139 research outputs found
Large Scale Pressure Fluctuations and Sunyaev-Zel'dovich Effect
The Sunyaev-Zel'dovich (SZ) effect associated with pressure fluctuations of
the large scale structure gas distribution will be probed with current and
upcoming wide-field small angular scale cosmic microwave background
experiments. We study the generation of pressure fluctuations by baryons which
are present in virialized dark matter halos and by baryons present in small
overdensities. For collapsed halos, assuming the gas distribution is in
hydrostatic equilibrium with matter density distribution, we predict the
pressure power spectrum and bispectrum associated with the large scale
structure gas distribution by extending the dark matter halo approach which
describes the density field in terms of correlations between and within halos.
The projected pressure power spectrum allows a determination of the resulting
SZ power spectrum due to virialized structures. The unshocked photoionized
baryons present in smaller overdensities trace the Jeans-scale smoothed dark
matter distribution. They provide a lower limit to the SZ effect due to large
scale structure in the absence of massive collapsed halos. We extend our
calculations to discuss higher order statistics, such as bispectrum and
skewness in SZ data. The SZ-weak lensing cross-correlation is suggested as a
probe of correlations between dark matter and baryon density fields, while the
probability distribution functions of peak statistics of SZ halos in wide field
CMB data can be used as a probe of cosmology and non-Gaussian evolution of
large scale structure pressure fluctuations.Comment: 16 pages, 9 figures; Revised with expanded discussions. Phys. Rev. D.
(in press
Optimal limits on f_{NL}^{local} from WMAP 5-year data
We have applied the optimal estimator for f_{NL}^{local} to the 5 year WMAP
data. Marginalizing over the amplitude of foreground templates we get -4 <
f_{NL}^{local} < 80 at 95% CL. Error bars of previous (sub-optimal) analyses
are roughly 40% larger than these. The probability that a Gaussian simulation,
analyzed using our estimator, gives a result larger in magnitude than the one
we find is 7%. Our pipeline gives consistent results when applied to the three
and five year WMAP data releases and agrees well with the results from our own
sub-optimal pipeline. We find no evidence of any residual foreground
contamination.Comment: [v1] 21 pages, 7 figures. [v2] minor changes matching published
versio
Constraining the dark energy dynamics with the cosmic microwave background bispectrum
We consider the influence of the dark energy dynamics at the onset of cosmic
acceleration on the Cosmic Microwave Background (CMB) bispectrum, through the
weak lensing effect induced by structure formation. We study the line of sight
behavior of the contribution to the bispectrum signal at a given angular
multipole : we show that it is non-zero in a narrow interval centered at a
redshift satisfying the relation , where the
wavenumber corresponds to the scale entering the non-linear phase, and is
the cosmological comoving distance. The relevant redshift interval is in the
range 0.1\lsim z\lsim 2 for multipoles 1000\gsim\ell\gsim 100; the signal
amplitude, reflecting the perturbation dynamics, is a function of the
cosmological expansion rate at those epochs, probing the dark energy equation
of state redshift dependence independently on its present value. We provide a
worked example by considering tracking inverse power law and SUGRA Quintessence
scenarios, having sensibly different redshift dynamics and respecting all the
present observational constraints. For scenarios having the same present
equation of state, we find that the effect described above induces a projection
feature which makes the bispectra shifted by several tens of multipoles, about
10 times more than the corresponding effect on the ordinary CMB angular power
spectrum.Comment: 15 pages, 7 figures, matching version accepted by Physical Review D,
one figure improve
Inflation in Realistic D-Brane Models
We find successful models of D-brane/anti-brane inflation within a string
context. We work within the GKP-KKLT class of type IIB string vacua for which
many moduli are stabilized through fluxes, as recently modified to include
`realistic' orbifold sectors containing standard-model type particles. We allow
all moduli to roll when searching for inflationary solutions and find that
inflation is not generic inasmuch as special choices must be made for the
parameters describing the vacuum. But given these choices inflation can occur
for a reasonably wide range of initial conditions for the brane and antibrane.
We find that D-terms associated with the orbifold blowing-up modes play an
important role in the inflationary dynamics. Since the models contain a
standard-model-like sector after inflation, they open up the possibility of
addressing reheating issues. We calculate predictions for the CMB temperature
fluctuations and find that these can be consistent with observations, but are
generically not deep within the scale-invariant regime and so can allow
appreciable values for as well as predicting a potentially
observable gravity-wave signal. It is also possible to generate some admixture
of isocurvature fluctuations.Comment: 39 pages, 21 figures; added references; identified parameters
combining successful inflation with strong warping, as needed for consistency
of the approximation
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Cichlid biogeography: comment and review
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72313/1/j.1467-2979.2004.00148.x.pd
The Tonigala granite, N. W. Ceylon
A pink, microcline granite at Tonigala in north-western Ceylon occurs as a concordant sheet, one to two miles wide and about 10 miles long, in a complex of migmatitic and granitic biotite and biotite-hornblende gneisses belonging to the PreCambrian Vijayan Series. The granite is composed of quartz, microcline-microperthite, subordinate oligoclase, and biotite. It is traversed by an anastomosing system of veins of red granite and by dykes, veins and patches of pegmatite, aplite, and microgranite. A parallel swarm of pre-granitic dykes is also present. Enclaves of biotite schist in the form of lenses, bands, and foliae are found within the granite, and corrugations of thin biotitic foliae with a constant axial direction and plunge are scattered throughout. Field and petrographic evidence suggests that the Tonigala granite was formed by microclinisation of pre-existing synkinematic rocks, possibly granodioritic in composition. In its petrochemistry the granite resembles in many respects the late-kinematic granites of Finland and West Africa, but in certain other important characteristics it is similar to the synkinematic granites of Finland. It is thought that the Tonigala granite acquired its late-kinematic character by metasomatism
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