2,978 research outputs found
Galaxy Bias and its Effects on the Baryon Acoustic Oscillations Measurements
The baryon acoustic oscillation (BAO) feature in the clustering of matter in
the universe serves as a robust standard ruler and hence can be used to map the
expansion history of the universe. We use high force resolution simulations to
analyze the effects of galaxy bias on the measurements of the BAO signal. We
apply a variety of Halo Occupation Distributions (HODs) and produce biased mass
tracers to mimic different galaxy populations. We investigate whether galaxy
bias changes the non-linear shifts on the acoustic scale relative to the
underlying dark matter distribution presented by Seo et al (2009). For the less
biased HOD models (b < 3), we do not detect any shift in the acoustic scale
relative to the no-bias case, typically 0.10% \pm 0.10%. However, the most
biased HOD models (b > 3) show a shift at moderate significance (0.79% \pm
0.31% for the most extreme case). We test the one-step reconstruction technique
introduced by Eisenstein et al. (2007) in the case of realistic galaxy bias and
shot noise. The reconstruction scheme increases the correlation between the
initial and final (z = 1) density fields achieving an equivalent level of
correlation at nearly twice the wavenumber after reconstruction. Reconstruction
reduces the shifts and errors on the shifts. We find that after reconstruction
the shifts from the galaxy cases and the dark matter case are consistent with
each other and with no shift. The 1-sigma systematic errors on the distance
measurements inferred from our BAO measurements with various HODs after
reconstruction are about 0.07% - 0.15%.Comment: Accepted by ApJ. 21 pages, 10 figure
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Quantum Higgs branches of isolated N=2 superconformal field theories
We study the Higgs branches of the superconformal points of four-dimensional
N=2 super Yang-Mills (SYM) which appear due to the occurrence of mutually local
monopoles having appropriate charges. We show, for example, that the maximal
superconformal point of SU(2n) SYM has a Higgs branch of the form C^2/Z_n.
These Higgs branches are intrinsic to the superconformal field theory (SCFT) at
the superconformal point, but do not appear in the SYM theory in which it is
embedded. This is because the embedding is a UV extension of the SCFT in which
some global symmetry acting on the Higgs branch is gauged irrelevantly. Higgs
branches deduced from earlier direct studies of these isolated SCFTs using BPS
wall-crossing or 3-d mirror symmetry agree with the ones we find here using
just the Seiberg-Witten data for the SYM theories.Comment: 18 page
Comparisons of Guidelines and Recommendations on Managing Antineutrophil Cytoplasmic Antibody-Associated Vasculitis.
Antineutrophil cytoplasmic antibodies-associated vasculitis (AAV) is associated with high morbidity or mortality, especially if not promptly diagnosed and treated. Many inroads have been made in the understanding of the pathophysiology that leads to exploration of novel therapies. Randomized controlled trials over the last 2 decades have better delineated and expanded therapeutic options and set the stage for an evidence-based approach. Since 2014, 4 scientific societies have systematically reviewed the existing data and have formulated evidence-based recommendations for the management of AAV. These recommendations cover diagnosis, remission induction and maintenance treatment, and prevention of long-term complications. This review is a comparative analysis of the recently published recommendations of the European League Against Rheumatism/European Renal Association-European Dialysis and Transplant Association, the British Society of Rheumatology, the Canadian Vasculitis Research Network, and the Brazilian Society of Rheumatology, and aims to determine common ground among them and highlights the differences among the recommendations
Holography of the Dirac Fluid in Graphene with Two Currents
Recent experiments have uncovered evidence of the strongly coupled nature of graphene: the Wiedemann-Franz law is violated by up to a factor of 20 near the charge neutral point. We describe this strongly coupled plasma by a holographic model in which there are two distinct conserved U(1) currents. We find that our analytic results for the transport coefficients for the two current model have a significantly improved match to the density dependence of the experimental data than the models with only one current. The additive structure in the transport coefficients plays an important role. We also suggest the origin of the two currents.Physic
The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt
We present an overview of the first data release (DR1) and first-look science
from the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green
Bank Telescope to map all Gould Belt star-forming regions with
mag visible from the northern hemisphere in emission from NH and other key
molecular tracers. This first release includes the data for four regions in
Gould Belt clouds: B18 in Taurus, NGC 1333 in Perseus, L1688 in Ophiuchus, and
Orion A North in Orion. We compare the NH emission to dust continuum
emission from Herschel, and find that the two tracers correspond closely.
NH is present in over 60\% of lines-of-sight with mag in
three of the four DR1 regions, in agreement with expectations from previous
observations. The sole exception is B18, where NH is detected toward ~ 40\%
of lines-of-sight with mag. Moreover, we find that the NH
emission is generally extended beyond the typical 0.1 pc length scales of dense
cores. We produce maps of the gas kinematics, temperature, and NH column
densities through forward modeling of the hyperfine structure of the NH
(1,1) and (2,2) lines. We show that the NH velocity dispersion,
, and gas kinetic temperature, , vary systematically between
the regions included in this release, with an increase in both the mean value
and spread of and with increasing star formation activity.
The data presented in this paper are publicly available.Comment: 33 pages, 27 figures, accepted to ApJS. Datasets are publicly
available: https://dataverse.harvard.edu/dataverse/GAS_DR
Droplets I: Pressure-Dominated Sub-0.1 pc Coherent Structures in L1688 and B18
We present the observation and analysis of newly discovered coherent
structures in the L1688 region of Ophiuchus and the B18 region of Taurus. Using
data from the Green Bank Ammonia Survey (GAS), we identify regions of high
density and near-constant, almost-thermal, velocity dispersion. Eighteen
coherent structures are revealed, twelve in L1688 and six in B18, each of which
shows a sharp "transition to coherence" in velocity dispersion around its
periphery. The identification of these structures provides a chance to study
the coherent structures in molecular clouds statistically. The identified
coherent structures have a typical radius of 0.04 pc and a typical mass of 0.4
Msun, generally smaller than previously known coherent cores identified by
Goodman et al. (1998), Caselli et al. (2002), and Pineda et al. (2010). We call
these structures "droplets." We find that unlike previously known coherent
cores, these structures are not virially bound by self-gravity and are instead
predominantly confined by ambient pressure. The droplets have density profiles
shallower than a critical Bonnor-Ebert sphere, and they have a velocity (VLSR)
distribution consistent with the dense gas motions traced by NH3 emission.
These results point to a potential formation mechanism through pressure
compression and turbulent processes in the dense gas. We present a comparison
with a magnetohydrodynamic simulation of a star-forming region, and we
speculate on the relationship of droplets with larger, gravitationally bound
coherent cores, as well as on the role that droplets and other coherent
structures play in the star formation process.Comment: Accepted by ApJ in April, 201
Low temperature thermal conductivity in a d-wave superconductor with coexisting charge order: Effect of self-consistent disorder and vertex corrections
Given the experimental evidence of charge order in the underdoped cuprate
superconductors, we consider the effect of coexisting charge order on
low-temperature thermal transport in a d-wave superconductor. Using a
phenomenological Hamiltonian that describes a two-dimensional system in the
presence of a Q=(\pi,0) charge density wave and d-wave superconducting order,
and including the effects of weak impurity scattering, we compute the
self-energy of the quasiparticles within the self-consistent Born
approximation, and calculate the zero-temperature thermal conductivity using
linear response formalism. We find that vertex corrections within the ladder
approximation do not significantly modify the bare-bubble result that was
previously calculated. However, self-consistent treatment of the disorder does
modify the charge-order-dependence of the thermal conductivity tensor, in that
the magnitude of charge order required for the system to become effectively
gapped is renormalized, generally to a smaller value.Comment: 19 pages, 15 figure
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