6,417 research outputs found
Nonlinear Gravitational Clustering: dreams of a paradigm
We discuss the late time evolution of the gravitational clustering in an
expanding universe, based on the nonlinear scaling relations (NSR) which
connect the nonlinear and linear two point correlation functions. The existence
of critical indices for the NSR suggests that the evolution may proceed towards
a universal profile which does not change its shape at late times. We begin by
clarifying the relation between the density profiles of the individual halo and
the slope of the correlation function and discuss the conditions under which
the slopes of the correlation function at the extreme nonlinear end can be
independent of the initial power spectrum. If the evolution should lead to a
profile which preserves the shape at late times, then the correlation function
should grow as [in a universe] een at nonlinear scales. We
prove that such exact solutions do not exist; however, ther e exists a class of
solutions (``psuedo-linear profiles'', PLP's for short) which evolve as
to a good approximation. It turns out that the PLP's are the correlation
functions which arise if the individual halos are assumed to be isothermal
spheres. They are also configurations of mass in which the nonlinear effects of
gravitational clustering is a minimum and hence can act as building blocks of
the nonlinear universe. We discuss the implicatios of this result.Comment: 32 Pages, Submitted to Ap
The scale of homogeneity in the Las Campanas Redshift Survey
We analyse the Las Campanas Redshift Survey using the integrated conditional
density (or density of neighbors) in volume-limited subsamples up to
unprecedented scales (200 Mpc/) in order to determine without ambiguity the
behavior of the density field. We find that the survey is well described by a
fractal up to 20-30 Mpc/, but flattens toward homogeneity at larger scales.
Although the data are still insufficient to establish with high significance
the expected homogeneous behavior, and therefore to rule out a fractal trend to
larger scales, a fit with a CDM-like spectrum with high normalization well
represents the data.Comment: 8 pages, 3 figures, accepted on Ap.J. Letter
Attraction of Acorn-Infesting \u3ci\u3eCydia Latiferreana\u3c/i\u3e (Lepidoptera: Tortricidae) to Pheromone-Baited Traps
Males of acorn-infesting Cydia latiferreana are attracted to an equilibrium mixture of the four isomers of 8, 10-dodecadien-l-ol acetate, the virgin female-produced pheromone. Trap height relative to the height of trees in which traps are placed seems to be a significant factor influencing moth catches at attractant-baited traps. In an oak woodlot and in an oak nursery, catches of male moths were greater in traps placed near the upper periphery of the canopy than at traps deployed at lower levels in the tree. Practical application of pheromone-baited traps in a forest situation will require further study on lure formulation and on trap deployment under forest conditions
Amplitude and Phase Fluctuations for Gravitational Waves Propagating through Inhomogeneous Mass Distribution in the Universe
When a gravitational wave (GW) from a distant source propagates through the
universe, its amplitude and phase change due to gravitational lensing by the
inhomogeneous mass distribution. We derive the amplitude and phase
fluctuations, and calculate these variances in the limit of a weak
gravitational field of density perturbation. If the scale of the perturbation
is smaller than the Fresnel scale ( is the
GW frequency), the GW is not magnified due to the diffraction effect. The rms
amplitude fluctuation is for Hz, but it is reduced less
than 5% for a very low frequency of Hz. The rms phase
fluctuation in the chirp signal is radian at LISA frequency band
( Hz). Measurements of these fluctuations will provide
information about the matter power spectrum on the Fresnel scale pc.Comment: 6 pages, 6 figures, refferences added, accepted for publication in
Ap
Reionization Revisited: Secondary CMB Anisotropies and Polarization
Secondary CMB anisotropies and polarization provide a laboratory to study
structure formation in the reionized epoch. We consider the kinetic
Sunyaev-Zel'dovich effect from mildly nonlinear large-scale structure and show
that it is a natural extension of the perturbative Vishniac effect. If the gas
traces the dark matter to overdensities of order 10, as expected from
simulations, this effect is at least comparable to the Vishniac effect at
arcminute scales. On smaller scales, it may be used to study the thermal
history-dependent clustering of the gas. Polarization is generated through
Thomson scattering of primordial quadrupole anisotropies, kinetic (second order
Doppler) quadrupole anisotropies and intrinsic scattering quadrupole
anisotropies. Small scale polarization results from the density and ionization
modulation of these sources. These effects generically produce comparable E and
B-parity polarization, but of negligible amplitude (0.001-0.01 uK) in adiabatic
CDM models. However, the primordial and kinetic quadrupoles are observationally
comparable today so that a null detection of B-polarization would set
constraints on the evolution and coherence of the velocity field. Conversely, a
detection of a cosmological B-polarization even at large angles does not
necessarily imply the presence of gravity waves or vorticity. For these
calculations, we develop an all-sky generalization of the Limber equation that
allows for an arbitrary local angular dependence of the source for both scalar
and symmetric trace-free tensor fields on the sky.Comment: 14 pages, 12 figures, minor changes and typo fixes reflect published
versio
Power Spectrum Correlations Induced by Non-Linear Clustering
Gravitational clustering is an intrinsically non-linear process that
generates significant non-Gaussian signatures in the density field. We consider
how these affect power spectrum determinations from galaxy and weak-lensing
surveys. Non-Gaussian effects not only increase the individual error bars
compared to the Gaussian case but, most importantly, lead to non-trivial
cross-correlations between different band-powers. We calculate the
power-spectrum covariance matrix in non-linear perturbation theory (weakly
non-linear regime), in the hierarchical model (strongly non-linear regime), and
from numerical simulations in real and redshift space. We discuss the impact of
these results on parameter estimation from power spectrum measurements and
their dependence on the size of the survey and the choice of band-powers. We
show that the non-Gaussian terms in the covariance matrix become dominant for
scales smaller than the non-linear scale, depending somewhat on power
normalization. Furthermore, we find that cross-correlations mostly deteriorate
the determination of the amplitude of a rescaled power spectrum, whereas its
shape is less affected. In weak lensing surveys the projection tends to reduce
the importance of non-Gaussian effects. Even so, for background galaxies at
redshift z=1, the non-Gaussian contribution rises significantly around l=1000,
and could become comparable to the Gaussian terms depending upon the power
spectrum normalization and cosmology. The projection has another interesting
effect: the ratio between non-Gaussian and Gaussian contributions saturates and
can even decrease at small enough angular scales if the power spectrum of the
3D field falls faster than 1/k^2.Comment: 34 pages, 15 figures. Revised version, includes a clearer explanation
of why the hierarchical ansatz does not provide a good model of the
covariance matrix in the non-linear regime, and new constraints on the
amplitudes Ra and Rb for general 4-pt function configurations in the
non-linear regim
Correlation between the Mean Matter Density and the Width of the Saturated Lyman Alpha Absorption
We report a scaling of the mean matter density with the width of the
saturated Lyman alpha absorptions. This property is established using the
``pseudo-hydro'' technique (Croft et al. 1998). It provides a constraint for
the inversion of the Lyman alpha forest, which encounters difficulty in the
saturated region. With a Gaussian density profile and the scaling relation, a
simple inversion of the simulated Lyman alpha forests shows that the
one-dimensional mass power spectrum is well recovered on scales above 2 Mpc/h,
or roughly k < 0.03 s/km, at z=3. The recovery underestimates the power on
small scales, but improvement is possible with a more sophisticated algorithm.Comment: 7 pages, 9 figures, accepted for publication in MNRAS, replaced by
the version after proo
Cluster Correlation in Mixed Models
We evaluate the dependence of the cluster correlation length r_c on the mean
intercluster separation D_c, for three models with critical matter density,
vanishing vacuum energy (Lambda = 0) and COBE normalized: a tilted CDM (tCDM)
model (n=0.8) and two blue mixed models with two light massive neutrinos
yielding Omega_h = 0.26 and 0.14 (MDM1 and MDM2, respectively). All models
approach the observational value of sigma_8 (and, henceforth, the observed
cluster abundance) and are consistent with the observed abundance of Damped
Lyman_alpha systems. Mixed models have a motivation in recent results of
neutrino physics; they also agree with the observed value of the ratio
sigma_8/sigma_25, yielding the spectral slope parameter Gamma, and nicely fit
LCRS reconstructed spectra. We use parallel AP3M simulations, performed in a
wide box (side 360/h Mpc) and with high mass and distance resolution, enabling
us to build artificial samples of clusters, whose total number and mass range
allow to cover the same D_c interval inspected through APM and Abell cluster
clustering data. We find that the tCDM model performs substantially better than
n=1 critical density CDM models. Our main finding, however, is that mixed
models provide a surprisingly good fit of cluster clustering data.Comment: 22 pages + 10 Postscript figures. Accepted for publication in Ap
A technique for correcting ERTS data for solar and atmospheric effects
The author has identified the following significant results. Based on processing ERTS CCTs and ground truth measurements collected on Michigan test site for January through June 1973 the following results are reported: (1) atmospheric transmittance varies from: 70 to 85% in band 4, 77 to 90% in band 5, 80 to 94% in band 6, and 84 to 97% in band 7 for one air mass; (2) a simple technique was established to determine atmospheric scattering seen by ERTS-1 from ground-based measurements of sky radiance. For March this scattering was found to be equivalent to that produced by a target having a reflectance of 11% in band 4, 5% in band 5, 3% in band 6, and 1% in band 7; (3) computer ability to classify targets under various atmospheric conditions was determined. Classification accuracy on some targets (i.e. bare soil, tended grass, etc.) hold up even under the most severe atmospheres encountered, while performance on other targets (trees, urban, rangeland, etc.) degrades rapidly when atmospheric conditions change by the smallest amount
A Closure Theory for Non-linear Evolution of Cosmological Power Spectra
We apply a non-linear statistical method in turbulence to the cosmological
perturbation theory and derive a closed set of evolution equations for matter
power spectra. The resultant closure equations consistently recover the
one-loop results of standard perturbation theory and beyond that, it is still
capable of treating the non-linear evolution of matter power spectra. We find
the exact integral expressions for the solutions of closure equations. These
analytic expressions coincide with the renormalized one-loop results presented
by Crocce & Scoccimarro (2006,2007). By constructing the non-linear propagator,
we analytically evaluate the non-linear matter power spectra based on the
first-order Born approximation of the integral expressions and compare it with
those of the renormalized perturbation theory.Comment: 22 pages, 4 figures, accepted for publication in Ap
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