13,482 research outputs found
Studies of CMB structure at Dec=40. II: Analysis and cosmological interpretation
We present a detailed analysis of the cosmic microwave background structure
in the Tenerife Dec=+40 degrees data. The effect of local atmospheric
contributions on the derived fluctuation amplitude is considered, resulting in
an improved separation of the intrinsic CMB signal from noise. Our analysis
demonstrates the existence of common structure in independent data scans at 15
and 33 GHz. For the case of fluctuations described by a Gaussian
auto-correlation function, a likelihood analysis of our combined results at 15
and 33 GHz implies an intrinsic rms fluctuation level of 48^{+21}_{-15} uK on a
coherence scale of 4 degrees; the equivalent analysis for a
Harrison-Zel'dovitch model gives a power spectrum normalisation of Q_{rms-ps} =
22^{+10}_{-6} uK. The fluctuation amplitude is seen to be consistent at the 68%
confidence level with that reported for the COBE two-year data for primordial
fluctuations described by a power law model with a spectral index in the range
1.0 \le n \le 1.6. This limit favours the large scale CMB anisotropy being
dominated by scalar fluctuations rather than tensor modes from a gravitational
wave background. The large scale Tenerife and COBE results are considered in
conjunction with observational results from medium scale experiments in order
to place improved limits on the fluctuation spectral index; we find n=1.10 +/-
0.10 assuming standard CDM with H_{0}=50 kms^{-1}Mpc^{-1}.Comment: 10 pages LaTeX, including 8 PostScript figures. Accepted for
publication in MNRA
Avaliação do lençol freático em duas áreas exploradas com a cultura do coqueiro (Cocos nucifera L.).
bitstream/item/90507/1/CPATC-PESQ.-AND.-36-86.pd
Markov Chain Beam Randomization: a study of the impact of PLANCK beam measurement errors on cosmological parameter estimation
We introduce a new method to propagate uncertainties in the beam shapes used
to measure the cosmic microwave background to cosmological parameters
determined from those measurements. The method, which we call Markov Chain Beam
Randomization, MCBR, randomly samples from a set of templates or functions that
describe the beam uncertainties. The method is much faster than direct
numerical integration over systematic `nuisance' parameters, and is not
restricted to simple, idealized cases as is analytic marginalization. It does
not assume the data are normally distributed, and does not require Gaussian
priors on the specific systematic uncertainties. We show that MCBR properly
accounts for and provides the marginalized errors of the parameters. The method
can be generalized and used to propagate any systematic uncertainties for which
a set of templates is available. We apply the method to the Planck satellite,
and consider future experiments. Beam measurement errors should have a small
effect on cosmological parameters as long as the beam fitting is performed
after removal of 1/f noise.Comment: 17 pages, 23 figures, revised version with improved explanation of
the MCBR and overall wording. Accepted for publication in Astronomy and
Astrophysics (to appear in the Planck pre-launch special issue
Absolute Calibration of the Radio Astronomy Flux Density Scale at 22 to 43 GHz Using Planck
The Planck mission detected thousands of extragalactic radio sources at
frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense
that it is based on the satellite's annual motion around the Sun and the
temperature of the cosmic microwave background), and its beams are well
characterized at sub-percent levels. Thus Planck's flux density measurements of
compact sources are absolute in the same sense. We have made coordinated VLA
and ATCA observations of 65 strong, unresolved Planck sources in order to
transfer Planck's calibration to ground-based instruments at 22, 28, and 43
GHz. The results are compared to microwave flux density scales currently based
on planetary observations. Despite the scatter introduced by the variability of
many of the sources, the flux density scales are determined to 1-2% accuracy.
At 28 GHz, the flux density scale used by the VLA runs 3.6% +- 1.0% below
Planck values; at 43 GHz, the discrepancy increases to 6.2% +- 1.4% for both
ATCA and the VLA.Comment: 16 pages, 4 figures and 4 table
Small-Angle CMB Temperature Anisotropies Induced by Cosmic Strings
We use Nambu-Goto numerical simulations to compute the cosmic microwave
background (CMB) temperature anisotropies induced at arcminute angular scales
by a network of cosmic strings in a Friedmann-Lemaitre-Robertson-Walker (FLRW)
expanding universe. We generate 84 statistically independent maps on a 7.2
degree field of view, which we use to derive basic statistical estimators such
as the one-point distribution and two-point correlation functions. At high
multipoles, the mean angular power spectrum of string-induced CMB temperature
anisotropies can be described by a power law slowly decaying as \ell^{-p}, with
p=0.889 (+0.001,-0.090) (including only systematic errors). Such a behavior
suggests that a nonvanishing string contribution to the overall CMB
anisotropies may become the dominant source of fluctuations at small angular
scales. We therefore discuss how well the temperature gradient magnitude
operator can trace strings in the context of a typical arcminute
diffraction-limited experiment. Including both the thermal and nonlinear
kinetic Sunyaev-Zel'dovich effects, the Ostriker-Vishniac effect, and the
currently favored adiabatic primary anisotropies, we find that, on such a map,
strings should be ``eye visible,'' with at least of order ten distinctive
string features observable on a 7.2 degree gradient map, for tensions U down to
GU \simeq 2 x 10^{-7} (in Planck units). This suggests that, with upcoming
experiments such as the Atacama Cosmology Telescope (ACT), optimal
non-Gaussian, string-devoted statistical estimators applied to small-angle CMB
temperature or gradient maps may put stringent constraints on a possible cosmic
string contribution to the CMB anisotropies.Comment: 17 pages, 9 figures. v2: matches published version, minor
clarifications added, typo in Eq. (8) fixed, results unchange
Fermionic dark matter-photon quantum interaction: A mechanism for darkness
ELKO fermionic fields are prime candidates to describe dark matter, due to
their intrinsic neutral nature, as they are constructed as eigenstates of the
charge conjugation operator with dual helicity. To formulate the meaning of the
darkness, the ELKO-photon coupling is scrutinized with a Pauli-like
interaction, and the path integral is then formulated from the phase space
constraint structure. Ward-Takahashi-like identities and Schwinger-Dyson
equations, together with renormalizability, are employed to investigate a
phenomenological mechanism to avoid external light signals. Accordingly, the
non-polarized pair annihilation and Compton-like processes are shown to vanish
at the limit of small scattering angles even if considering 1-loop radiative
corrections, reinforcing the ELKO dark matter interpretation. However, ELKO
interactions with nucleons are still possible. Motivated by recent
nucleon-recoil experiments to detect dark matter, we furnish a consistent
theoretical setup to describe ELKO-photon interaction compatible with the
prevalence of darkness.Comment: 42 pages, 6 figure
The distance to the LMC cluster NGC 1866 and the surrounding field
We use the Main Sequence stars in the LMC cluster NGC 1866 and of Red Clump
stars in the local field to obtain two independent estimates of the LMC
distance. We apply an empirical Main Sequence-fitting technique based on a
large sample of subdwarfs with accurate {\sl Hipparcos} parallaxes in order to
estimate the cluster distance modulus, and the multicolor Red Clump method to
derive distance and reddening of the LMC field. We find that the Main
Sequence-fitting and the Red Clump distance moduli are in significant
disagreement; NGC 1866 distance is equal to 0.08 (consistent with a previous estimate using the same data
and theoretical Main Sequence isochrones), while the field stars provide 0.07. This difference reflects the more general
dichotomy in the LMC distance estimates found in the literature. Various
possible causes for this disagreement are explored, with particular attention
paid to the still uncertain metallicity of the cluster and the star formation
history of the field stars.Comment: 5 pages, incl. 1 figure, uses emulateapj.sty, ApJ accepte
Magnetic Fields of Spherical Compact Stars in Braneworld
We study the dipolar magnetic field configuration in dependence on brane
tension and present solutions of Maxwell equations in the internal and external
background spacetime of a magnetized spherical star in a Randall-Sundrum II
type braneworld. The star is modelled as sphere consisting of perfect highly
magnetized fluid with infinite conductivity and frozen-in dipolar magnetic
field. With respect to solutions for magnetic fields found in the Schwarzschild
spacetime brane tension introduces enhancing corrections both to the interior
and the exterior magnetic field. These corrections could be relevant for the
magnetic fields of magnetized compact objects as pulsars and magnetars and may
provide the observational evidence for the brane tension through the
modification of formula for magneto-dipolar emission which gives amplification
of electromagnetic energy loss up to few orders depending on the value of the
brane tension.Comment: 11 pages, 5 figures, 1 tabl
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