16,476 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
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
Search for Cosmic Strings in CMB Anisotropies
We have searched the 1st-year WMAP W-Band CMB anisotropy map for evidence of
cosmic strings. We have set a limit of at 95% CL for statistical search for a significant number of strings
in the map. We also have set a limit using the uniform distribution of strings
model in the WMAP data with
at 95% CL. And the pattern search technique we developed here set a limit
at 95% CL.Comment: 10 pages, 8 postscript figure
The Validity of the Cosmic String Pattern Search with the Cosmic Microwave Background
We introduce a new technique to detect the discrete temperature steps that
cosmic strings might have left in the cosmic microwave background (CMB)
anisotropy map. The technique provides a validity test on the pattern search of
cosmic strings that could serve as the groundwork for future pattern searches.
The detecting power of the technique is only constrained by two unavoidable
features of CMB data: (1) the finite pixelization of the sky map and (2) the
Gaussian fluctuation from instrumental noise and primordial anisotropy. We set
the upper limit on the cosmic string parameter as at the 95% confidence level (CL) and find that the amplitude of the
temperature step has to be greater than in order to be detected for
the {\it{Wilkinson Microwave Anisotropy Probe (WMAP)}} 3 year data.Comment: 9 pages, 3 figures. Revised for publicatio
Oxidation States of Graphene: Insights from Computational Spectroscopy
When it is oxidized, graphite can be easily exfoliated forming graphene oxide
(GO). GO is a critical intermediate for massive production of graphene, and it
is also an important material with various application potentials. With many
different oxidation species randomly distributed on the basal plane, GO has a
complicated nonstoichiometric atomic structure that is still not well
understood in spite of of intensive studies involving many experimental
techniques. Controversies often exist in experimental data interpretation. We
report here a first principles study on binding energy of carbon 1s orbital in
GO. The calculated results can be well used to interpret experimental X-ray
photoelectron spectroscopy (XPS) data and provide a unified spectral
assignment. Based on the first principles understanding of XPS, a GO structure
model containing new oxidation species epoxy pair and epoxy-hydroxy pair is
proposed. Our results demonstrate that first principles computational
spectroscopy provides a powerful means to investigate GO structure.Comment: accepted by J. Chem. Phy
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
Numerical test of the damping time of layer-by-layer growth on stochastic models
We perform Monte Carlo simulations on stochastic models such as the
Wolf-Villain (WV) model and the Family model in a modified version to measure
mean separation between islands in submonolayer regime and damping time
of layer-by-layer growth oscillations on one dimension. The
stochastic models are modified, allowing diffusion within interval upon
deposited. It is found numerically that the mean separation and the damping
time depend on the diffusion interval , leading to that the damping time is
related to the mean separation as for the WV model
and for the Family model. The numerical results are in
excellent agreement with recent theoretical predictions.Comment: 4 pages, source LaTeX file and 5 PS figure
Unified entropy, entanglement measures and monogamy of multi-party entanglement
We show that restricted shareability of multi-qubit entanglement can be fully
characterized by unified- entropy. We provide a two-parameter class of
bipartite entanglement measures, namely unified- entanglement with its
analytic formula in two-qubit systems for , and
. Using unified- entanglement, we establish a broad class of
the monogamy inequalities of multi-qubit entanglement for , and .Comment: 17 pages, 1 figur
Determination of from Gross-Llewellyn Smith sum rule by accounting for infrared renormalon
We recapitulate the method which resums the truncated perturbation series of
a physical observable in a way which takes into account the structure of the
leading infrared renormalon. We apply the method to the Gross-Llewellyn Smith
(GLS) sum rule. By confronting the obtained result with the experimentally
extracted GLS value, we determine the value of the QCD coupling parameter which
turns out to agree with the present world average.Comment: invited talk by G.C. in WG3 of NuFact02, July 1-6, 2002, London; 4
pages, revte
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