \MSun. Over this mass range, groups with the profile of Navarro,
Frenk, & White (1995) are less efficient than singular isothermal spheres at
producing multiple images of galaxies, by factors of to
. This difference highlights the sensitivity of the lensing cross
section to the central density profile. Nonetheless, with either profile we
find that the expected number of galaxies lensed by groups in the Hubble Deep
Field is at most , consistent with the lack of clearly identified
group lens systems.Comment: 33 pages, 12 EPS figures, accepted by Ap
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