56 research outputs found
On the dipole straylight contamination in spinning space missions dedicated to CMB anisotropy
We present an analysis of the dipole straylight contamination (DSC) for
spinning space-missions designed to measure CMB anisotropies. Although this
work is mainly devoted to the {\sc Planck} project, it is relatively general
and allows to focus on the most relevant DSC implications. We first study a
simple analytical model for the DSC in which the pointing direction of the main
spillover can be assumed parallel or not to the spacecraft spin axis direction
and compute the time ordered data and map. The map is then analysed paying
particular attention to the DSC of the low multipole coefficients of the map.
Through dedicated numerical simulations we verify the analytical results and
extend the analysis to higher multipoles and to more complex (and realistic)
cases by relaxing some of the simple assumptions adopted in the analytical
approach. We find that the systematic effect averages out in an even number of
surveys, except for a contamination of the dipole itself that survives when
spin axis and spillover directions are not parallel and for a contamination of
the other multipoles in the case of complex scanning strategies. In particular,
the observed quadrupole can be affected by the DSC in an odd number of surveys
or in the presence of survey uncompleteness or over-completeness. Various
aspects relevant in CMB space projects (such as implications for calibration,
impact on polarization measurements, accuracy requirement in the far beam
knowledge for data analysis applications, scanning strategy dependence) are
discussed.Comment: 21 pages, 13 Figures, 1 Table. To appear in MNRAS. Accepted 2006 July
13. Received 2006 July 13; in original form 2006 June 7. This work has been
done in the framework of the Planck LFI activitie
DELPHIC: Practical DEL Planning via Possibilities (Extended Version)
Dynamic Epistemic Logic (DEL) provides a framework for epistemic planning
that is capable of representing non-deterministic actions, partial
observability, higher-order knowledge and both factual and epistemic change.
The high expressivity of DEL challenges existing epistemic planners, which
typically can handle only restricted fragments of the whole framework. The goal
of this work is to push the envelop of practical DEL planning, ultimately
aiming for epistemic planners to be able to deal with the full range of
features offered by DEL. Towards this goal, we question the traditional
semantics of DEL, defined in terms on Kripke models. In particular, we propose
an equivalent semantics defined using, as main building block, so-called
possibilities: non well-founded objects representing both factual properties of
the world, and what agents consider to be possible. We call the resulting
framework DELPHIC. We argue that DELPHIC indeed provides a more compact
representation of epistemic states. To substantiate this claim, we implement
both approaches in ASP and we set up an experimental evaluation to compare
DELPHIC with the traditional, Kripke-based approach. The evaluation confirms
that DELPHIC outperforms the traditional approach in space and time
A Semantic Approach to Decidability in Epistemic Planning (Extended Version)
The use of Dynamic Epistemic Logic (DEL) in multi-agent planning has led to a
widely adopted action formalism that can handle nondeterminism, partial
observability and arbitrary knowledge nesting. As such expressive power comes
at the cost of undecidability, several decidable fragments have been isolated,
mainly based on syntactic restrictions of the action formalism. In this paper,
we pursue a novel semantic approach to achieve decidability. Namely, rather
than imposing syntactical constraints, the semantic approach focuses on the
axioms of the logic for epistemic planning. Specifically, we augment the logic
of knowledge S5 and with an interaction axiom called (knowledge)
commutativity, which controls the ability of agents to unboundedly reason on
the knowledge of other agents. We then provide a threefold contribution. First,
we show that the resulting epistemic planning problem is decidable. In doing
so, we prove that our framework admits a finitary non-fixpoint characterization
of common knowledge, which is of independent interest. Second, we study
different generalizations of the commutativity axiom, with the goal of
obtaining decidability for more expressive fragments of DEL. Finally, we show
that two well-known epistemic planning systems based on action templates, when
interpreted under the setting of knowledge, conform to the commutativity axiom,
hence proving their decidability
A comparison of CMB Angular Power Spectrum Estimators at Large Scales: the TT case
In the context of cosmic microwave background (CMB) data analysis, we compare
the efficiency at large scale of two angular power spectrum algorithms,
implementing, respectively, the quadratic maximum likelihood (QML) estimator
and the pseudo spectrum (pseudo-Cl) estimator. By exploiting 1000 realistic
Monte Carlo (MC) simulations, we find that the QML approach is markedly
superior in the range l=[2-100]. At the largest angular scales, e.g. l < 10,
the variance of the QML is almost 1/3 (1/2) that of the pseudo-Cl, when we
consider the WMAP kq85 (kq85 enlarged by 8 degrees) mask, making the pseudo
spectrum estimator a very poor option. Even at multipoles l=[20-60], where
pseudo-Cl methods are traditionally used to feed the CMB likelihood algorithms,
we find an efficiency loss of about 20%, when we considered the WMAP kq85 mask,
and of about 15% for the kq85 mask enlarged by 8 degrees. This should be taken
into account when claiming accurate results based on pseudo-Cl methods. Some
examples concerning typical large scale estimators are provided.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
On the impact of large angle CMB polarization data on cosmological parameters
(abridged) We study the impact of the large-angle CMB polarization datasets
publicly released by the WMAP and Planck satellites on the estimation of
cosmological parameters of the CDM model. To complement large-angle
polarization, we consider the high-resolution CMB datasets from either WMAP or
Planck, as well as CMB lensing as traced by Planck. In the case of WMAP, we
compute the large-angle polarization likelihood starting over from
low-resolution frequency maps and their covariance matrices, and perform our
own foreground mitigation technique, which includes as a possible alternative
Planck 353 GHz data to trace polarized dust. We find that the latter choice
induces a downward shift in the optical depth , of order ~,
robust to the choice of the complementary high-l dataset. When the Planck 353
GHz is consistently used to minimize polarized dust emission, WMAP and Planck
70 GHz large-angle polarization data are in remarkable agreement: by combining
them we find , again very stable against the
particular choice for high- data. We find that the amplitude of
primordial fluctuations , notoriously degenerate with , is the
parameter second most affected by the assumptions on polarized dust removal,
but the other parameters are also affected, typically between and
. In particular, cleaning dust with \planck's 353 GHz data imposes a
downward shift in the value of the Hubble constant ,
significantly contributing to the tension reported between CMB based and direct
measurements of . On the other hand, we find that the appearance of the
so-called low anomaly, a well-known tension between the high- and
low-resolution CMB anisotropy amplitude, is not significantly affected by the
details of large-angle polarization, or by the particular high- dataset
employed.Comment: 19 pages, 4 figures, 3 table
Recent results and perspectives on cosmology and fundamental physics from microwave surveys
Recent cosmic microwave background data in temperature and polarization have
reached high precision in estimating all the parameters that describe the
current so-called standard cosmological model. Recent results about the
integrated Sachs-Wolfe effect from cosmic microwave background anisotropies,
galaxy surveys, and their cross-correlations are presented. Looking at fine
signatures in the cosmic microwave background, such as the lack of power at low
multipoles, the primordial power spectrum and the bounds on non-Gaussianities,
complemented by galaxy surveys, we discuss inflationary physics and the
generation of primordial perturbations in the early Universe. Three important
topics in particle physics, the bounds on neutrinos masses and parameters, on
thermal axion mass and on the neutron lifetime derived from cosmological data
are reviewed, with attention to the comparison with laboratory experiment
results. Recent results from cosmic polarization rotation analyses aimed at
testing the Einstein equivalence principle are presented. Finally, we discuss
the perspectives of next radio facilities for the improvement of the analysis
of future cosmic microwave background spectral distortion experiments.Comment: 27 pages, 9 figures. Review Article. International Journal of Modern
Physics D, in press. [Will appear also on the proceedings of the Fourteenth
Marcel Grossmann Meeting University of Rome "La Sapienza" - Rome, July 12-18,
2015 (http://www.icra.it/mg/mg14/), eds. Robert T. Jantzen, Kjell Rosquist,
Remo Ruffini. World Scientific, Singapore
SKA synergy with Microwave Background studies
The extremely high sensitivity and resolution of the Square Kilometre Array (SKA) will be useful for addressing a wide set of themes relevant for cosmology, in synergy with current and future cosmic microwave background (CMB) projects. Many of these themes also have a link with future optical-IR and X-ray observations. We discuss the scientific perspectives for these goals, the instrumental requirements and the observational and data analysis approaches, and identify several topics that are important for cosmology and astrophysics at different cosmic epochs
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