2,123 research outputs found
Optimal strategy for polarization modulation in the LSPE-SWIPE experiment
Context. Cosmic microwave background (CMB) B-mode experiments are required to control systematic effects with an unprecedented level of accuracy. Polarization modulation by a half wave plate (HWP) is a powerful technique able to mitigate a large number of the instrumental systematics. Aims. Our goal is to optimize the polarization modulation strategy of the upcoming LSPE-SWIPE balloon-borne experiment, devoted to the accurate measurement of CMB polarization at large angular scales. Methods. We departed from the nominal LSPE-SWIPE modulation strategy (HWP stepped every 60 s with a telescope scanning at around 12 deg/s) and performed a thorough investigation of a wide range of possible HWP schemes (either in stepped or continuously spinning mode and at different azimuth telescope scan-speeds) in the frequency, map and angular power spectrum domain. In addition, we probed the effect of high-pass and band-pass filters of the data stream and explored the HWP response in the minimal case of one detector for one operation day (critical for the single-detector calibration process). We finally tested the modulation performance against typical HWP-induced systematics. Results. Our analysis shows that some stepped HWP schemes, either slowly rotating or combined with slow telescope modulations, represent poor choices. Moreover, our results point out that the nominal configuration may not be the most convenient choice. While a large class of spinning designs provides comparable results in terms of pixel angle coverage, map-making residuals and BB power spectrum standard deviations with respect to the nominal strategy, we find that some specific configurations (e.g., a rapidly spinning HWP with a slow gondola modulation) allow a more efficient polarization recovery in more general real-case situations. Conclusions. Although our simulations are specific to the LSPE-SWIPE mission, the general outcomes of our analysis can be easily generalized to other CMB polarization experiments
Development of Lumped Element Kinetic Inductance Detectors for the W-Band
We are developing a Lumped Element Kinetic Inductance Detector (LEKID) array
able to operate in the W-band (75-110 GHz) in order to perform ground-based
Cosmic Microwave Background (CMB) and mm-wave astronomical observations. The
W-band is close to optimal in terms of contamination of the CMB from Galactic
synchrotron, free-free, and thermal interstellar dust. In this band, the
atmosphere has very good transparency, allowing interesting ground-based
observations with large (>30 m) telescopes, achieving high angular resolution
(<0.4 arcmin). In this work we describe the startup measurements devoted to the
optimization of a W-band camera/spectrometer prototype for large aperture
telescopes like the 64 m SRT (Sardinia Radio Telescope). In the process of
selecting the best superconducting film for the LEKID, we characterized a 40 nm
thick Aluminum 2-pixel array. We measured the minimum frequency able to break
CPs (i.e. ) obtaining
GHz, that corresponds to a critical temperature of 1.31 K. This is not suitable
to cover the entire W-band. For an 80 nm layer the minimum frequency decreases
to 93.2 GHz, which corresponds to a critical temperature of 1.28 K; this value
is still suboptimal for W-band operation. Further increase of the Al film
thickness results in bad performance of the detector. We have thus considered a
Titanium-Aluminum bi-layer (10 nm thick Ti + 25 nm thick Al, already tested in
other laboratories), for which we measured a critical temperature of 820 mK and
a cut-on frequency of 65 GHz: so this solution allows operation in the entire
W-band.Comment: 16th International Workshop on Low Temperature Detectors, Grenoble
20-24 July 2015, Journal of Low Temperature Physics, Accepte
Elliptic CMB Sky
The ellipticity of the anisotropy spots of the Cosmic Microwave Background
measured by the Wilkinson Microwave Anisotropy Probe (WMAP) has been studied.
We find an average ellipticity of about 2, confirming with a far larger
statistics similar results found first for the COBE-DMR CMB maps, and then for
the BOOMERanG CMB maps. There are no preferred directions for the obliquity of
the anisotropy spots. The average ellipticity is independent of temperature
threshold and is present on scales both smaller and larger than the horizon at
the last scattering. The measured ellipticity characteristics are consistent
with being the effect of geodesics mixing occurring in an hyperbolic Universe,
and can mark the emergence of CMB ellipticity as a new observable constant
describing the Universe. There is no way of simulating this effect. Therefore
we cannot exclude that the observed behavior of the measured ellipticity can
result from a trivial topology in the popular flat -CDM model, or from
a non-trivial topology.Comment: 10 pages, 5 figures, the version to appear in Mod.Phys.Lett.
Using the acoustic peak to measure cosmological parameters
Recent measurements of the cosmic microwave background radiation by the
Boomerang experiment indicate that the universe is spatially flat. Here some
simple back-of-the-envelope calculations are used to explain their result. The
main result is a simple formula for the angular scale of the acoustic peak in
terms of the standard cosmological parameters:
l=193*[1+3(1-Omega_0)/5+(1-h)/5+Omega_Lambda/35].Comment: 4 pages, 1 figure, Explanations have been clarifie
Modified Chaplygin Traversable Wormholes
The modified Chaplygin gas (MCG) is a strong candidate for the unified model
of dark matter and dark energy. The equation of state of this modified model is
valid from the radiation era to the CDM model. In early epoch (when
was large), dark matter had the dominant role while at later stages
(when is small), the MCG model behaves as dark energy. In this work, we
have found exact solution of static spherically symmetric Einstein equations
describing a wormhole for an inhomogeneous distribution of modified Chaplygin
gas. For existence of wormhole solution, there are some restrictions relating
the parameters in the equation of state for MCG and the throat radius of the
wormhole. Physical properties and characteristics of these modified Chaplygin
wormholes are analyzed in details.Comment: 9 pages, 1 figur
Mineral profile grassland of Andropogon lateralis and Sorghastrum setosum (Gramineae) in Corrientes, Argentina
El objetivo de este trabajo fue determinar la composición florística y el aporte de
minerales a la dieta animal para la producción de carne bovina de los pastizales de
Andropogon lateralis Nees (PAL) y Sorghastrum setosun (Griseb.) Hitchc. (PSS), analizados
mediante espectrometría ICP-AES en dos series de suelo de la provincia de Corrientes,
Argentina. El mayor aporte de materia seca lo realizan A. lateralis y S. setosum. El aporte
de leguminosas es bajo. El perfil de elementos minerales esenciales, probablemente
esenciales y los de función incierta, cubren parcialmente los requerimientos del ganado
bovino productor de carne, excepto para Mn. Las relaciones entre elementos, Ca/P, Na/K
(mEq), Cu/Mo y Cu/Fe son aceptables. Las relaciones K/Mg, K/Ca+Mg (mEq) y Na/Mg
(mEq) no son adecuadas, pues existe deficiencia de Mg.The goal of this work was to determine the floristic composition and the mineral
contribution of Andropogon lateralis Nees (PAL) and Sorghastrum setosum (PSS)
pastures, in the animal diet for the production of beef, analyzed by ICP-AES spectrometry
in two series of soils from the Province of Corrientes, Argentina. The greatest contribution
of dry raw matter is provided by A. lateralis and S. setosum. The contribution of
legume is low. The profile of essential mineral elements, probably essential ones and
of those of uncertain function, partially fulfill the meat producer cattle requirements.
The elemental ratios Ca/P, Na/K (mEq), Cu/Mo and Cu/Fe, are acceptable. The K/Mg,
K/Ca+Mg (mEq) and Na/Mg (mEq) ratios are not adequate, and there is Mg deficiency.Fil: Bernardis, Aldo C..
Universidad Nacional del Nordeste. Facultad de Ciencias AgrariasFil: Villafañe, Roxana.
Consejo Nacional de Investigaciones Científicas y TécnicasFil: Pellerano, Roberto G..
Universidad Nacional del NordesteFil: Marchevky, Eduardo.
Universidad Nacional de San Luis. Facultad de Química,
Bioquímica y Farmacia. Departamento de Química
Self interacting Brans Dicke cosmology and Quintessence
Recent cosmological observations reveal that we are living in a flat
accelerated expanding universe. In this work we have investigated the nature of
the potential compatible with the power law expansion of the universe in a self
interacting Brans Dicke cosmology with a perfect fluid background and have
analyzed whether this potential supports the accelerated expansion. It is found
that positive power law potential is relevant in this scenario and can drive
accelerated expansion for negative Brans Dicke coupling parameter . The
evolution of the density perturbation is also analyzed in this scenerio and is
seen that the model allows growing modes for negative .Comment: 8pages, 5 figures, PRD style, some changes are made, figures added,
reference added. To be published in Int. J. Mod. Phys.
Digital Deblurring of CMB Maps II: Asymmetric Point Spread Function
In this second paper in a series dedicated to developing efficient numerical
techniques for the deblurring Cosmic Microwave Background (CMB) maps, we
consider the case of asymmetric point spread functions (PSF). Although
conceptually this problem is not different from the symmetric case, there are
important differences from the computational point of view because it is no
longer possible to use some of the efficient numerical techniques that work
with symmetric PSFs. We present procedures that permit the use of efficient
techniques even when this condition is not met. In particular, two methods are
considered: a procedure based on a Kronecker approximation technique that can
be implemented with the numerical methods used with symmetric PSFs but that has
the limitation of requiring only mildly asymmetric PSFs. The second is a
variant of the classic Tikhonov technique that works even with very asymmetric
PSFs but that requires discarding the edges of the maps. We provide details for
efficient implementations of the algorithms. Their performance is tested on
simulated CMB maps.Comment: 9 pages, 13 Figure
Delayed Recombination and Standard Rulers
Measurements of Baryonic Acoustic Oscillations in galaxy surveys have been
recognized as a powerful tool for constraining dark energy. However, this
method relies on the knowledge of the size of the acoustic horizon at
recombination derived from Cosmic Microwave Background Anisotropy measurements.
This estimate is typically derived assuming a standard recombination scheme;
additional radiation sources can delay recombination altering the cosmic
ionization history and the cosmological inferences drawn from CMB and BAO data.
In this paper we quantify the effect of delayed recombination on the
determination of dark energy parameters from future BAO surveys such as BOSS
and WFMOS. We find the impact to be small but still not negligible. In
particular, if recombination is non-standard (to a level still allowed by CMB
data), but this is ignored, future surveys may incorrectly suggest the presence
of a redshift dependent dark energy component. On the other hand, in the case
of delayed recombination, adding to the analysis one extra parameter describing
deviations from standard recombination, does not significantly degrade the
error-bars on dark energy parameters and yields unbiased estimates.Comment: 8 pages, 5 figure
Ellipticity in Cosmic Microwave Background as a Tracer of Large-Scale Universe
Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data confirm the
ellipticity of anisotropies of Cosmic Microwave Background (CMB) maps, found
previously for Boomerang and WMAP 1-year high sensitivity maps. The low noise
level of the WMAP latter data enable also to show that, the ellipticity is a
property not described by the conventional cosmological model fitting the power
spectrum of CMB. As a large scale anomaly, the ellipticity characteristics are
consistent with the effect of geodesics mixing occurring in hyperbolic
Universe. Its relation to other large scale effects, i.e. to suppressed low
multipoles, as well as to dark energy if the latter is due to vacuum
fluctuations, is then an arising issue.Comment: to appear in Phys. Lett.
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