20,378 research outputs found
The Impact of Line Misidentification on Cosmological Constraints from Euclid and other Spectroscopic Galaxy Surveys
We perform forecasts for how baryon acoustic oscillation (BAO) scale and
redshift-space distortion (RSD) measurements from future spectroscopic emission
line galaxy (ELG) surveys such as Euclid are degraded in the presence of
spectral line misidentification. Using analytic calculations verified with mock
galaxy catalogs from log-normal simulations we find that constraints are
degraded in two ways, even when the interloper power spectrum is modeled
correctly in the likelihood. Firstly, there is a loss of signal-to-noise ratio
for the power spectrum of the target galaxies, which propagates to all
cosmological constraints and increases with contamination fraction, .
Secondly, degeneracies can open up between and cosmological parameters.
In our calculations this typically increases BAO scale uncertainties at the
10-20% level when marginalizing over parameters determining the broadband power
spectrum shape. External constraints on , or parameters determining the
shape of the power spectrum, for example from cosmic microwave background (CMB)
measurements, can remove this effect. There is a near-perfect degeneracy
between and the power spectrum amplitude for low values, where
is not well determined from the contaminated sample alone. This has the
potential to strongly degrade RSD constraints. The degeneracy can be broken
with an external constraint on , for example from cross-correlation with a
separate galaxy sample containing the misidentified line, or deeper
sub-surveys.Comment: 18 pages, 7 figures, updated to match version accepted by ApJ (extra
paragraph added at the end of Section 4.3, minor text edits
Probing Cosmic Strings with Satellite CMB measurements
We study the problem of searching for cosmic string signal patterns in the
present high resolution and high sensitivity observations of the Cosmic
Microwave Background (CMB). This article discusses a technique capable of
recognizing Kaiser-Stebbins effect signatures in total intensity anisotropy
maps, and shows that the biggest factor that produces confusion is represented
by the acoustic oscillation features of the scale comparable to the size of
horizon at recombination. Simulations show that the distribution of null
signals for pure Gaussian maps converges to a distribution, with
detectability threshold corresponding to a string induced step signal with an
amplitude of about 100 \muK which corresponds to a limit of roughly . We study the statistics of spurious detections caused by
extra-Galactic and Galactic foregrounds. For diffuse Galactic foregrounds,
which represents the dominant source of contamination, we derive sky masks
outlining the available region of the sky where the Galactic confusion is
sub-dominant, specializing our analysis to the case represented by the
frequency coverage and nominal sensitivity and resolution of the Planck
experiment.Comment: 14 pages, 3 figures, to be published in JCA
Modularity and community structure in networks
Many networks of interest in the sciences, including a variety of social and
biological networks, are found to divide naturally into communities or modules.
The problem of detecting and characterizing this community structure has
attracted considerable recent attention. One of the most sensitive detection
methods is optimization of the quality function known as "modularity" over the
possible divisions of a network, but direct application of this method using,
for instance, simulated annealing is computationally costly. Here we show that
the modularity can be reformulated in terms of the eigenvectors of a new
characteristic matrix for the network, which we call the modularity matrix, and
that this reformulation leads to a spectral algorithm for community detection
that returns results of better quality than competing methods in noticeably
shorter running times. We demonstrate the algorithm with applications to
several network data sets.Comment: 7 pages, 3 figure
Galaxy-CMB and galaxy-galaxy lensing on large scales: sensitivity to primordial non-Gaussianity
A convincing detection of primordial non-Gaussianity in the local form of the
bispectrum, whose amplitude is given by the fNL parameter, offers a powerful
test of inflation. In this paper we calculate the modification of two-point
cross-correlation statistics of weak lensing - galaxy-galaxy lensing and
galaxy-Cosmic Microwave Background (CMB) cross-correlation - due to fNL. We
derive and calculate the covariance matrix of galaxy-galaxy lensing including
cosmic variance terms. We focus on large scales (l<100) for which the shape
noise of the shear measurement becomes irrelevant and cosmic variance dominates
the error budget. For a modest degree of non-Gaussianity, fNL=+/-50,
modifications of the galaxy-galaxy lensing signal at the 10% level are seen on
scales R~300 Mpc, and grow rapidly toward larger scales as \propto R^2. We also
see a clear signature of the baryonic acoustic oscillation feature in the
matter power spectrum at ~150 Mpc, which can be measured by next-generation
lensing experiments. In addition we can probe the local-form primordial
non-Gaussianity in the galaxy-CMB lensing signal by correlating the lensing
potential reconstructed from CMB with high-z galaxies. For example, for
fNL=+/-50, we find that the galaxy-CMB lensing cross power spectrum is modified
by ~10% at l~40, and by a factor of two at l~10, for a population of galaxies
at z=2 with a bias of 2. The effect is greater for more highly biased
populations at larger z; thus, high-z galaxy surveys cross-correlated with CMB
offer a yet another probe of primordial non-Gaussianity.Comment: 21 pages, 30 figure
Comment on ``Solution of Classical Stochastic One-Dimensional Many-Body Systems''
In a recent Letter, Bares and Mobilia proposed the method to find solutions
of the stochastic evolution operator with a
non-trivial quartic term . They claim, ``Because of the conservation of
probability, an analog of the Wick theorem applies and all multipoint
correlation functions can be computed.'' Using the Wick theorem, they expressed
the density correlation functions as solutions of a closed set of
integro-differential equations.
In this Comment, however, we show that applicability of Wick theorem is
restricted to the case only.Comment: 1 page, revtex style, comment on paper Phys. Rev. Lett. {\bf 83},
5214 (1999
The first-mover advantage in scientific publication
Mathematical models of the scientific citation process predict a strong
"first-mover" effect under which the first papers in a field will, essentially
regardless of content, receive citations at a rate enormously higher than
papers published later. Moreover papers are expected to retain this advantage
in perpetuity -- they should receive more citations indefinitely, no matter how
many other papers are published after them. We test this conjecture against
data from a selection of fields and in several cases find a first-mover effect
of a magnitude similar to that predicted by the theory. Were we wearing our
cynical hat today, we might say that the scientist who wants to become famous
is better off -- by a wide margin -- writing a modest paper in next year's
hottest field than an outstanding paper in this year's. On the other hand,
there are some papers, albeit only a small fraction, that buck the trend and
attract significantly more citations than theory predicts despite having
relatively late publication dates. We suggest that papers of this kind, though
they often receive comparatively few citations overall, are probably worthy of
our attention.Comment: 7 pages, 3 figure
Rules for Computing Symmetry, Density and Stoichiometry in a Quasi-Unit-Cell Model of Quasicrystals
The quasi-unit cell picture describes the atomic structure of quasicrystals
in terms of a single, repeating cluster which overlaps neighbors according to
specific overlap rules. In this paper, we discuss the precise relationship
between a general atomic decoration in the quasi-unit cell picture atomic
decorations in the Penrose tiling and in related tiling pictures. Using these
relations, we obtain a simple, practical method for determining the density,
stoichiometry and symmetry of a quasicrystal based on the atomic decoration of
the quasi-unit cell taking proper account of the sharing of atoms between
clusters.Comment: 14 pages, 8 figure
A simple physical model for scaling in protein-protein interaction networks
It has recently been demonstrated that many biological networks exhibit a
scale-free topology where the probability of observing a node with a certain
number of edges (k) follows a power law: i.e. p(k) ~ k^-g. This observation has
been reproduced by evolutionary models. Here we consider the network of
protein-protein interactions and demonstrate that two published independent
measurements of these interactions produce graphs that are only weakly
correlated with one another despite their strikingly similar topology. We then
propose a physical model based on the fundamental principle that (de)solvation
is a major physical factor in protein-protein interactions. This model
reproduces not only the scale-free nature of such graphs but also a number of
higher-order correlations in these networks. A key support of the model is
provided by the discovery of a significant correlation between number of
interactions made by a protein and the fraction of hydrophobic residues on its
surface. The model presented in this paper represents the first physical model
for experimentally determined protein-protein interactions that comprehensively
reproduces the topological features of interaction networks. These results have
profound implications for understanding not only protein-protein interactions
but also other types of scale-free networks.Comment: 50 pages, 17 figure
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