3,276 research outputs found
Cosmic Birefringence: Cross-Spectra and Cross-Bispectra with CMB Anisotropies
No full textParity-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
Probing Axions through Tomography of Anisotropic Cosmic Birefringence
No full textCosmic 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
A new solution for the observed isotropic cosmic birefringence angle and its implications for the anisotropic counterpart through a Boltzmann approach
No full textCosmic 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
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
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 imagem de Alessandro Baricco no Brasil
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão, Programa de Pós-Graduação em Estudos da Tradução, Florianópolis, 2013.Com a intenção de delinear o modo pelo qual o escritor italiano Alessandro Baricco se inseriu no sistema literário brasileiro e os caminhos percorridos pelos seus livros traduzidos, esta dissertação dá voz às experiências tradutórias de seus tradutores. A inserção de Bariccono Brasil tem seu início em 1997, através de uma proposição da Profa. Dra. Roberta Barni à editora Iluminuras da tradução de Oceano Mare. A partir daí, outras sete obras foram publicadas no Brasil, sendo três delas traduzidas por Roberta Barni e as outras quatro por quatro tradutores diferentes. De um lado, considera-se o tradutor como figura principal namediação entre culturas, e, de outro, se analisa a realidade desta figuradentro do sistema literário, sua invisibilidade, seus limites e o exercíciode sua profissão. A pesquisa conta, ainda, com críticas e resenhas referentes ao autor italiano publicadas em jornais consagrados no Brasil, considerando estas como parte constituinte da imagem de Baricco refletida em território nacional. Abstract : Intending to delineate the way the Italian writer Alessandro Baricco has been inserted in the Brazilian literary system and the paths his translated books have followed, this thesis gives voice to the translating experiences of his translators. Baricco's insertion in Brazil began in 1997, through a personal project of Dr. Roberta Barni, with her translation of Oceano Mare. Since then, seven other of his works have been published in Brazil, three of which were translated by Roberta Barni and the other four by four different translators. On the one hand,the translator is considered as the main figure in mediation betweencultures and, on the other, this figure's reality is analyzed within theliterary system: its invisibility, its limits and its professional practice. Criticisms and reviews of this Italian author published in well established Brazilian newspapers are also considered, with the understanding that they are part of Baricco's image reflected here
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..
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
La maturità di Alessandro Fei del Barbiere, in bilico tra Maniera e Riforma
No full textThis article studies the mature career of the Florentine painter Alessandro Fei del Barbiere (1537-1592), beginning with the rediscovery of the 'Ascension' altarpiece formerly in the Albizi Chapel in the destroyed church of San Pier Maggiore, Florence. Studying this painting and others recorded in 1584 by the biographer Raffaello Borghini, such as the two altarpieces for Santa Maria delle Grazie and the Madonna dell'Umiltà in Pistoia, the author reconstructs a body of works showing how in the 1580s Fei gradually went beyond the archaic style of his apprenticeship - he had been trained by Ridolfo del Ghirlandaio and Pierfrancesco Foschi, but was also marked by the Maniera of Vasari - evolving towards naturalism in both mimesis and pictorial handling. In Florence, his development partly parallels that of Santi di Tito and his circle, but Fei was also influenced by a probable sojourn during the early part of that decade in Rome, where he could have been inspired by Girolamo Muziano and the painters working for Pope Gregory XIII. Among other proposals, the author suggests that the artist was responsible for decorating the chancel of Fiesole Cathedral (c. 1584-1589), which consisted of an altarpiece, only rarely discussed by scholars, and a cycle of frescoes hitherto attributed to Nicodemo Ferrucci
Pre-Inflationary Relics in the CMB?
No full textString Theory and Supergravity allow, in principle, to follow the transition of the inflaton from pre-inflationary fast roll to slow roll. This introduces an infrared depression in the primordial power spectrum that might have left an imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We model the effect extending CDM with a scale related to the infrared depression and explore the constraints allowed by {\sc Planck} data, employing also more conservative, wider Galactic masks in the low resolution CMB likelihood. In an extended mask with , we thus find \Delta = (0.351 \pm 0.114) \times 10^{-3} \, \mbox{Mpc}^{-1}, at confidence level, to be compared with a nearby value at with the standard mask. With about 64 --folds of inflation, these values for would translate into primordial energy scales GeV.String Theory and Supergravity allow, in principle, to follow the transition of the inflaton from pre-inflationary fast roll to slow roll. This introduces an infrared depression in the primordial power spectrum that might have left an imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We model the effect extending CDM with a scale related to the infrared depression and explore the constraints allowed by {\sc Planck} data, employing also more conservative, wider Galactic masks in the low resolution CMB likelihood. In an extended mask with , we thus find \Delta = (0.351 \pm 0.114) \times 10^{-3} \, \mbox{Mpc}^{-1}, at confidence level, to be compared with a nearby value at with the standard mask. With about 64 --folds of inflation, these values for would translate into primordial energy scales GeV.String Theory and Supergravity allow, in principle, to follow the transition of the inflaton from pre-inflationary fast roll to slow roll. This introduces an infrared depression in the primordial power spectrum that might have left an imprint in the CMB anisotropy, if it occurred at accessible wavelengths. We model the effect extending ΛCDM with a scale Δ related to the infrared depression and explore the constraints allowed by Planck 2015 data, employing also more conservative, wider Galactic masks in the low resolution CMB likelihood. In an extended mask with fsky=39% , we thus find Δ=(0.351±0.114)×10−3Mpc−1 , at 99.4% confidence level, to be compared with a nearby value at 88.5% with the standard fsky=94% mask. With about 64 e -folds of inflation, these values for Δ would translate into primordial energy scales O(1014)GeV
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