87 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
Testing chirality of primordial gravitational waves with Planck and future CMB data: no hope from angular power spectra
We use the 2015 Planck likelihood in combination with the Bicep2/Keck
likelihood (BKP and BK14) to constrain the chirality, , of primordial
gravitational waves in a scale-invariant scenario. In this framework, the
parameter enters theory always coupled to the tensor-to-scalar ratio,
, e.g. in combination of the form . Thus, the capability to
detect critically depends on the value of . We find that with present
data set is \textit{de facto}unconstrained. We also provide forecasts
for from future CMB experiments, including COrE+, exploring several
fiducial values of . We find that the current limit on is tight enough
to disfavor a neat detection of . For example, in the unlikely case in
which , the maximal chirality case, i.e. , could
be detected with a significance of at best. We conclude
that the two-point statistics at the basis of CMB likelihood functions is
currently unable to constrain chirality and may only provide weak limits on
in the most optimistic scenarios. Hence, it is crucial to investigate
the use of other observables, e.g. provided by higher order statistics, to
constrain these kind of parity violating theories with the CMB.Comment: 15 pages, 3 figures. Updated to match published versio
A note on the birefringence angle estimation in CMB data analysis
Parity violating physics beyond the standard model of particle physics
induces a rotation of the linear polarization of photons. This effect, also
known as cosmological birefringence (CB), can be tested with the observations
of the cosmic microwave background (CMB) anisotropies which are linearly
polarized at the level of . In particular CB produces non-null CMB
cross correlations between temperature and B mode-polarization, and between E-
and B-mode polarization. Here we study the properties of the so called
D-estimators, often used to constrain such an effect. After deriving the
framework of both frequentist and Bayesian analysis, we discuss the interplay
between birefringence and weak-lensing, which, albeit parity conserving,
modifies pre-existing TB and EB cross correlation.Comment: 12 pages. Accepted for publication in JCA
Boundaries and the Casimir effect in non-commutative space-time
We calculate modifications to the scalar Casimir force between two parallel
plates due to space-time non-commutativity. We devise a heuristic approach to
overcome the difficulties of describing boundaries in non-commutative theories
and predict that boundary corrections are of the same order as non-commutative
volume corrections. Further, both corrections have the form of more
conventional finite surface effects.Comment: 9 pages, 2 figure
Cosmic Birefringence: Cross-Spectra and Cross-Bispectra with CMB Anisotropies
Parity-violating extensions of Maxwell electromagnetism induce a rotation of
the linear polarization plane of photons during propagation. This effect, known
as cosmic birefringence, impacts on the Cosmic Microwave Background (CMB)
observations producing a mixing of and polarization modes which is
otherwise null in the standard scenario. Such an effect is naturally
parametrized by a rotation angle which can be written as the sum of an
isotropic component and an anisotropic one
. In this paper we compute angular power
spectra and bispectra involving and the CMB temperature and
polarization maps. In particular, contrarily to what happens for the
cross-spectra, we show that even in absence of primordial cross-correlations
between the anisotropic birefringence angle and the CMB maps, there exist
non-vanishing three-point correlation functions carrying signatures of
parity-breaking physics. Furthermore, we find that such angular bispectra still
survive in a regime of purely anisotropic cosmic birefringence, which
corresponds to the conservative case of having . These bispectra
represent an additional observable aimed at studying cosmic birefringence and
its parity-violating nature beyond power spectrum analyses. They provide also a
way to perform consistency checks for specific models of cosmic birefringence.
Moreover, we estimate that among all the possible birefringent bispectra,
and are the
ones which contain the largest signal-to-noise ratio. Once the cosmic
birefringence signal is taken to be at the level of current constraints, we
show that these bispectra are within reach of future CMB experiments, as
LiteBIRD.Comment: 22 pages, 5 figures; added references; typos corrected; matches
published versio
Probing Axions through Tomography of Anisotropic Cosmic Birefringence
Cosmic birefringence is the in-vacuo rotation of the linear polarization
plane experienced by photons of the Cosmic Microwave Background (CMB) radiation
when theoretically well-motivated parity-violating extensions of Maxwell
electromagnetism are considered. If the angle, parametrizing such a rotation is
dependent on the photon's direction, then this phenomenon is called Anisotropic
Cosmic Birefringence (ACB). In this paper, we perform for the first time a
tomographic treatment of the ACB, by considering photons emitted both at the
recombination and reionization epoch. This allows one to extract additional and
complementary information about the physical source of cosmic birefringence
with respect to the isotropic case. We focus here on the case of an axion-like
field , whose coupling with the electromagnetic sector induces such a
phenomenon, by using an analytical and numerical approach (which involves a
modification of the CLASS code). We find that the anisotropic component of
cosmic birefringence exhibits a peculiar behavior: an increase of the axion
mass implies an enhancement of the anisotropic amplitude, allowing to probe a
wider range of masses with respect to the purely isotropic case. Moreover, we
show that at large angular scales, the interplay between the reionization and
recombination contributions to ACB is sensitive to the axion mass, so that at
sufficiently low multipoles, for sufficiently light masses, the reionization
contribution overtakes the recombination one, making the tomographic approach
to cosmic birefringence a promising tool for investigating the properties of
this axion-like field.Comment: 24 pages, 5 figures. Added brief information about the algorithms
used for reionization and recombination in Fig
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