391 research outputs found
Reconstruction of -attractor supergravity models of inflation
In this paper, we apply reconstruction techniques to recover the potential
parameters for a particular class of single-field models, the
-attractor (supergravity) models of inflation. This also allows to
derive the inflaton vacuum expectation value at horizon crossing. We show how
to use this value as one of the input variables to constrain the
postaccelerated inflationary phase. We assume that the tensor-to-scalar ratio
is of the order of , a level reachable by the expected
sensitivity of the next-generation CMB experiments.Comment: 10 pages, LaTeX, some typos correcte
Constraining auto-interaction terms in α-attractor supergravity models of inflation
The inflationary mechanism has become the paradigm of modern cosmology over the last thirty years. However, there are several aspects of inflationary physics that are still to be addressed, like the shape of the inflationary potential. Regarding this, the so-called α-attractor models show interesting properties. In this work, the reconstruction of the effective potential around the global minimum of these particular potentials is provided, assuming a detection of permille-order for the tensor-to-scalar-ratio by forthcoming cosmic microwave background or gravitational waves experiments
CMB Polarization: Scientific Case and Data Analysis Issues
We review the science case for studying CMB polarization. We then discuss the
main issues related to the analysis of forth-coming polarized CMB data, such as
those expected from balloon-borne (e.g. BOOMERanG) and satellite (e.g. Planck)
experiments.Comment: 6 pages, 4 figures. To appear in "Astrophysical Polarized Background"
Workshop Proceedings, eds. S. Cecchini, S. Cortiglioni, R. Sault and C.
Sbarra, AIP, in pres
Forecasting isocurvature models with CMB lensing information: axion and curvaton scenarios
Some inflationary models predict the existence of isocurvature primordial
fluctuations, in addition to the well known adiabatic perturbation. Such mixed
models are not yet ruled out by available data sets. In this paper we explore
the possibility of obtaining better constraints on the isocurva- ture
contribution from future astronomical data. We consider the axion and curvaton
inflationary scenarios, and use Planck satellite experimental specifications
together with SDSS galaxy survey to forecast for the best parameter error
estimation by means of the Fisher information matrix formal- ism. In
particular, we consider how CMB lensing information can improve this forecast.
We found substantial improvements for all the considered cosmological
parameters. In the case of isocurvature amplitude this improvement is strongly
model dependent, varying between less than 1% and above 20% around its fiducial
value. Furthermore, CMB lensing enables the degeneracy break between the
isocurvature amplitude and correlation phase in one of the models. In this
sense, CMB lensing information will be crucial in the analysis of future data.Comment: Accepted for publication in PR
Spherical Needlets for CMB Data Analysis
We discuss Spherical Needlets and their properties. Needlets are a form of
spherical wavelets which do not rely on any kind of tangent plane approximation
and enjoy good localization properties in both pixel and harmonic space;
moreover needlets coefficients are asymptotically uncorrelated at any fixed
angular distance, which makes their use in statistical procedures very
promising. In view of these properties, we believe needlets may turn out to be
especially useful in the analysis of Cosmic Microwave Background (CMB) data on
the incomplete sky, as well as of other cosmological observations. As a final
advantage, we stress that the implementation of needlets is computationally
very convenient and may rely completely on standard data analysis packages such
as HEALPix.Comment: 7 pages, 7 figure
Potential sources of particulate iron in surface and deep waters of the terra nova bay (Ross sea, antarctica)
The distribution of particulate Fe (pFe), suspended particulate matter (SPM), and other particulate trace metals were investigated in Terra Nova Bay as part of CDW Effects on glaciaL mElting and on Bulk of Fe in the Western Ross sea (CELEBeR) and Plankton biodiversity and functioning of the Ross Sea ecosystems in a changing Southern Ocean (P-ROSE) projects. Variable concentrations of SPM (0.09–97 mg L−1 ), pFe (0.51–8.70 nM) and other trace metals were found in the Antarctic Surface waters (AASW) layer, where the addition of meltwater contributed to the pool with both lithogenic and biogenic forms. The deeper layer of the water column was occupied by High Salinity Shelf Water (HSSW) and Terra Nova Bay Ice Shelf Water (TISW) encompassing glacial water as confirmed by the lightest δ18 O measured values. The concentration of pFe in TISW (11.7 ± 9.2 nM) was higher than in HSSW samples (5.55 ± 4.43 nM), suggesting that the drainage of material released from glaciers surrounding the area is relevant in terms of pFe contribution. Particulate Fe/Al and Mn/Al ratios were substantially in excess compared with the mean crustal ratios. Microscopic analyses confirmed that more labile Fe oxyhydroxides and authigenic MnO2 phases were present together with biogenic sinking material. Future expected increasing melt rates of these glaciers enlarge Fe input, thus having a greater role in supplying iron and counteracting the reductions in sea ice cover around Terra Nova Bay
ROMA: a map-making algorithm for polarised CMB data sets
We present ROMA, a parallel code to produce joint optimal temperature and
polarisation maps out of multidetector CMB observations. ROMA is a fast,
accurate and robust implementation of the iterative generalised least squares
approach to map-making. We benchmark ROMA on realistic simulated data from the
last, polarisation sensitive, flight of BOOMERanG.Comment: Accepted for publication in Astronomy & Astrophysics. Version with
higher quality figures available at http://www.fisica.uniroma2.it/~cosmo/ROM
Non-Gaussian bubbles in the sky
We point out a possible generation mechanism of non-Gaussian bubbles in the
sky due to bubble nucleation in the early universe. We consider a curvaton
scenario for inflation and assume that the curvaton field phi, whose energy
density is subdominant during inflation but which is responsible for the
curvature perturbation of the universe, is coupled to another field sigma which
undergoes false vacuum decay through quantum tunneling. For this model, we
compute the skewness of the curvaton fluctuations due to its interaction with
sigma during tunneling, that is, on the background of an instanton solution
that describes false vacuum decay. We find that the resulting skewness of the
curvaton can become large in the spacetime region inside the bubble. We then
compute the corresponding skewness in the statistical distribution of the
cosmic microwave background (CMB) temperature fluctuations. We find a
non-vanishing skewness in a bubble-shaped region in the sky. It can be large
enough to be detected in the near future, and if detected it will bring us
invaluable information about the physics in the early universe.Comment: 6 pages, 6 figure
Power Asymmetries in the Cosmic Microwave Background Temperature and Polarization patterns
We test the asymmetry of the Cosmic Microwave Background anisotropy jointly
in temperature and polarization. We study the hemispherical asymmetry,
previously found only in the temperature field, with respect to the axis
identified by Hansen et al. (2009). To this extent, we make use of the low
resolution WMAP 5 year temperature and polarization Nside=16 maps and the
optimal angular power spectrum estimator BolPol (Gruppuso et al. 2009). We
consider two simple estimators for the power asymmetry and we compare our
findings with Monte Carlo simulations which take into account the full noise
covariance matrix. We confirm an excess of power in temperature angular power
spectrum in the Southern hemisphere at a significant level, between 3 sigma and
4 sigma depending on the exact range of multipoles considered. We do not find
significant power asymmetry in the gradient (curl) component EE (BB) of
polarized angular spectra. Also cross-correlation power spectra, i.e. TE, TB,
EB, show no significant hemispherical asymmetry. We also show that the Cold
Spot found by Vielva et al. (2004) in the Southern Galactic hemisphere does not
alter the significance of the hemispherical asymmetries on multipoles which can
be probed by maps at resolution Nside=16. Although the origin of the
hemispherical asymmetry in temperature remains unclear, the study of the
polarization patter could add useful information on its explanation. We
therefore forecast by Monte Carlo the Planck capabilities in probing
polarization asymmetries.Comment: 6 pages, 7 figure
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