1,721,067 research outputs found
Constraints on parity violation from ACTpol and forecasts for forthcoming CMB experiments
No full textWe use the ACTpol published cosmic microwave background (CMB) polarization data to constrain cosmological birefringence, a tracer of parity violation beyond the standard model of particle physics. To this purpose, we employ all the polarized ACTpol spectra, including the cross-correlations between temperature anisotropy and B mode polarization (TB) and between E mode and B mode (EB), which are most sensitive to the effect. We build specific, so-called D-estimators for birefringence and assess their performances and error budgets by using realistic Monte Carlo simulations based on the experimental characteristics provided by the ACTpol collaboration. We determine the optimal multipole range for our analysis to be 250<l<3025 over which we find a null result for the uniform birefringence angle α=0.29°±0.28° (stat.) ±0.5° (syst.), the latter uncertainty being the estimate published by the ACTpol team on their global systematic error budget. We show that this result holds consistently when other multipole ranges are considered. Finally, we forecast the capability of several forthcoming ground based, balloon and space borne CMB experiments to constrain the birefringence angle, showing, e.g., that the proposed post-Planck COrE satellite mission could in principle constrain α at a level of 10 arcsec, provided that all systematics are under control. Under the same circumstances, we find the COrE constraints to be at least 2 or 3 times better than what could ideally be achieved by the other experiments considered
Cosmic Birefringence: Cross-Spectra and Cross-Bispectra with CMB Anisotropies
Full text linkParity-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; typos correcte
A new solution for the observed isotropic cosmic birefringence angle and its implications for the anisotropic counterpart through a Boltzmann approach
Full text linkCosmic Birefringence (CB) is a phenomenon in which the polarization of the Cosmic Microwave Background (CMB) radiation is rotated as it travels through space due to the coupling between photons and an axion-like field. We look for a solution able to explain the result obtained from the Planck Public Release 4 (PR4), which has provided a hint of detection of the CB angle, alpha = (0.30 +/- 0.11)degrees. degrees . In addition to the solutions, already present in the literature, which need a non-negligible evolution in time of the axion-like field during recombination, we find a new region of the parameter space that allows for a nearly constant time evolution of such a field in the same epoch. The latter reinforces the possibility to employ the commonly used relations connecting the observed CMB spectra with the unrotated ones, through trigonometric functions of the CB angle. However, if the homogeneous axion field sourcing isotropic birefringence is almost constant in time during the matter-dominated era, this does not automatically imply that the same holds also for the associated inhomogeneous perturbations. For this reason, in this paper we present a fully generalized Boltzmann treatment of this phenomenon, that is able, for the first time to our knowledge to deal with the time evolution of anisotropic cosmic birefringence (ACB). We employ this approach to provide predictions of ACB, in particular for the set of best-fit parameters found in the new solution of the isotropic case. If the latter is the correct model, we expect an ACB spectrum of the order of (10-15 - 15 = 10-32) - 32 ) deg2 2 for the auto-correlation, and (10-7 - 7 = 10-17) - 17 ) mu Kdeg deg for the cross-correlations with the CMB T and E fields, depending on the angular scale
CMB low multipole alignments in the ΛCDM and dipolar models
No full textThe dipolar model [1] has attracted much interest because it may phenomenologically explain the CMB hemispherical power asymmetry found in the WMAP and Planck data. Since such a model explicitly breaks isotropy at large angular scales it is natural to wonder whether it can also explain other CMB directional anomalies. Focusing on the low l alignments and assuming ΛCDM, we confirm that the quadrupole/octupole and the dipole/quadrupole/octupole alignments are anomalous with a significance up to 99.9% C.L., for both WMAP and Planck data. Moreover, we show for the first time that such features are anomalous also in the dipolar model, roughly at the same level as in ΛCDM. We conclude that the dipolar model does not provide a better fit to the data than the ΛCDM
A note on the birefringence angle estimation in CMB data analysis
No full textParity 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 5-10%. 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
Probing Axions through Tomography of Anisotropic Cosmic Birefringence
Full text linkCosmic 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. Matched the published version on JCA
Testing chirality of primordial gravitational waves with Planck and future CMB data: No hope from angular power spectra
No full textWe use the 2015 Planck likelihood in combination with the Bicep2/Keck likelihood (BKP and BK14) to constrain the chirality, chi, of primordial gravitational waves in a scale invariant scenario. In this framework, the parameter chi enters theory always coupled to the tensor -to -scalar ratio, r, e.g. in combination of the form chi . r. Thus, the capability to detect chi critically depends on the value of r. We find that with present data sets chi is de facto unconstrained. We also provide forecasts for chi from future CMB experiments, including COrE+, exploring several fiducial values of r. We find that the current limit on r is tight enough to disfavor a neat detection of chi. For example, in the unlikely case in which r similar to 0.1(0.05), the maximal chirality case, i.e. chi = +/- 1, could be detected with a significance of similar to 2.5(1.5)sigma 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 chi 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 kinds of parity violating theories with the CMB.We use the 2015 Planck likelihood in combination with the Bicep2/Keck likelihood (BKP and BK14) to constrain the chirality, χ, of primordial gravitational waves in a scale-invariant scenario. In this framework, the parameter χ enters theory always coupled to the tensor-to-scalar ratio, r, e.g. in combination of the form χ ċ r. Thus, the capability to detect χ critically depends on the value of r. We find that with present data sets χ is de facto unconstrained. We also provide forecasts for χ from future CMB experiments, including COrE+, exploring several fiducial values of r. We find that the current limit on r is tight enough to disfavor a neat detection of χ. For example, in the unlikely case in which r∼0.1(0.05), the maximal chirality case, i.e. χ = ±1, could be detected with a significance of ∼2.5(1.5)σ 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 χ in the m..
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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